研究者データベース
| GREVE RALF GUNTHER(グレーベ ラルフ ギユンター) |
| 低温科学研究所 雪氷新領域部門 |
| 教授 |
Last Updated :2024/05/09
基本情報
所属
職名
学位
- Habilitation in Mechanics（2000年02月 ダルムシュタット工科大学）
- 理学博士（1995年08月 ダルムシュタット工科大学）
- 物理学修士（1991年12月 ダルムシュタット工科大学）
ホームページURL
科研費研究者番号
- 90374644
ORCID ID
J-Global ID
プロフィール
2004年から北海道大学低温科学研究所で氷河･氷床の研究をしています。ドイツのダルムシュタット工科大学で物理学を学び、1995年に理学博士を取得、以来ポリサーマル氷床の動力学、熱力学を理論、解析、数値モデルを使い研究を続けています。2003年まではダルムシュタット工科大学力学部において研究員、助手、講師を務めました。学術論文は自著、共著を合わせると100を超え、氷力学と連続体力学の２冊の教科書の著者でもあります。さらに、「Journal of Glaciology」の副編集長、オープンソースの氷床モデルSICOPOLISを維持管理しています。
研究キーワード
研究分野
担当教育組織
職歴
- 2004年01月 - 現在 北海道大学 低温科学研究所 教授
- 2000年05月 - 2003年12月 ダルムシュタット工科大学 力学部 講師
- 1997年12月 - 2003年12月 ダルムシュタット工科大学 力学部 助手
- 1995年08月 - 1997年12月 ダルムシュタット工科大学 力学部 研究員
学歴
所属学協会
研究活動情報
論文
- Hélène Seroussi, Vincent Verjans, Sophie Nowicki, Antony J. Payne, Heiko Goelzer, William H. Lipscomb, Ayako Abe-Ouchi, Cécile Agosta, Torsten Albrecht, Xylar Asay-Davis, Alice Barthel, Reinhard Calov, Richard Cullather, Christophe Dumas, Benjamin K. Galton-Fenzi, Rupert Gladstone, Nicholas R. Golledge, Jonathan M. Gregory, Ralf Greve, Tore Hattermann, Matthew J. Hoffman, Angelika Humbert, Philippe Huybrechts, Nicolas C. Jourdain, Thomas Kleiner, Eric Larour, Gunter R. Leguy, Daniel P. Lowry, Chistopher M. Little, Mathieu Morlighem, Frank Pattyn, Tyler Pelle, Stephen F. Price, Aurélien Quiquet, Ronja Reese, Nicole-Jeanne Schlegel, Andrew Shepherd, Erika Simon, Robin S. Smith, Fiammetta Straneo, Sainan Sun, Luke D. Trusel, Jonas Van Breedam, Peter Van Katwyk, Roderik S. W. van de Wal, Ricarda Winkelmann, Chen Zhao, Tong Zhang, Thomas ZwingerThe Cryosphere 17 12 5197 - 5217 2023年12月07日 [査読有り][通常論文]
The Antarctic Ice Sheet represents the largest source of uncertainty in future sea level rise projections, with a contribution to sea level by 2100 ranging from −5 to 43 cm of sea level equivalent under high carbon emission scenarios estimated by the recent Ice Sheet Model Intercomparison for CMIP6 (ISMIP6). ISMIP6 highlighted the different behaviors of the East and West Antarctic ice sheets, as well as the possible role of increased surface mass balance in offsetting the dynamic ice loss in response to changing oceanic conditions in ice shelf cavities. However, the detailed contribution of individual glaciers, as well as the partitioning of uncertainty associated with this ensemble, have not yet been investigated. Here, we analyze the ISMIP6 results for high carbon emission scenarios, focusing on key glaciers around the Antarctic Ice Sheet, and we quantify their projected dynamic mass loss, defined here as mass loss through increased ice discharge into the ocean in response to changing oceanic conditions. We highlight glaciers contributing the most to sea level rise, as well as their vulnerability to changes in oceanic conditions. We then investigate the different sources of uncertainty and their relative role in projections, for the entire continent and for key individual glaciers. We show that, in addition to Thwaites and Pine Island glaciers in West Antarctica, Totten and Moscow University glaciers in East Antarctica present comparable future dynamic mass loss and high sensitivity to ice shelf basal melt. The overall uncertainty in additional dynamic mass loss in response to changing oceanic conditions, compared to a scenario with constant oceanic conditions, is dominated by the choice of ice sheet model, accounting for 52 % of the total uncertainty of the Antarctic dynamic mass loss in 2100. Its relative role for the most dynamic glaciers varies between 14 % for MacAyeal and Whillans ice streams and 56 % for Pine Island Glacier at the end of the century. The uncertainty associated with the choice of climate model increases over time and reaches 13 % of the uncertainty by 2100 for the Antarctic Ice Sheet but varies between 4 % for Thwaites Glacier and 53 % for Whillans Ice Stream. The uncertainty associated with the ice–climate interaction, which captures different treatments of oceanic forcings such as the choice of melt parameterization, its calibration, and simulated ice shelf geometries, accounts for 22 % of the uncertainty at the ice sheet scale but reaches 36 % and 39 % for Institute Ice Stream and Thwaites Glacier, respectively, by 2100. Overall, this study helps inform future research by highlighting the sectors of the ice sheet most vulnerable to oceanic warming over the 21st century and by quantifying the main sources of uncertainty. - John C. Moore, Ralf Greve, Chao Yue, Thomas Zwinger, Fabien Gillet‐Chaulet, Liyun ZhaoJournal of Geophysical Research: Earth Surface 128 11 e2023JF007112 2023年11月27日 [査読有り][通常論文]
Sea level rise (SLR) due to surface melt and to dynamic losses from the ice sheets—that is via accelerated flow of glaciers into the sea—is something that may be potentially mitigated by cooling the ice sheet and oceans via solar geoengineering. We use two ice dynamic models driven by changes in surface mass balance (SMB) from four climate models to estimate the SLR contribution from the Greenland ice sheet under the Intergovernmental Panel on Climate Change (IPCC) Representative Concentration Pathway (RCP) 4.5, and 8.5, and Geoengineering Model Intercomparison Project G4 scenarios. The G4 scenario adds 5 Tg/yr sulfate aerosols to the equatorial lower stratosphere (equivalent of 1/4 the 1991 Mt Pinatubo SO2 eruption) to the IPCC RCP4.5 scenario, which itself approximates the greenhouse gas emission commitments agreed in Paris in 2015. Over the 2020–2090 period, mass loss under G4 is about 31%–38% that under RCP4.5, which is 36%–48% lower than under RCP8.5. Ice lost across the grounding line under both G4 and RCP4.5 is reduced in the future as the termini of many southeast Greenland outlets retreat onto bedrock above sea level. Glaciers with large low‐lying catchments in the west, north, and northeast of Greenland (e.g., Jakobshavn, 79N, Zachariae Isstrøm, and Petermann glaciers) discharge more ice from the ice‐sheet interior under RCP4.5 than under G4. Although calving losses vary much more than the SMB difference between ice dynamic models, both models point to significant ice discharge losses of between 15% and 42% across the scenarios. - Ralf Greve, Christopher Chambers, Takashi Obase, Fuyuki Saito, Wing-Le Chan, Ayako Abe-OuchiJournal of Glaciology 1 - 11 2023年07月11日 [査読有り][通常論文]
As part of the Coupled Model Intercomparison Project Phase 6 (CMIP6), the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6) was devised to assess the likely sea-level-rise contribution from the Earth's ice sheets. Here, we construct an ensemble of climate forcings for Antarctica until the year 2300 based on original ISMIP6 forcings until 2100, combined with climate indices from simulations with the MIROC4m climate model until 2300. We then use these forcings to run simulations for the Antarctic ice sheet with the SICOPOLIS model. For the unabated warming pathway RCP8.5/SSP5-8.5, the ice sheet suffers a severe mass loss, amounting to ~ 1.5 m SLE (sea-level equivalent) for the fourteen-experiment mean, and ~ 3.3 m SLE for the most sensitive experiment. Most of this loss originates from West Antarctica. For the reduced emissions pathway RCP2.6/SSP1-2.6, the loss is limited to a three-experiment mean of ~ 0.16 m SLE. The means are approximately two times larger than what was found in a previous study (Chambers and others, 2022, doi:10.1017/jog.2021.124) that assumed a sustained late-21st-century climate beyond 2100, demonstrating the importance of post-2100 climate trends on Antarctic mass changes in the 22nd and 23rd centuries. - Shreyas Sunil Gaikwad, Laurent Hascoet, Sri Hari Krishna Narayanan, Liz Curry-Logan, Ralf Greve, Patrick HeimbachJournal of Open Source Software 8 83 4679 2023年03月07日 [査読有り][通常論文]
SImulation COde for POLythermal Ice Sheets (SICOPOLIS) is an open-source, 3D dynamic/thermodynamic model that simulates the evolution of large ice sheets and ice caps. SICOPOLIS has been developed continuously and applied to problems of past, present, and future glaciation of Greenland, Antarctica, and others. It uses the finite differences discretization on a staggered Arakawa C grid and employs the shallow ice and shallow shelf approximations, making it suitable for paleoclimatic simulations. We present a new framework for generating derivative code, i.e., tangent linear, adjoint, or Hessian models, of SICOPOLIS. These derivative operators are powerful computational engines to efficiently compute comprehensive gradients or sensitivities of scalar-valued model output, including least-squares model-data misfits or important quantities of interest, to high-dimensional model inputs (such as model initial conditions, parameter fields, or boundary conditions). The new version 2 (SICOPOLIS-AD v2) framework is based on the source-to-source automatic differentiation (AD) tool Tapenade which has recently been open-sourced. The switch from a previous AD tool (OpenAD) used in SICOPOLIS-AD version 1 to Tapenade overcomes several limitations outlined here. The framework is integrated with the SICOPOLIS model's main trunk and is freely available. - Mass loss of the Antarctic ice sheet until the year 3000 under a sustained late-21st-century climateChristopher Chambers, Ralf Greve, Takashi Obase, Fuyuki Saito, Ayako Abe-OuchiJournal of Glaciology 68 269 605 - 617 2022年06月 [査読有り][通常論文]
Ice-sheet simulations of Antarctica extending to the year 3000 are analysed to investigate the long-term impacts of 21st-century warming. Climate projections are used as forcing until 2100 and afterwards no climate trend is applied. Fourteen experiments are for the 'unabated warming' pathway, and three are for the 'reduced emissions' pathway. For the unabated warming path simulations, West Antarctica suffers a much more severe ice loss than East Antarctica. In these cases, the mass loss amounts to an ensemble average of similar to 3.5 m sea-level equivalent (SLE) by the year 3000 and similar to 5.3 m for the most sensitive experiment. Four phases of mass loss occur during the collapse of the West Antarctic ice sheet. For the reduced emissions pathway, the mean mass loss is similar to 0.24 m SLE. By demonstrating that the consequences of the 21st century unabated warming path forcing are large and long term, the results present a different perspective to ISMIP6 (Ice Sheet Model Intercomparison Project for CMIP6). Extended ABUMIP (Antarctic BUttressing Model Intercomparison Project) simulations, assuming sudden and sustained iceshelf collapse, with and without bedrock rebound, corroborate a negative feedback for ice loss found in previous studies, where bedrock rebound acts to slow the rate of ice loss. - Mass loss of the Greenland ice sheet until the year 3000 under a sustained late-21st-century climateRalf Greve, Christopher ChambersJournal of Glaciology 68 269 618 - 624 2022年06月 [査読有り][通常論文]
We conduct extended versions of the ISMIP6 future climate experiments for the Greenland ice sheet until the year 3000 with the model SICOPOLIS. Beyond 2100, the climate forcing is kept fixed at late-21st-century conditions. For the unabated warming pathway RCP8.5/SSP5-8.5, the ice sheet suffers a severe mass loss, which amounts to similar to 1.8 m SLE (sea-level equivalent) for the 12-experiment mean, and similar to 3.5 m SLE (similar to 50% of the entire mass) for the most sensitive experiment. For the reduced emissions pathway RCP2.6/SSP1-2.6, the mass loss is limited to a two-experiment mean of similar to 0.28 m SLE. Climate-change mitigation during the next decades will therefore be an efficient means for limiting the contribution of the Greenland ice sheet to sea-level rise in the long term. - Isaac B. Smith, Nicole-Jeanne Schlegel, Eric Larour, Ignacio Isola, Peter B. Buhler, Nathaniel E. Putzig, Ralf GreveJournal of Geophysical Research: Planets 127 4 e2022JE007193 2022年04月 [査読有り][通常論文]
Massive, kilometer thick deposits of carbon dioxide (CO2) ice have been detected at the south polar cap of Mars by radar investigations. These deposits are divided into several units that are separated by thin water ice bounding layers. Recent studies investigated the accumulation history of CO2 ice and found that the deposits most likely formed during several episodes in the past, when Martian obliquity was much lower than now. Those studies, while able to predict total volumes of CO2 ice consistent with those observed, did not attempt to explain the anomalous three-dimensional distribution (thickness or extent) of CO2 ice or the ice's offset from the topographic high of the polar cap. In this paper we use a combination of feature analysis and numerical modeling to demonstrate that the CO2 deposits flow as glaciers and that glacial flow distributes the ice into its current position. Further, this distribution allows the ice to survive during high obliquity excursions. - Antony J. Payne, Sophie Nowicki, Ayako Abe-Ouchi, Cecile Agosta, Patrick Alexander, Torsten Albrecht, Xylar Asay-Davis, Andy Aschwanden, Alice Barthel, Thomas J. Bracegirdle, Reinhard Calov, Christopher Chambers, Youngmin Choi, Richard Cullather, Joshua Cuzzone, Christophe Dumas, Tamsin L. Edwards, Denis Felikson, Xavier Fettweis, Benjamin K. Galton-Fenzi, Heiko Goelzer, Rupert Gladstone, Nicholas R. Golledge, Jonathan M. Gregory, Ralf Greve, Tore Hattermann, Matthew J. Hoffman, Angelika Humbert, Philippe Huybrechts, Nicolas C. Jourdain, Thomas Kleiner, Peter Kuipers Munneke, Eric Larour, Sebastien Le Clec'h, Victoria Lee, Gunter Leguy, William H. Lipscomb, Christopher M. Little, Daniel P. Lowry, Mathieu Morlighem, Isabel Nias, Frank Pattyn, Tyler Pelle, Stephen F. Price, Aurelien Quiquet, Ronja Reese, Martin Rueckamp, Nicole-Jeanne Schlegel, Helene Seroussi, Andrew Shepherd, Erika Simon, Donald Slater, Robin S. Smith, Fiammetta Straneo, Sainan Sun, Lev Tarasov, Luke D. Trusel, Jonas Van Breedam, Roderik van de Wal, Michiel van den Broeke, Ricarda Winkelmann, Chen Zhao, Tong Zhang, Thomas ZwingerGeophysical Research Letters 48 16 e2020GL091741 2021年08月 [査読有り]
Projections of the sea level contribution from the Greenland and Antarctic ice sheets (GrIS and AIS) rely on atmospheric and oceanic drivers obtained from climate models. The Earth System Models participating in the Coupled Model Intercomparison Project phase 6 (CMIP6) generally project greater future warming compared with the previous Coupled Model Intercomparison Project phase 5 (CMIP5) effort. Here we use four CMIP6 models and a selection of CMIP5 models to force multiple ice sheet models as part of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6). We find that the projected sea level contribution at 2100 from the ice sheet model ensemble under the CMIP6 scenarios falls within the CMIP5 range for the Antarctic ice sheet but is significantly increased for Greenland. Warmer atmosphere in CMIP6 models results in higher Greenland mass loss due to surface melt. For Antarctica, CMIP6 forcing is similar to CMIP5 and mass gain from increased snowfall counteracts increased loss due to ocean warming. - Matthias Scheiter, Marius Schaefer, Eduardo Flandez, Deniz Bozkurt, Ralf GreveThe Cryosphere 15 8 3637 - 3654 2021年08月 [査読有り]
Glaciers and ice caps are thinning and retreating along the entire Andes ridge, and drivers of this mass loss vary between the different climate zones. The southern part of the Andes (Wet Andes) has the highest abundance of glaciers in number and size, and a proper understanding of ice dynamics is important to assess their evolution. In this contribution, we apply the ice-sheet model SICOPOLIS (SImulation COde for POLythermal Ice Sheets) to the Mocho-Choshuenco ice cap in the Chilean Lake District (40 degrees S, 72 degrees W; Wet Andes) to reproduce its current state and to project its evolution until the end of the 21st century under different global warming scenarios. First, we create a model spin-up using observed surface mass balance data on the south-eastern catchment, extrapolating them to the whole ice cap using an aspect-dependent parameterization. This spin-up is able to reproduce the most important present-day glacier features. Based on the spin-up, we then run the model 80 years into the future, forced by projected surface temperature anomalies from different global climate models under different radiative pathway scenarios to obtain estimates of the ice cap's state by the end of the 21st century. The mean projected ice volume losses are 56 +/- 16% (RCP2.6), 81 +/- 6% (RCP4.5), and 97 +/- 2% (RCP8.5) with respect to the ice volume estimated by radio-echo sounding data from 2013. We estimate the uncertainty of our projections based on the spread of the results when forcing with different global climate models and on the uncertainty associated with the variation of the equilibrium line altitude with temperature change. Considering our results, we project a considerable deglaciation of the Chilean Lake District by the end of the 21st century. - Tamsin L. Edwards, Sophie Nowicki, Ben Marzeion, Regine Hock, Heiko Goelzer, Helene Seroussi, Nicolas C. Jourdain, Donald A. Slater, Fiona E. Turner, Christopher J. Smith, Christine M. McKenna, Erika Simon, Ayako Abe-Ouchi, Jonathan M. Gregory, Eric Larour, William H. Lipscomb, Antony J. Payne, Andrew Shepherd, Cecile Agosta, Patrick Alexander, Torsten Albrecht, Brian Anderson, Xylar Asay-Davis, Andy Aschwanden, Alice Barthel, Andrew Bliss, Reinhard Calov, Christopher Chambers, Nicolas Champollion, Youngmin Choi, Richard Cullather, Joshua Cuzzone, Christophe Dumas, Denis Felikson, Xavier Fettweis, Koji Fujita, Benjamin K. Galton-Fenzi, Rupert Gladstone, Nicholas R. Golledge, Ralf Greve, Tore Hattermann, Matthew J. Hoffman, Angelika Humbert, Matthias Huss, Philippe Huybrechts, Walter Immerzeel, Thomas Kleiner, Philip Kraaijenbrink, Sebastien Le Clec'h, Victoria Lee, Gunter R. Leguy, Christopher M. Little, Daniel P. Lowry, Jan-Hendrik Malles, Daniel F. Martin, Fabien Maussion, Mathieu Morlighem, James F. O'Neill, Isabel Nias, Frank Pattyn, Tyler Pelle, Stephen F. Price, Aure'lien Quiquet, Valentina Radic, Ronja Reese, David R. Rounce, Martin Ruckamp, Akiko Sakai, Courtney Shafer, Nicole-Jeanne Schlegel, Sarah Shannon, Robin S. Smith, Fiammetta Straneo, Sainan Sun, Lev Tarasov, Luke D. Trusel, Jonas Van Breedam, Roderik van de Wal, Michiel van den Broeke, Ricarda Winkelmann, Harry Zekollari, Chen Zhao, Tong Zhang, Thomas ZwingerNature 593 7857 74 - 82 2021年05月 [査読有り][通常論文]
Efficient statistical emulation of melting land ice under various climate scenarios to 2100 indicates a contribution from melting land ice to sea level increase of at least 13 centimetres sea level equivalent.The land ice contribution to global mean sea level rise has not yet been predicted(1) using ice sheet and glacier models for the latest set of socio-economic scenarios, nor using coordinated exploration of uncertainties arising from the various computer models involved. Two recent international projects generated a large suite of projections using multiple models(2-8), but primarily used previous-generation scenarios(9) and climate models(10), and could not fully explore known uncertainties. Here we estimate probability distributions for these projections under the new scenarios(11,12) using statistical emulation of the ice sheet and glacier models. We find that limiting global warming to 1.5 degrees Celsius would halve the land ice contribution to twenty-first-century sea level rise, relative to current emissions pledges. The median decreases from 25 to 13 centimetres sea level equivalent (SLE) by 2100, with glaciers responsible for half the sea level contribution. The projected Antarctic contribution does not show a clear response to the emissions scenario, owing to uncertainties in the competing processes of increasing ice loss and snowfall accumulation in a warming climate. However, under risk-averse (pessimistic) assumptions, Antarctic ice loss could be five times higher, increasing the median land ice contribution to 42 centimetres SLE under current policies and pledges, with the 95th percentile projection exceeding half a metre even under 1.5 degrees Celsius warming. This would severely limit the possibility of mitigating future coastal flooding. Given this large range (between 13 centimetres SLE using the main projections under 1.5 degrees Celsius warming and 42 centimetres SLE using risk-averse projections under current pledges), adaptation planning for twenty-first-century sea level rise must account for a factor-of-three uncertainty in the land ice contribution until climate policies and the Antarctic response are further constrained. - Kumiko Goto-Azuma, Tomoyuki Homma, Tomotaka Saruya, Fumio Nakazawa, Yuki Komuro, Naoko Nagatsuka, Motohiro Hirabayashi, Yutaka Kondo, Makoto Koike, Teruo Aoki, Ralf Greve, Jun'ichi OkunoPolar Science 27 100557 2021年03月 [査読有り][招待有り]
We review major scientific results from Subtheme (1) "Variability of the Greenland Ice Sheet and climate" under Research Theme 2 "Variations in the ice sheet, glaciers, and the environment in the Greenland region" of the Arctic Challenge for Sustainability (ArCS) project. We participated in the international East Greenland Ice Core Project (EGRIP) led by Denmark, conducted snow pit observations near the coring site and reconstructed the surface mass balance over the past 10 years. Analyses of an ice core from Northwest Greenland revealed temporal variability in black carbon concentration over the past 350 years and in mineral dust over the past 100 years. To understand the mechanisms of ice-sheet flow, which is necessary for accurate predictions of sea level rise, we conducted laboratory experiments using artificial ice and derived an improved flow law for ice containing impurities. Ice sheet modeling was improved by including effects of impurities and ice stream dynamics. As part of the Ice Sheet Model Intercomparison Project for the Coupled Model Intercomparison Project Phase 6 (ISMIP6), we simulated ice sheet mass loss and contribution to sea level rise over the 21st century and beyond. Furthermore, we developed a Glacial Isostatic Adjustment model to better constrain ice sheet models. - Shin Sugiyama, Naoya Kanna, Daiki Sakakibara, Takuto Ando, Izumi Asaji, Ken Kondo, Yefan Wang, Yoshiki Fujishi, Shungo Fukumoto, Evgeniy Podolskiy, Yasushi Fukamachi, Minori Takahashi, Sumito Matoba, Yoshinori Iizuka, Ralf Greve, Masato Furuya, Kazutaka Tateyama, Tatsuya Watanabe, Shintaro Yamasaki, Atsushi Yamaguchi, Bungo Nishizawa, Kohei Matsuno, Daiki Nomura, Yuta Sakuragi, Yoshimasa Matsumura, Yoshihiko Ohashi, Teruo Aoki, Masashi Niwano, Naotaka Hayashi, Masahiro Minowa, Guillaume Jouvet, Eef van Dongen, Andreas Bauder, Martin Funk, Anders Anker Bjork, Toku OshimaPolar Science 27 100632 2021年03月 [査読有り][招待有り]
Environments along the coast of Greenland are rapidly changing under the influence of a warming climate in the Arctic. To better understand the changes in the coastal environments, we performed researches in the Qaanaaq region in northwestern Greenland as a part of the ArCS (Arctic Challenge for Sustainability) Project. Mass loss of ice caps and marine-terminating outlet glaciers were quantified by field and satellite observations. Measurements and sampling in fjords revealed the important role of glacial meltwater discharge in marine ecosystems. Flooding of a glacial stream in Qaanaaq and landslides in a nearby settlement were investigated to identify the drivers of the incidents. Our study observed rapid changes in the coastal environments, and their critical impact on the society in Qaanaaq. We organized workshops with the residents to absorb local and indigenous knowledge, as well as to share the results and data obtained in the project. Continuous effort towards obtaining long-term observations requiring involvement of local communities is crucial to contribute to a sustainable future in Greenland. - Sainan Sun, Frank Pattyn, Erika G. Simon, Torsten Albrecht, Stephen Cornford, Reinhard Calov, Christophe Dumas, Fabien Gillet-Chaulet, Heiko Goelzer, Nicholas R. Golledge, Ralf Greve, Matthew J. Hoffman, Angelika Humbert, Elise Kazmierczak, Thomas Kleiner, Gunter R. Leguy, William H. Lipscomb, Daniel Martin, Mathieu Morlighem, Sophie Nowicki, David Pollard, Stephen Price, Aurelien Quiquet, Helene Seroussi, Tanja Schlemm, Johannes Sutter, Roderik S. W. van de Wal, Ricarda Winkelmann, Tong ZhangJournal of Glaciology 66 260 891 - 904 2020年12月 [査読有り]
Antarctica's ice shelves modulate the grounded ice flow, and weakening of ice shelves due to climate forcing will decrease their 'buttressing' effect, causing a response in the grounded ice. While the processes governing ice-shelf weakening are complex, uncertainties in the response of the grounded ice sheet are also difficult to assess. The Antarctic BUttressing Model Intercomparison Project (ABUMIP) compares ice-sheet model responses to decrease in buttressing by investigating the 'end-member' scenario of total and sustained loss of ice shelves. Although unrealistic, this scenario enables gauging the sensitivity of an ensemble of 15 ice-sheet models to a total loss of buttressing, hence exhibiting the full potential of marine ice-sheet instability. All models predict that this scenario leads to multi-metre (1-12 m) sea-level rise over 500 years from present day. West Antarctic ice sheet collapse alone leads to a 1.91-5.08 m sea-level rise due to the marine ice-sheet instability. Mass loss rates are a strong function of the sliding/friction law, with plastic laws cause a further destabilization of the Aurora and Wilkes Subglacial Basins, East Antarctica. Improvements to marine ice-sheet models have greatly reduced variability between modelled ice-sheet responses to extreme ice-shelf loss, e.g. compared to the SeaRISE assessments. - Christopher Chambers, Ralf Greve, Bas Altena, Pierre-Marie LefeuvreThe Cryosphere 14 11 3747 - 3759 2020年11月 [査読有り]
Greenland basal topographic data show a segmented valley extending from Petermann Fjord into the centre of Greenland; however, the locations of radar scan lines, used to create the bedrock topography data, indicate that valley segmentation is due to data interpolation. Therefore, as a thought experiment, simulations where the valley is opened are used to investigate its effects on basal water movement and distribution. The simulations indicate that the opening of this valley can result in an uninterrupted water pathway from the interior to Petermann Fjord. Along its length, the path of the valley progresses gradually down an ice surface slope, causing a lowering of ice overburden pressure that could enable water flow along its path. The fact that the valley base appears to be relatively flat and follows a path near the interior ice divide that roughly intersects the east and west basal hydrological basins is presented as evidence that its present day form may have developed in conjunction with an overlying ice sheet. Experiments where basal melting is increased solely within the deep interior near the known large area of basal melting result in an increase in the flux of water northwards along the entire valley. The results are consistent with a long subglacial river; however, considerable uncertainty remains over aspects such as whether adequate water is available at the bed, whether water escapes from the valley or is refrozen, and over what form a hydrological conduit could take along the valley base. - The future sea-level contribution of the Greenland ice sheet: a multi-model ensemble study of ISMIP6Heiko Goelzer, Sophie Nowicki, Anthony Payne, Eric Larour, Helene Seroussi, William H. Lipscomb, Jonathan Gregory, Ayako Abe-Ouchi, Andrew Shepherd, Erika Simon, Cecile Agosta, Patrick Alexander, Andy Aschwanden, Alice Barthel, Reinhard Calov, Christopher Chambers, Youngmin Choi, Joshua Cuzzone, Christophe Dumas, Tamsin Edwards, Denis Felikson, Xavier Fettweis, Nicholas R. Golledge, Ralf Greve, Angelika Humbert, Philippe Huybrechts, Sebastien Le Clec'h, Victoria Lee, Gunter Leguy, Chris Little, Daniel P. Lowry, Mathieu Morlighem, Isabel Nias, Aurelien Quiquet, Martin Rueckamp, Nicole-Jeanne Schlegel, Donald A. Slater, Robin S. Smith, Fiamma Straneo, Lev Tarasov, Roderik van de Wal, Michiel van den BroekeThe Cryosphere 14 9 3071 - 3096 2020年09月 [査読有り][通常論文]
The Greenland ice sheet is one of the largest contributors to global mean sea-level rise today and is expected to continue to lose mass as the Arctic continues to warm. The two predominant mass loss mechanisms are increased surface meltwater run-off and mass loss associated with the retreat of marine-terminating outlet glaciers. In this paper we use a large ensemble of Greenland ice sheet models forced by output from a representative subset of the Coupled Model Intercomparison Project (CMIP5) global climate models to project ice sheet changes and sea-level rise contributions over the 21st century. The simulations are part of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6). We estimate the sea-level contribution together with uncertainties due to future climate forcing, ice sheet model formulations and ocean forcing for the two greenhouse gas concentration scenarios RCP8.5 and RCP2.6. The results indicate that the Greenland ice sheet will continue to lose mass in both scenarios until 2100, with contributions of 90 ± 50 and 32 ± 17mm to sea-level rise for RCP8.5 and RCP2.6, respectively. The largest mass loss is expected from the south-west of Greenland, which is governed by surface mass balance changes, continuing what is already observed today. Because the contributions are calculated against an unforced control experiment, these numbers do not include any committed mass loss, i.e. mass loss that would occur over the coming century if the climate forcing remained constant. Under RCP8.5 forcing, ice sheet model uncertainty explains an ensemble spread of 40 mm, while climate model uncertainty and ocean forcing uncertainty account for a spread of 36 and 19 mm, respectively. Apart from those formally derived uncertainty ranges, the largest gap in our knowledge is about the physical understanding and implementation of the calving process, i.e. the interaction of the ice sheet with the ocean. - ISMIP6 Antarctica: a multi-model ensemble of the Antarctic ice sheet evolution over the 21st centuryHelene Seroussi, Sophie Nowicki, Antony J. Payne, Heiko Goelzer, William H. Lipscomb, Ayako Abe-Ouchi, Cecile Agosta, Torsten Albrecht, Xylar Asay-Davis, Alice Barthel, Reinhard Calov, Richard Cullather, Christophe Dumas, Benjamin K. Galton-Fenzi, Rupert Gladstone, Nicholas R. Golledge, Jonathan M. Gregory, Ralf Greve, Tore Hattermann, Matthew J. Hoffman, Angelika Humbert, Philippe Huybrechts, Nicolas C. Jourdain, Thomas Kleiner, Eric Larour, Gunter R. Leguy, Daniel P. Lowry, Chistopher M. Little, Mathieu Morlighem, Frank Pattyn, Tyler Pelle, Stephen F. Price, Aurelien Quiquet, Ronja Reese, Nicole-Jeanne Schlegel, Andrew Shepherd, Erika Simon, Robin S. Smith, Fiammetta Straneo, Sainan Sun, Luke D. Trusel, Jonas Van Breedam, Roderik S. W. van de Wal, Ricarda Winkelmann, Chen Zhao, Tong Zhang, Thomas ZwingerThe Cryosphere 14 9 3033 - 3070 2020年09月 [査読有り][通常論文]
Ice flow models of the Antarctic ice sheet are commonly used to simulate its future evolution in response to different climate scenarios and assess the mass loss that would contribute to future sea level rise. However, there is currently no consensus on estimates of the future mass balance of the ice sheet, primarily because of differences in the representation of physical processes, forcings employed and initial states of ice sheet models. This study presents results from ice flow model simulations from 13 international groups focusing on the evolution of the Antarctic ice sheet during the period 2015-2100 as part of the Ice Sheet Model Intercomparison for CMIP6 (ISMIP6). They are forced with outputs from a subset of models from the Coupled Model Intercomparison Project Phase 5 (CMIP5), representative of the spread in climate model results. Simulations of the Antarctic ice sheet contribution to sea level rise in response to increased warming during this period varies between −7.8 and 30.0 cm of sea level equivalent (SLE) under Representative Concentration Pathway (RCP) 8.5 scenario forcing. These numbers are relative to a control experiment with constant climate conditions and should therefore be added to the mass loss contribution under climate conditions similar to present-day conditions over the same period. The simulated evolution of the West Antarctic ice sheet varies widely among models, with an overall mass loss, up to 18.0 cm SLE, in response to changes in oceanic conditions. East Antarctica mass change varies between −6.1 and 8.3 cm SLE in the simulations, with a significant increase in surface mass balance outweighing the increased ice discharge under most RCP 8.5 scenario forcings. The inclusion of ice shelf collapse, here assumed to be caused by large amounts of liquid water ponding at the surface of ice shelves, yields an additional simulated mass loss of 28mm compared to simulations without ice shelf collapse. The largest sources of uncertainty come from the climate forcing, the ocean-induced melt rates, the calibration of these melt rates based on oceanic conditions taken outside of ice shelf cavities and the ice sheet dynamic response to these oceanic changes. Results under RCP 2.6 scenario based on two CMIP5 climate models show an additional mass loss of 0 and 3 cm of SLE on average compared to simulations done under present-day conditions for the two CMIP5 forcings used and display limited mass gain in East Antarctica. - Alexander Robinson, Jorge Alvarez-Solas, Marisa Montoya, Heiko Goelzer, Ralf Greve, Catherine RitzGeoscientific Model Development 13 6 2805 - 2823 2020年06月 [査読有り][通常論文]
We describe the physics and features of the ice-sheet model Yelmo, an open-source project intended for collaborative development. Yelmo is a thermomechanical model, solving for the coupled velocity and temperature solutions of an ice sheet simultaneously. The ice dynamics are currently treated via a "hybrid" approach combining the shallow-ice and shallow-shelf/shelfy-stream approximations, which makes Yelmo an apt choice for studying a wide variety of problems. Yelmo's main innovations lie in its flexible and user-friendly infrastructure, which promotes portability and facilitates long-term development. In particular, all physics subroutines have been designed to be self-contained, so that they can be easily ported from Yelmo to other models, or easily replaced by improved or alternate methods in the future. Furthermore, hard-coded model choices are eschewed, replaced instead with convenient parameter options that allow the model to be adapted easily to different contexts. We show results for different ice-sheet benchmark tests, and we illustrate Yelmo's performance for the Antarctic ice sheet. - Liz C. Logan, Sri Hari Krishna Narayanan, Ralf Greve, Patrick HeimbachGeoscientific Model Development 13 4 1845 - 1864 2020年04月 [査読有り][通常論文]
We present a new capability of the ice sheet model SICOPOLIS that enables flexible adjoint code generation via source transformation using the open-source algorithmic differentiation (AD) tool OpenAD. The adjoint code enables efficient calculation of the sensitivities of a scalar-valued objective function or quantity of interest (QoI) to a range of important, often spatially varying and uncertain model input variables, including initial and boundary conditions, as well as model parameters. Compared to earlier work on the adjoint code generation of SICOPOLIS, our work makes several important advances: (i) it is embedded within the up-to-date trunk of the SICOPOLIS repository - accounting for 1.5 decades of code development and improvements - and is readily available to the wider community; (ii) the AD tool used, OpenAD, is an open-source tool; (iii) the adjoint code developed is applicable to both Greenland and Antarctica, including grounded ice as well as floating ice shelves, with an extended choice of thermodynamical representations. A number of code refactorization steps were required. They are discussed in detail in an Appendix as they hold lessons for the application of AD to legacy codes at large. As an example application, we examine the sensitivity of the total Antarctic Ice Sheet volume to changes in initial ice thickness, austral summer precipitation, and basal and surface temperatures across the ice sheet. Simulations of Antarctica with floating ice shelves show that over 100 years of simulation the sensitivity of total ice sheet volume to the initial ice thickness and precipitation is almost uniformly positive, while the sensitivities to surface and basal temperature are almost uniformly negative. Sensitivity to austral summer precipitation is largest on floating ice shelves from Queen Maud to Queen Mary Land. The largest sensitivity to initial ice thickness is at outlet glaciers around Antarctica. Comparison between total ice sheet volume sensitivities to surface and basal temperature shows that surface temperature sensitivities are higher broadly across the floating ice shelves, while basal temperature sensitivities are highest at the grounding lines of floating ice shelves and outlet glaciers. A uniformly perturbed region of East Antarctica reveals that, among the four control variables tested here, total ice sheet volume is the most sensitive to variations in austral summer precipitation as formulated in SICOPOLIS. Comparison between adjoint- and finite-difference-derived sensitivities shows good agreement, lending confidence that the AD tool is producing correct adjoint code. The new modeling infrastructure is freely available at http://www.sicopolis.net (last access: 2 April 2020) under the development trunk. - Anders Levermann, Ricarda Winkelmann, Torsten Albrecht, Heiko Goelzer, Nicholas R. Golledge, Ralf Greve, Philippe Huybrechts, Jim Jordan, Gunter Leguy, Daniel Martin, Mathieu Morlighem, Frank Pattyn, David Pollard, Aurelien Quiquet, Christian Rodehacke, Helene Seroussi, Johannes Sutter, Tong Zhang, Jonas Van Breedam, Reinhard Calov, Robert DeConto, Christophe Dumas, Julius Garbe, G. Hilmar Gudmundsson, Matthew J. Hoffman, Angelika Humbert, Thomas Kleiner, William H. Lipscomb, Malte Meinshausen, Esmond Ng, Sophie M. J. Nowicki, Mauro Perego, Stephen F. Price, Fuyuki Saito, Nicole-Jeanne Schlegel, Sainan Sun, Roderik S. W. van de WalEarth System Dynamics 11 1 35 - 76 2020年02月 [査読有り][通常論文]
The sea level contribution of the Antarctic ice sheet constitutes a large uncertainty in future sea level projections. Here we apply a linear response theory approach to 16 state-of-the-art ice sheet models to estimate the Antarctic ice sheet contribution from basal ice shelf melting within the 21st century. The purpose of this computation is to estimate the uncertainty of Antarctica's future contribution to global sea level rise that arises from large uncertainty in the oceanic forcing and the associated ice shelf melting. Ice shelf melting is considered to be a major if not the largest perturbation of the ice sheet's flow into the ocean. However, by computing only the sea level contribution in response to ice shelf melting, our study is neglecting a number of processes such as surface-mass-balance-related contributions. In assuming linear response theory, we are able to capture complex temporal responses of the ice sheets, but we neglect any self-dampening or self-amplifying processes. This is particularly relevant in situations in which an instability is dominating the ice loss. The results obtained here are thus relevant, in particular wherever the ice loss is dominated by the forcing as opposed to an internal instability, for example in strong ocean warming scenarios. In order to allow for comparison the methodology was chosen to be exactly the same as in an earlier study (Levermann et al., 2014) but with 16 instead of 5 ice sheet models. We include uncertainty in the atmospheric warming response to carbon emissions (full range of CMIP5 climate model sensitivities), uncertainty in the oceanic transport to the Southern Ocean (obtained from the time-delayed and scaled oceanic subsurface warming in CMIP5 models in relation to the global mean surface warming), and the observed range of responses of basal ice shelf melting to oceanic warming outside the ice shelf cavity. This uncertainty in basal ice shelf melting is then convoluted with the linear response functions of each of the 16 ice sheet models to obtain the ice flow response to the individual global warming path. The model median for the observational period from 1992 to 2017 of the ice loss due to basal ice shelf melting is 10.2 mm, with a likely range between 5.2 and 21.3 mm For the same period the Antarctic ice sheet lost mass equivalent to 7.4 mm of global sea level rise, with a standard deviation of 3.7 mm (Shepherd et al., 2018) including all processes, especially surface-mass-balance changes. For the unabated warming path, Representative Concentration Pathway 8.5 (RCP8.5), we obtain a median contribution of the Antarctic ice sheet to global mean sea level rise from basal ice shelf melting within the 21st century of 17 cm, with a likely range (66th percentile around the mean) between 9 and 36 cm and a very likely range (90th percentile around the mean) between 6 and 58 cm. For the RCP2.6 warming path, which will keep the global mean temperature below 2 degrees C of global warming and is thus consistent with the Paris Climate Agreement, the procedure yields a median of 13 cm of global mean sea level contribution. The likely range for the RCP2.6 scenario is between 7 and 24 cm, and the very likely range is between 4 and 37 cm. The structural uncertainties in the method do not allow for an interpretation of any higher uncertainty percentiles. We provide projections for the five Antarctic regions and for each model and each scenario separately. The rate of sea level contribution is highest under the RCP8.5 scenario.The maximum within the 21st century of the median value is 4 cm per decade, with a likely range between 2 and 9 cm per decade and a very likely range between 1 and 14 cm per decade. - Soroush Rezvanbehbahani, Leigh A. Stearns, C. J. Van der Veen, Gordon K. A. Oswald, Ralf GreveJournal of Glaciology 65 254 1023 - 1034 2019年12月 [査読有り][通常論文]
The spatial distribution of basal water critically impacts the evolution of ice sheets. Current estimates of basal water distribution beneath the Greenland Ice Sheet (GrIS) contain large uncertainties due to poorly constrained boundary conditions, primarily from geothermal heat flux (GHF). The existing GHF models often contradict each other and implementing them in numerical ice-sheet models cannot reproduce the measured temperatures at ice core locations. Here we utilize two datasets of radar-detected basal water in Greenland to constrain the GHF at regions with a thawed bed. Using the three-dimensional ice-sheet model SICOPOLIS, we iteratively adjust the GHF to find the minimum GHF required to reach the bed to the pressure melting point, GHF_pmp, at locations of radar-detected basal water. We identify parts of the central-east, south and northwest Greenland with significantly high GHF_pmp. Conversely, we find that the majority of low-elevation regions of west Greenland and parts of northeast have very low GHF_pmp. We compare the estimated constraints with the available GHF models for Greenland and show that GHF models often do not honor the estimated constraints. Our results highlight the need for community effort to reconcile the discrepancies between radar data, GHF models, and ice core information. - Martin Rückamp, Ralf Greve, Angelika HumbertPolar Science 21 14 - 25 2019年09月 [査読有り][通常論文]
Projections of the contribution of the Greenland ice sheet to sea level rise comprise uncertainties that arise from the imposed climate forcing and from the underlying mathematical and numerical description used by ice flow models. Here, we present a comparative modelling study with the models SICOPOLIS, using the shallow ice approximation (SIA) on a structured grid, and ISSM, using a higher-order (HO) approximation of the Stokes equation on an unstructured grid. Starting from a paleoclimatic spin-up produced by SICOPOLIS, the models are forced with two different, simplified warming scenarios based on RCP2.6 projections from climate models, which are in line with the limit of global warming negotiated for the Paris Agreement. ISSM/HO produces lower flow speeds at the glacier termini, but more acceleration in narrow outlet glaciers compared to SICOPOLIS/SIA. This leads to a larger elevation reduction for ISSM/HO, and thus a positive feedback on the surface mass balance (with that of ISSM/HO becoming similar to 50 Gt/a more negative). Across the two models and scenarios, the projected mass loss by 2300 is similar to 62-88 mm sea level equivalent. - Helene Seroussi, Sophie Nowicki, Erika Simon, Ayako Abe-Ouchi, Torsten Albrecht, Julien Brondex, Stephen Cornford, Christophe Dumas, Fabien Gillet-Chaulet, Heiko Goelzer, Nicholas R. Golledge, Jonathan M. Gregory, Ralf Greve, Matthew J. Hoffman, Angelika Humbert, Philippe Huybrechts, Thomas Kleiner, Eric Larour, Gunter Leguy, William H. Lipscomb, Daniel Lowry, Matthias Mengel, Mathieu Morlighem, Frank Pattyn, Anthony J. Payne, David Pollard, Stephen F. Price, Aurelien Quiquet, Thomas J. Reerink, Ronja Reese, Christian B. Rodehacke, Nicole-Jeanne Schlegel, Andrew Shepherd, Sainan Sun, Johannes Sutter, Jonas Van Breedam, Roderik S. W. van de Wal, Ricarda Winkelmann, Tong ZhangThe Cryosphere 13 5 1441 - 1471 2019年05月 [査読有り][通常論文]
Ice sheet numerical modeling is an important tool to estimate the dynamic contribution of the Antarctic ice sheet to sea level rise over the coming centuries. The influence of initial conditions on ice sheet model simulations, however, is still unclear. To better understand this influence, an initial state intercomparison exercise (initMIP) has been developed to compare, evaluate, and improve initialization procedures and estimate their impact on century-scale simulations. initMlP is the first set of experiments of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6), which is the primary Coupled Model Intercomparison Project Phase 6 (CMIP6) activity focusing on the Greenland and Antarctic ice sheets. Following initMlP-Greenland, initMlP-Antarctica has been designed to explore uncertainties associated with model initialization and spin-up and to evaluate the impact of changes in external forcings. Starting from the state of the Antarctic ice sheet at the end of the initialization procedure, three forward experiments are each run for 100 years: a control run, a run with a surface mass balance anomaly, and a run with a basal melting anomaly beneath floating ice. This study presents the results of initMlP-Antarctica from 25 simulations performed by 16 international modeling groups. The submitted results use different initial conditions and initialization methods, as well as ice flow model parameters and reference external forcings. We find a good agreement among model responses to the surface mass balance anomaly but large variations in responses to the basal melting anomaly. These variations can be attributed to differences in the extent of ice shelves and their upstream tributaries, the numerical treatment of grounding line, and the initial ocean conditions applied, suggesting that ongoing efforts to better represent ice shelves in continental-scale models should continue. - Hakime Seddik, Ralf Greve, Daiki Sakakibara, Shun Tsutaki, Masahiro Minowa, Shin SugiyamaJournal of Glaciology 65 250 225 - 238 2019年04月 [査読有り][通常論文]
We use the full-Stokes model Elmer/Ice to investigate the present dynamics of Bowdoin Glacier, a marine-terminating outlet glacier in northwestern Greenland. Short-term speed variations of the glacier were observed, correlating with air temperature and precipitation, and with the semi-diurnal ocean tides. We use a control inverse method to determine the distribution of basal friction. This reveals that most of the glacier area is characterized by near-plug-flow conditions, while some sticky spots are also identified. We then conduct experiments to test the sensitivity of the glacier flow to basal lubrication and tidal forcing at the calving front. Reduction of the basal drag by 10-40% produces speed-ups that agree approximately with the observed range of speed-ups that result from warm weather and precipitation events. In agreement with the observations, tidal forcing and surface speed near the calving front are found to be in anti-phase (high tide corresponds to low speed, and vice versa). However, the amplitude of the semi-diurnal variability is underpredicted by a factor similar to 3, which is likely related to either inaccuracies in the surface and bedrock topographies or mechanical weakening due to crevassing. - Ralf GrevePolar Data Journal 3 22 - 36 2019年02月 [査読有り][通常論文]
We present a distribution of the geothermal heat flux (GHF) for Greenland, which is an update of two earlier versions by Greve (2005, Ann. Glaciol. 42) and Greve and Herzfeld (2013, Ann. Glaciol. 54). The GHF distribution is constructed in two steps. First, the global representation by Pollack et al. (1993, Rev. Geophys. 31) is scaled for the area of Greenland. Second, by means of a paleoclimatic simulation carried out with the ice sheet model SICOPOLIS, the GHF values for five deep ice core locations are modified such that observed and simulated basal temperatures match closely. The resulting GHF distribution generally features low values in the south and the north-west, whereas elevated values prevail in central North Greenland and towards the north-east. The data are provided as NetCDF files on two different grids (EPSG:3413 grid, Bamber grid) that have frequently been used in modelling studies of the Greenland ice sheet, and for the three different resolutions of 5 km, 10 km and 20 km. - Reinhard Calov, Sebastian Beyer, Ralf Greve, Johanna Beckmann, Matteo Willeit, Thomas Kleiner, Martin Rückamp, Angelika Humbert, Andrey GanopolskiThe Cryosphere 12 10 3097 - 3121 2018年10月 [査読有り][通常論文]
We introduce the coupled model of the Greenland glacial system IGLOO 1.0, including the polythermal ice sheet model SICOPOLIS (version 3.3) with hybrid dynamics, the model of basal hydrology HYDRO and a parameterization of submarine melt for marine-terminated outlet glaciers. The aim of this glacial system model is to gain a better understanding of the processes important for the future contribution of the Greenland ice sheet to sea level rise under future climate change scenarios. The ice sheet is initialized via a relaxation towards observed surface elevation, imposing the palaeo-surface temperature over the last glacial cycle. As a present-day reference, we use the 1961-1990 standard climatology derived from simulations of the regional atmosphere model MAR with ERA reanalysis boundary conditions. For the palaeo-part of the spin-up, we add the temperature anomaly derived from the GRIP ice core to the years 1961-1990 average surface temperature field. For our projections, we apply surface temperature and surface mass balance anomalies derived from RCP 4.5 and RCP 8.5 scenarios created by MAR with boundary conditions from simulations with three CMIP5 models. The hybrid ice sheet model is fully coupled with the model of basal hydrology. With this model and the MAR scenarios, we perform simulations to estimate the contribution of the Greenland ice sheet to future sea level rise until the end of the 21st and 23rd centuries. Further on, the impact of elevation-surface mass balance feedback, introduced via the MAR data, on future sea level rise is inspected. In our projections, we found the Greenland ice sheet to contribute between 1.9 and 13.0 cm to global sea level rise until the year 2100 and between 3.5 and 76.4 cm until the year 2300, including our simulated additional sea level rise due to elevation-surface mass balance feedback. Translated into additional sea level rise, the strength of this feedback in the year 2100 varies from 0.4 to 1.7 cm, and in the year 2300 it ranges from 1.7 to 21.8 cm. Additionally, taking the Helheim and Store glaciers as examples, we investigate the role of ocean warming and surface runoff change for the melting of outlet glaciers. It shows that ocean temperature and subglacial discharge are about equally important for the melting of the examined outlet glaciers. - Heiko Goelzer, Sophie Nowicki, Tamsin Edwards, Matthew Beckley, Ayako Abe-Ouchi, Andy Aschwanden, Reinhard Calov, Olivier Gagliardini, Fabien Gillet-Chaulet, Nicholas R. Golledge, Jonathan Gregory, Ralf Greve, Angelika Humbert, Philippe Huybrechts, Joseph H. Kennedy, Eric Larour, William H. Lipscomb, Sebastien Le Clec'h, Victoria Lee, Mathieu Morlighem, Frank Pattyn, Antony J. Payne, Christian Rodehacke, Martin Rückamp, Fuyuki Saito, Nicole Schlegel, Helene Seroussi, Andrew Shepherd, Sainan Sun, Roderik van de Wal, Florian A. ZiemenThe Cryosphere 12 4 1433 - 1460 2018年04月 [査読有り][通常論文]
Earlier large-scale Greenland ice sheet sea-level projections (e.g. those run during the ice2sea and SeaRISE initiatives) have shown that ice sheet initial conditions have a large effect on the projections and give rise to important uncertainties. The goal of this initMIP-Greenland intercomparison exercise is to compare, evaluate, and improve the initialisation techniques used in the ice sheet modelling community and to estimate the associated uncertainties in modelled mass changes. initMIP-Greenland is the first in a series of ice sheet model intercomparison activities within ISMIP6 (the Ice Sheet Model Intercomparison Project for CMIP6), which is the primary activity within the Coupled Model Intercomparison Project Phase 6 (CMIP6) focusing on the ice sheets. Two experiments for the large-scale Greenland ice sheet have been designed to allow intercomparison between participating models of (1) the initial present-day state of the ice sheet and (2) the response in two idealised forward experiments. The forward experiments serve to evaluate the initialisation in terms of model drift (forward run without additional forcing) and in response to a large perturbation (prescribed surface mass balance anomaly); they should not be interpreted as sea-level projections. We present and discuss results that highlight the diversity of data sets, boundary conditions, and initialisation techniques used in the community to generate initial states of the Greenland ice sheet. We find good agreement across the ensemble for the dynamic response to surface mass balance changes in areas where the simulated ice sheets overlap but differences arising from the initial size of the ice sheet. The model drift in the control experiment is reduced for models that participated in earlier intercomparison exercises. - 齋藤 冬樹, グレーベ ラルフ低温科学 76 179 - 186 低温科学研究所 2018年03月 [査読無し][招待有り]
本稿では，氷床モデルについての概観を述べた上で，種々の氷床モデルの中でも特に氷床形状を決 めるためのモデルを概観する．氷床モデルで氷床をどのように抽象化して表現しているかを解説し， 具体例として氷床や棚氷の性質を理解する上での，二つの基本的な氷床モデルを紹介する． - Hakime Seddik, Ralf Greve, Thomas Zwinger, Shin SugiyamaThe Cryosphere 11 5 2213 - 2229 2017年09月 [査読有り][通常論文]
A hierarchy of approximations of the force balance for the flow of grounded ice exists, ranging from the most sophisticated full Stokes (FS) formulation to the most simplified shallow ice approximation (SIA). Both are implemented in the ice flow model Elmer/Ice, and we compare them by applying the model to the East Antarctic Shirase drainage basin. First, we apply the control inverse method to infer the distribution of basal friction with FS. We then compare FS and SIA by simulating the flow of the drainage basin under present-day conditions and for three scenarios 100 years into the future defined by the SeaRISE (Sea-level Response to Ice Sheet Evolution) project. FS reproduces the observed flow pattern of the drainage basin well, in particular the zone of fast flow near the grounding line, while SIA generally overpredicts the surface velocities. As for the transient scenarios, the ice volume change (relative to the constant-climate control run) of the surface climate experiment is nearly the same for FS and SIA, while for the basal sliding experiment (halved basal friction), the ice volume change is similar to 30% larger for SIA than for FS. This confirms findings of earlier studies that, in order to model ice sheet areas containing ice streams and outlet glaciers with high resolution and precision, careful consideration must be given to the choice of a suitable force balance. - Ralf Greve, Reinhard Calov, Ute C. Herzfeld低温科学 75 117 - 129 低温科学研究所 2017年03月 [査読無し][招待有り]
Numerical modelling has become established as an important tool for understanding ice sheet dynamics in general, and in particular for assessing the contribution of the Greenland and Antarctic ice sheets to future sea level change under global warming conditions. In this paper, we review related work carried out with the ice sheet model SICOPOLIS (SImulation COde for POLythermal Ice Sheets). As part of a group of eight models, it was applied to a set of standardised experiments for the Greenland ice sheet defined by the SeaRISE (Sea-level Response to Ice Sheet Evolution) initiative. A main finding of SeaRISE was that, if climate change continues unabatedly, the ice sheet may experience a significant decay over the next centuries. However, the spread of results across different models was very large, mainly because of differences in the applied initialisation methods and surface mass balance schemes. Therefore, the new initiative ISMIP6 (Ice Sheet Modeling Intercomparison Project for CMIP6) was launched. An early sub-project is InitMIP-Greenland, within which we showed that two different initialisations computed with SICOPOLIS lead indeed to large differences in the simulated response to schematic future climate scenarios. Further work within ISMIP6 will thus focus on improved initialisation techniques. Based on this, refined future climate simulations for the Greenland ice sheet, driven by forcings derived from AOGCM (atmosphere-ocean general circulation model) simulations, will be carried out. The goal of ISMIP6 is to provide significantly improved estimates of ice sheet contribution to sea level rise in the coming years. - Kenji Kawamura, Ayako Abe-Ouchi, Hideaki Motoyama, Yutaka Ageta, Shuji Aoki, Nobuhiko Azuma, Yoshiyuki Fujii, Koji Fujita, Shuji Fujita, Kotaro Fukui, Teruo Furukawa, Atsushi Furusaki, Kumiko Goto-Azuma, Ralf Greve, Motohiro Hirabayashi, Takeo Hondoh, Akira Hori, Shinichiro Horikawa, Kazuho Horiuchi, Makoto Igarashi, Yoshinori Iizuka, Takao Kameda, Hiroshi Kanda, Mika Kohno, Takayuki Kuramoto, Yuki Matsushi, Morihiro Miyahara, Takayuki Miyake, Atsushi Miyamoto, Yasuo Nagashima, Yoshiki Nakayama, Takakiyo Nakazawa, Fumio Nakazawa, Fumihiko Nishio, Ichio Obinata, Rumi Ohgaito, Akira Oka, Jun'ichi Okuno, Junichi Okuyama, Ikumi Oyabu, Frederic Parrenin, Frank Pattyn, Fuyuki Saito, Takashi Saito, Takeshi Saito, Toshimitsu Sakurai, Kimikazu Sasa, Hakime Seddik, Yasuyuki Shibata, Kunio Shinbori, Keisuke Suzuki, Toshitaka Suzuki, Akiyoshi Takahashi, Kunio Takahashi, Shuhei Takahashi, Morimasa Takata, Yoichi Tanaka, Ryu Uemura, Genta Watanabe, Okitsugu Watanabe, Tetsuhide Yamasaki, Kotaro Yokoyama, Masakazu Yoshimori, Takayasu YoshimotoScience Advances 3 2 e1600446 2017年02月 [査読有り][通常論文]
Climatic variabilities on millennial and longer time scales with a bipolar seesaw pattern have been documented in paleoclimatic records, but their frequencies, relationships with mean climatic state, and mechanisms remain unclear. Understanding the processes and sensitivities that underlie these changes will underpin better understanding of the climate system and projections of its future change. We investigate the long-term characteristics of climatic variability using a new ice-core record from Dome Fuji, East Antarctica, combined with an existing long record from the Dome C ice core. Antarctic warming events over the past 720,000 years are most frequent when the Antarctic temperature is slightly below average on orbital time scales, equivalent to an intermediate climate during glacial periods, whereas interglacial and fully glaciated climates are unfavourable for a millennial-scale bipolar seesaw. Numerical experiments using a fully coupled atmosphere-ocean general circulation model with freshwater hosing in the northern North Atlantic showed that climate becomes most unstable in intermediate glacial conditions associated with large changes in sea ice and the Atlantic Meridional Overturning Circulation. Model sensitivity experiments suggest that the prerequisite for the most frequent climate instability with bipolar seesaw pattern during the late Pleistocene era is associated with reduced atmospheric CO2 concentration via global cooling and sea ice formation in the North Atlantic, in addition to extended Northern Hemisphere ice sheets. - Rupert Michael Gladstone, Roland Charles Warner, Benjamin Keith Galton-Fenzi, Olivier Gagliardini, Thomas Zwinger, Ralf GreveThe Cryosphere 11 1 319 - 329 2017年01月 [査読有り][通常論文]
Computer models are necessary for understanding and predicting marine ice sheet behaviour. However, there is uncertainty over implementation of physical processes at the ice base, both for grounded and floating glacial ice. Here we implement several sliding relations in a marine ice sheet flow-line model accounting for all stress components and demonstrate that model resolution requirements are strongly dependent on both the choice of basal sliding relation and the spatial distribution of ice shelf basal melting.Sliding relations that reduce the magnitude of the step change in basal drag from grounded ice to floating ice (where basal drag is set to zero) show reduced dependence on resolution compared to a commonly used relation, in which basal drag is purely a power law function of basal ice velocity. Sliding relations in which basal drag goes smoothly to zero as the grounding line is approached from inland (due to a physically motivated incorporation of effective pressure at the bed) provide further reduction in resolution dependence. A similar issue is found with the imposition of basal melt under the floating part of the ice shelf: melt parameterisations that reduce the abruptness of change in basal melting from grounded ice (where basal melt is set to zero) to floating ice provide improved convergence with resolution compared to parameterisations in which high melt occurs adjacent to the grounding line. Thus physical processes, such as sub-glacial outflow (which could cause high melt near the grounding line), impact on capability to simulate marine ice sheets. If there exists an abrupt change across the grounding line in either basal drag or basal melting, then high resolution will be required to solve the problem. However, the plausible combination of a physical dependency of basal drag on effective pressure, and the possibility of low ice shelf basal melt rates next to the grounding line, may mean that some marine ice sheet systems can be reliably simulated at a coarser resolution than currently thought necessary. - Jorge Bernales, Irina Rogozhina, Ralf Greve, Maik ThomasThe Cryosphere 11 1 247 - 265 2017年01月 [査読有り][通常論文]
The shallow ice approximation (SIA) is commonly used in ice-sheet models to simplify the force balance equations within the ice. However, the SIA cannot adequately reproduce the dynamics of the fast flowing ice streams usually found at the margins of ice sheets. To overcome this limitation, recent studies have introduced heuristic hybrid combinations of the SIA and the shelfy stream approximation. Here, we implement four different hybrid schemes into a model of the Antarctic Ice Sheet in order to compare their performance under present-day conditions. For each scheme, the model is calibrated using an iterative technique to infer the spatial variability in basal sliding parameters. Model results are validated against topographic and velocity data. Our analysis shows that the iterative technique compensates for the differences between the schemes, producing similar ice-sheet configurations through quantitatively different results of the sliding coefficient calibration. Despite this we observe a robust agreement in the reconstructed patterns of basal sliding parameters. We exchange the calibrated sliding parameter distributions between the schemes to demonstrate that the results of the model calibration cannot be straightforwardly transferred to models based on different approximations of ice dynamics. However, easily adaptable calibration techniques for the potential distribution of basal sliding coefficients can be implemented into ice models to overcome such incompatibility, as shown in this study. - Miwa Yokokawa, Norihiro Izumi, Kensuke Naito, Gary Parker, Tomohito Yamada, Ralf GreveJournal of Geophysical Research: Earth Surface 121 5 1023 - 1048 2016年05月 [査読有り][通常論文]
Boundary waves often form at the interface between ice and fluid flowing adjacent to it, such as ripples under river ice covers, and steps on the bed of supraglacial meltwater channels. They may also be formed by wind, such as the megadunes on the Antarctic ice sheet. Spiral troughs on the polar ice caps of Mars have been interpreted to be cyclic steps formed by katabatic wind blowing over ice. Cyclic steps are relatives of upstream-migrating antidunes. Cyclic step formation on ice is not only a mechanical but also a thermodynamic process. There have been very few studies on the formation of either cyclic steps or upstream-migrating antidunes on ice. In this study, we performed flume experiments to reproduce cyclic steps on ice by flowing water, and found that trains of steps form when the Froude number is larger than unity. The features of those steps allow them to be identified as ice-bed analogs of cyclic steps in alluvial and bedrock rivers. We performed a linear stability analysis and obtained a physical explanation of the formation of upstream-migrating antidunes, i.e., precursors of cyclic steps. We compared the results of experiments with the predictions of the analysis and found the observed steps fall in the range where the analysis predicts interfacial instability. We also found that short antidune-like undulations formed as a precursor to the appearance of well-defined steps. This fact suggests that such antidune-like undulations correspond to the instability predicted by the analysis and are precursors of cyclic steps. - Ralf Greve, Heinz BlatterPolar Science 10 1 11 - 23 2016年03月 [査読有り][通常論文]
In order to model the thermal structure of polythermal ice sheets accurately, energy-conserving schemes and correct tracking of the cold-temperate transition surface (CTS) are necessary. We compare four different thermodynamics solvers in the ice sheet model SICOPOLIS. Two exist already, namely a two-layer polythermal scheme (POLY) and a single-phase cold-ice scheme (COLD), while the other two are newly-implemented, one-layer enthalpy schemes, namely a conventional scheme (ENTC) and a melting-CTS scheme (ENTM). The comparison uses scenarios of the EISMINT Phase 2 Simplified Geometry Experiments (Payne et al., 2000, J. Glaciol. 46, 227-238). The POLY scheme is used as a reference against which the performance of the other schemes is tested. Both the COLD scheme and the ENTC scheme fail to produce a continuous temperature gradient across the CTS, which is explicitly enforced by the ENTM scheme. ENTM is more precise than ENTC for determining the position of the CTS, while the performance of both schemes is good for the temperature/water-content profiles in the entire ice column. Therefore, the one-layer enthalpy schemes ENTC and ENTM are viable, easier implementable alternatives to the POLY scheme with its need to handle two different numerical domains for cold and temperate ice. - Kazuya Kusahara, Tatsuru Sato, Akira Oka, Takashi Obase, Ralf Greve, Ayako Abe-Ouchi, Hiroyasu HasumiAnnals of Glaciology 56 69 425 - 435 2015年10月 [査読有り][通常論文]
We estimate the sea-ice extent and basal melt of Antarctic ice shelves at the Last Glacial Maximum (LGM) using a coupled ice-shelf-sea-ice-ocean model. The shape of Antarctic ice shelves, ocean conditions and atmospheric surface conditions at the LGM are different from those in the present day; these are derived from an ice-shelf-ice-sheet model, a sea-ice-ocean model and a climate model for glacial simulations, respectively. The winter sea ice in the LGM is shown to extend up to similar to 7 degrees of latitude further equatorward than in the present day. For the LGM summer, the model shows extensive sea-ice cover in the Atlantic sector and little sea ice in the other sectors. These modelled sea-ice features are consistent with those reconstructed from sea-floor sedimentary records. Total basal melt of Antarctic ice shelves in the LGM was similar to 2147 Gt/a, which is much larger than the present-day value. More warm waters originating from Circumpolar Deep Water could be easily transported into ice-shelf cavities during the LGM because the full glacial grounding line extended to shelf break regions and ice shelves overhung continental slopes. This increased transport of warm water masses underneath an ice shelf and into their basal cavities led to the high basal melt of ice shelves in the LGM. - Thomas Goelles, Carl E. Bøggild, Ralf GreveThe Cryosphere 9 5 1845 - 1856 2015年09月 [査読有り][通常論文]
Albedo is the dominant factor governing surface melt variability in the ablation area of ice sheets and glaciers. Aerosols such as mineral dust and black carbon (soot) accumulate on the ice surface and cause a darker surface and therefore a lower albedo. The darkening effect on the ice surface is currently not included in sea level projections, and the effect is unknown. We present a model framework which includes ice dynamics, aerosol transport, aerosol accumulation and the darkening effect on ice albedo and its consequences for surface melt. The model is applied to a simplified geometry resembling the conditions of the Greenland ice sheet, and it is forced by several temperature scenarios to quantify the darkening effect of aerosols on future mass loss. The effect of aerosols depends non-linearly on the temperature rise due to the feedback between aerosol accumulation and surface melt. According to our conceptual model, accounting for black carbon and dust in future projections of ice sheet changes until the year 3000 could induce an additional volume loss of 7%. Since we have ignored some feedback processes, the impact might be even larger. - Heinz Blatter, Ralf GrevePolar Science 9 2 196 - 207 2015年06月 [査読有り][通常論文]
The enthalpy method for the thermodynamics of polythermal glaciers and ice sheets is tested and verified by a one-dimensional problem (parallel-sided slab). The enthalpy method alone does not include explicitly the transition conditions at the cold-temperate transition surface (CTS) that separates the upper cold from the lower temperate layer. However, these conditions are important for correctly determining the position of the CTS. For the numerical solution of the polythermal slab problem, we consider a two-layer front-tracking scheme as well as three different one-layer schemes (conventional one-layer scheme, one-layer melting CTS scheme, one-layer freezing CTS scheme). Computed steady-state temperature and water-content profiles are verified with exact solutions, and transient solutions computed by the one-layer schemes are compared with those of the two-layer scheme, considered to be a reliable reference. While the conventional one-layer scheme (that does not include the transition conditions at the CTS) can produce correct solutions for melting conditions at the CTS, it is more reliable to enforce the transition conditions explicitly. For freezing conditions, it is imperative to enforce them because the conventional one-layer scheme cannot handle the associated discontinuities. The suggested numerical schemes are suitable for implementation in three-dimensional glacier and ice-sheet models. - Miren Vizcaino, Uwe Mikolajewicz, Florian Ziemen, Christian B. Rodehacke, Ralf Greve, Michiel R. van den BroekeGeophysical Research Letters 42 10 3927 - 3935 2015年05月 [査読有り][通常論文]
Recent observations indicate a high sensitivity of the Greenland Ice Sheet (GrIS) to climate change. We examine the coupling between the GrIS surface mass balance, elevation, and dynamical flow with one of the few coupled GrIS and atmosphere-ocean general circulation models. Bidirectional coupling from the early Holocene reveals a growing present-day GrIS in the absence of anthropogenic forcing. We identify atmospheric sources of biases in the simulated present-day GrIS and assess the GrIS sensitivity to future greenhouse gas forcing through three Representative Concentration Pathways and their extensions and to climate variability. The elevation-surface mass balance feedback contributes to future GrIS mass loss with 8-11% (by 2100), depending on the forcing scenario, and 24-31% (by 2300). Climate variability causes a 2.5 times spread in the magnitude of the simulated present-day GrIS mass trends in a three-member ensemble. Our results represent a first step toward more advanced higher resolution coupled modeling of GrIS and climate evolution. - A. Levermann, R. Winkelmann, S. Nowicki, J. L. Fastook, K. Frieler, R. Greve, H. H. Hellmer, M. A. Martin, M. Meinshausen, M. Mengel, A. J. Payne, D. Pollard, T. Sato, R. Timmermann, W. L. Wang, R. A. BindschadlerEarth System Dynamics 5 2 271 - 293 2014年08月 [査読有り][通常論文]
The largest uncertainty in projections of future sea-level change results from the potentially changing dynamical ice discharge from Antarctica. Basal ice-shelf melting induced by a warming ocean has been identified as a major cause for additional ice flow across the grounding line. Here we attempt to estimate the uncertainty range of future ice discharge from Antarctica by combining uncertainty in the climatic forcing, the oceanic response and the ice-sheet model response. The uncertainty in the global mean temperature increase is obtained from historically constrained emulations with the MAGICC-6.0 (Model for the Assessment of Greenhouse gas Induced Climate Change) model. The oceanic forcing is derived from scaling of the subsurface with the atmospheric warming from 19 comprehensive climate models of the Coupled Model Intercomparison Project (CMIP-5) and two ocean models from the EU-project Ice2Sea. The dynamic ice-sheet response is derived from linear response functions for basal ice-shelf melting for four different Antarctic drainage regions using experiments from the Sea-level Response to Ice Sheet Evolution (SeaRISE) intercomparison project with five different Antarctic ice-sheet models. The resulting uncertainty range for the historic Antarctic contribution to global sea-level rise from 1992 to 2011 agrees with the observed contribution for this period if we use the three ice-sheet models with an explicit representation of ice-shelf dynamics and account for the time-delayed warming of the oceanic subsurface compared to the surface air temperature. The median of the additional ice loss for the 21st century is computed to 0.07 m (66% range: 0.02-0.14 m; 90% range: 0.0-0.23 m) of global sea-level equivalent for the low-emission RCP-2.6 (Representative Concentration Pathway) scenario and 0.09 m (66% range: 0.04-0.21 m; 90% range: 0.01-0.37 m) for the strongest RCP-8.5. Assuming no time delay between the atmospheric warming and the oceanic subsurface, these values increase to 0.09 m (66% range: 0.04-0.17 m; 90% range: 0.02-0.25 m) for RCP-2.6 and 0.15 m (66% range: 0.07-0.28 m; 90% range: 0.04-0.43 m) for RCP-8.5. All probability distributions are highly skewed towards high values. The applied ice-sheet models are coarse resolution with limitations in the representation of grounding-line motion. Within the constraints of the applied methods, the uncertainty induced from different ice-sheet models is smaller than that induced by the external forcing to the ice sheets. - Ralf Greve, Thomas Zwinger, Yongmei GongJournal of Glaciology 60 220 397 - 398 2014年04月 [査読有り][通常論文]
- Tatsuru Sato, Takayuki Shiraiwa, Ralf Greve, Hakime Seddik, Erik Edelmann, Thomas ZwingerClimate of the Past 10 1 393 - 404 2014年02月 [査読有り][通常論文]
An ice core was retrieved in June 1998 from the Gorshkov crater glacier at the top of the Ushkovsky volcano, in central Kamchatka. This ice core is one of only two recovered from Kamchatka so far, thus filling a gap in the regional instrumental climate network. Hydrogen isotope (δD) analyses and past accumulation reconstructions were conducted for the top 140.7 m of the core, spanning 1736-1997. Two accumulation reconstruction methods were developed and applied with the Salamatin and the Elmer/Ice firn-ice dynamics models, revealing a slightly increasing or nearly stable trend, respectively. Wavelet analysis shows that the ice core records have significant decadal and multi-decadal variabilities at different times. Around 1880 the multi-decadal variability of δD became lost and its average value increased by 6%. The multi-decadal variability of reconstructed accumulation rates changed at around 1850. Reconstructed accumulation variations agree with ages of moraines in Kamchatka. Ice core signals were significantly correlated with North Pacific sea surface temperature (SST) and surface temperature (2 m temperature). δD correlates with the North Pacific Gyre Oscillation (NPGO) index after the climate regime shift in 1976/1977, but not before that. Therefore, our findings imply that the ice core record contains various information on the local, regional and large-scale climate variability in the North Pacific region. Understanding all detailed mechanisms behind the time-dependent connections between these climate patterns is challenging and requires further efforts towards multi-proxy analysis and climate modelling. - O. Gagliardini, T. Zwinger, F. Gillet-Chaulet, G. Durand, L. Favier, B. de Fleurian, R. Greve, M. Malinen, C. Martin, P. Råback, J. Ruokolainen, M. Sacchettini, M. Schäfer, H. Seddik, J. ThiesGeoscientific Model Development 6 4 1299 - 1318 2013年08月 [査読有り][通常論文]
The Fourth IPCC Assessment Report concluded that ice sheet flow models, in their current state, were unable to provide accurate forecast for the increase of polar ice sheet discharge and the associated contribution to sea level rise. Since then, the glaciological community has undertaken a huge effort to develop and improve a new generation of ice flow models, and as a result a significant number of new ice sheet models have emerged. Among them is the parallel finite-element model Elmer/Ice, based on the open-source multi-physics code Elmer. It was one of the first full-Stokes models used to make projections for the evolution of the whole Greenland ice sheet for the coming two centuries. Originally developed to solve local ice flow problems of high mechanical and physical complexity, Elmer/Ice has today reached the maturity to solve larger-scale problems, earning the status of an ice sheet model. Here, we summarise almost 10 yr of development performed by different groups. Elmer/Ice solves the full-Stokes equations, for isotropic but also anisotropic ice rheology, resolves the grounding line dynamics as a contact problem, and contains various basal friction laws. Derived fields, like the age of the ice, the strain rate or stress, can also be computed. Elmer/Ice includes two recently proposed inverse methods to infer badly known parameters. Elmer is a highly parallelised code thanks to recent developments and the implementation of a block preconditioned solver for the Stokes system. In this paper, all these components are presented in detail, as well as the numerical performance of the Stokes solver and developments planned for the future. - Ralf Greve, Ute C. HerzfeldAnnals of Glaciology 54 63 209 - 220 2013年07月 [査読有り][通常論文]
The dynamic/thermodynamic shallow-ice model SICOPOLIS is applied to the Greenland ice sheet. Paleoclimatic spin-ups from 125 ka BP until today, as well as future-climate experiments 500 years into the future, are carried out with three different grid spacings, namely 20,10 and 5 km. The scenarios are a subset of those specified by the SeaRISE (Sea-level Response to Ice Sheet Evolution) community effort. The bed topography includes improved troughs for Jakobshavn Isbrae, Helheim, Kangerdlugssuaq and Petermann glaciers, processed by an algorithm that preserves shape, orientation and continuity of the troughs on the 5 km scale. Comparison of simulated and observed present-day surface velocities shows that these ice streams and outlet glaciers are resolved with different accuracies, ranging from poor (20 km grid) to reasonably good (5 km grid). In the future-climate experiments, the simulated absolute ice volumes depend significantly on the resolution, while the sensitivities (ice volumes relative to the constant-climate control run) vary only by a few centimeters of sea-level equivalent. - Sophie Nowicki, Robert A. Bindschadler, Ayako Abe-Ouchi, Andy Aschwanden, Ed Bueler, Hyeungu Choi, Jim Fastook, Glen Granzow, Ralf Greve, Gail Gutowski, Ute Herzfeld, Charles Jackson, Jesse Johnson, Constantine Khroulev, Eric Larour, Anders Levermann, William H. Lipscomb, Maria A. Martin, Mathieu Morlighem, Byron R. Parizek, David Pollard, Stephen F. Price, Diandong Ren, Eric Rignot, Fuyuki Saito, Tatsuru Sato, Hakime Seddik, Helene Seroussi, Kunio Takahashi, Ryan Walker, Wei Li WangJournal of Geophysical Research: Earth Surface 118 2 1002 - 1024 2013年06月 [査読有り][通常論文]
Atmospheric, oceanic, and subglacial forcing scenarios from the Sea-level Response to Ice Sheet Evolution (SeaRISE) project are applied to six three-dimensional thermomechanical ice-sheet models to assess Antarctic ice sheet sensitivity over a 500 year timescale and to inform future modeling and field studies. Results indicate (i) growth with warming, except within low-latitude basins (where inland thickening is outpaced by marginal thinning); (ii) mass loss with enhanced sliding (with basins dominated by high driving stresses affected more than basins with low-surface-slope streaming ice); and (iii) mass loss with enhanced ice shelf melting (with changes in West Antarctica dominating the signal due to its marine setting and extensive ice shelves; cf. minimal impact in the Terre Adelie, George V, Oates, and Victoria Land region of East Antarctica). Ice loss due to dynamic changes associated with enhanced sliding and/or sub-shelf melting exceeds the gain due to increased precipitation. Furthermore, differences in results between and within basins as well as the controlling impact of sub-shelf melting on ice dynamics highlight the need for improved understanding of basal conditions, grounding-zone processes, ocean-ice interactions, and the numerical representation of all three. - Sophie Nowicki, Robert A. Bindschadler, Ayako Abe-Ouchi, Andy Aschwanden, Ed Bueler, Hyeungu Choi, Jim Fastook, Glen Granzow, Ralf Greve, Gail Gutowski, Ute Herzfeld, Charles Jackson, Jesse Johnson, Constantine Khroulev, Eric Larour, Anders Levermann, William H. Lipscomb, Maria A. Martin, Mathieu Morlighem, Byron R. Parizek, David Pollard, Stephen F. Price, Diandong Ren, Eric Rignot, Fuyuki Saito, Tatsuru Sato, Hakime Seddik, Helene Seroussi, Kunio Takahashi, Ryan Walker, Wei Li WangJournal of Geophysical Research: Earth Surface 118 2 1025 - 1044 2013年06月 [査読有り][通常論文]
The Sea-level Response to Ice Sheet Evolution (SeaRISE) effort explores the sensitivity of the current generation of ice sheet models to external forcing to gain insight into the potential future contribution to sea level from the Greenland and Antarctic ice sheets. All participating models simulated the ice sheet response to three types of external forcings: a change in oceanic condition, a warmer atmospheric environment, and enhanced basal lubrication. Here an analysis of the spatial response of the Greenland ice sheet is presented, and the impact of model physics and spin-up on the projections is explored. Although the modeled responses are not always homogeneous, consistent spatial trends emerge from the ensemble analysis, indicating distinct vulnerabilities of the Greenland ice sheet. There are clear response patterns associated with each forcing, and a similar mass loss at the full ice sheet scale will result in different mass losses at the regional scale, as well as distinct thickness changes over the ice sheet. All forcings lead to an increased mass loss for the coming centuries, with increased basal lubrication and warmer ocean conditions affecting mainly outlet glaciers, while the impacts of atmospheric forcings affect the whole ice sheet. - Robert A. Bindschadler, Sophie Nowicki, Ayako Abe-Ouchi, Andy Aschwanden, Hyeungu Choi, Jim Fastook, Glen Granzow, Ralf Greve, Gail Gutowski, Ute Herzfeld, Charles Jackson, Jesse Johnson, Constantine Khroulev, Anders Levermann, William H. Lipscomb, Maria A. Martin, Mathieu Morlighem, Byron R. Parizek, David Pollard, Stephen F. Price, Diandong Ren, Fuyuki Saito, Tatsuru Sato, Hakime Seddik, Helene Seroussi, Kunio Takahashi, Ryan Walker, Wei Li WangJournal of Glaciology 59 214 195 - 224 2013年04月 [査読有り][通常論文]
Ten ice-sheet models are used to study sensitivity of the Greenland and Antarctic ice sheets to prescribed changes of surface mass balance, sub-ice-shelf melting and basal sliding. Results exhibit a large range in projected contributions to sea-level change. In most cases, the ice volume above flotation lost is linearly dependent on the strength of the forcing. Combinations of forcings can be closely approximated by linearly summing the contributions from single forcing experiments, suggesting that nonlinear feedbacks are modest. Our models indicate that Greenland is more sensitive than Antarctica to likely atmospheric changes in temperature and precipitation, while Antarctica is more sensitive to increased ice-shelf basal melting. An experiment approximating the Intergovernmental Panel on Climate Change's RCP8.5 scenario produces additional first-century contributions to sea level of 22.3 and 8.1 cm from Greenland and Antarctica, respectively, with a range among models of 62 and 14 cm, respectively. By 200 years, projections increase to 53.2 and 26.7 cm, respectively, with ranges of 79 and 43 cm. Linear interpolation of the sensitivity results closely approximates these projections, revealing the relative contributions of the individual forcings on the combined volume change and suggesting that total ice-sheet response to complicated forcings over 200 years can be linearized. - F. Gillet-Chaulet, O. Gagliardini, H. Seddik, M. Nodet, G. Durand, C. Ritz, T. Zwinger, R. Greve, D. G. VaughanThe Cryosphere 6 6 1561 - 1576 2012年12月 [査読有り][通常論文]
Over the last two decades, the Greenland ice sheet (GrIS) has been losing mass at an increasing rate, enhancing its contribution to sea-level rise (SLR). The recent increases in ice loss appear to be due to changes in both the surface mass balance of the ice sheet and ice discharge (ice flux to the ocean). Rapid ice flow directly affects the discharge, but also alters ice-sheet geometry and so affects climate and surface mass balance. Present-day ice-sheet models only represent rapid ice flow in an approximate fashion and, as a consequence, have never explicitly addressed the role of ice discharge on the total GrIS mass balance, especially at the scale of individual outlet glaciers. Here, we present a new-generation prognostic ice-sheet model which reproduces the current patterns of rapid ice flow. This requires three essential developments: the complete solution of the full system of equations governing ice deformation; a variable resolution unstructured mesh to resolve outlet glaciers and the use of inverse methods to better constrain poorly known parameters using observations. The modelled ice discharge is in good agreement with observations on the continental scale and for individual outlets. From this initial state, we investigate possible bounds for the next century ice-sheet mass loss. We run sensitivity experiments of the GrIS dynamical response to perturbations in climate and basal lubrication, assuming a fixed position of the marine termini. We find that increasing ablation tends to reduce outflow and thus decreases the ice-sheet imbalance. In our experiments, the GrIS initial mass (im)balance is preserved throughout the whole century in the absence of reinforced forcing, allowing us to estimate a lower bound of 75 mm for the GrIS contribution to SLR by 2100. In one experiment, we show that the current increase in the rate of ice loss can be reproduced and maintained throughout the whole century. However, this requires a very unlikely perturbation of basal lubrication. From this result we are able to estimate an upper bound of 140 mm from dynamics only for the GrIS contribution to SLR by 2100. - On the influence of Greenland outlet glacier bed topography on results from dynamic ice-sheet modelsUte C. Herzfeld, James Fastook, Ralf Greve, Brian McDonald, Bruce F. Wallin, Philip A. ChenAnnals of Glaciology 53 60 281 - 293 2012年11月 [査読有り][通常論文]
Prediction of future changes in dynamics of the Earth's ice sheets, mass loss and resultant contribution to sea-level rise are the main objectives of ice-sheet modeling. Mass transfer from ice sheet to ocean is, in large part, through outlet glaciers. Subglacial topography plays an important role in ice dynamics; however, trough systems have not been included in bed digital elevation models (DEMS) used in modeling, because their size is close to the model resolution. Using recently collected CReSIS MCoRDs data of subglacial topography and an algorithm that allows topographically and morphologically correct integration of troughs and trough systems at any modeling scale (5 km resolution for SeaRISE), an improved Greenland bed DEM was developed that includes Jakobshavn Isbrae, Helheim, Kangerdlussuaq and Petermann glaciers (JakHelKanPet DEM). Contrasting the different responses of two Greenland ice-sheet models (UMISM and SICOPOLIS) to the more accurately represented bed shows significant differences in modeled surface velocity, basal water production and ice thickness. Consequently, modeled ice volumes for the Greenland ice sheet are significantly smaller using the JakHelKanPet DEM, and volume losses larger. More generally, the study demonstrates the role of spatial modeling of data specifically as input for dynamic ice-sheet models in assessments of future sea-level rise. - Tatsuru Sato, Ralf GreveAnnals of Glaciology 53 60 221 - 228 2012年11月 [査読有り][通常論文]
Ice-sheet modelling is an important tool for predicting the possible response of ice sheets to climate change in the past and future. An established ice-sheet model is SICOPOLIS (Simulation COde for POLythermal Ice Sheets), and for this study the previously grounded-ice-only model was complemented by an ice-shelf module. The new version of SICOPOLIS is applied to the Antarctic ice sheet, driven by standard forcings defined by the SeaRISE (Sea-level Response to Ice Sheet Evolution) community effort. A crucial point for simulations into the future is to obtain reasonable initial conditions by a palaeoclimatic spin-up, which we carry out over 125 000 years from the Eemian until today. We then carry out a set of experiments for 500 years into the future, in which the surface temperature and precipitation are kept at their present-day distributions, while sub-ice-shelf melting rates between 0 and 200 m/a are applied. These simulations show a significant, but not catastrophic, sensitivity of the ice sheet. Grounded-ice volumes decrease with increasing melting rates, and the spread of the results from the zero to the maximum melting case is similar to 0.65 m s.l.e. (metres sea-level equivalent) after 100 years and similar to 2.25 m s.l.e. after 500 years. - A. Levermann, R. Winkelmann, S. Nowicki, J. L. Fastook, K. Frieler, R. Greve, H. H. Hellmer, M. A. Martin, M. Mengel, A. J. Payne, D. Pollard, T. Sato, R. Timmermann, W. L. Wang, R. A. BindschadlerThe Cryosphere Discussions 6 3447 - 3489 2012年08月 [査読無し][通常論文]
The largest uncertainty in projections of future sea-level change still results from the potentially changing dynamical ice discharge from Antarctica. While ice discharge can alter through a number of processes, basal ice-shelf melting induced by a warming ocean has been identified as a major if not the major cause for possible additional ice flow across the grounding line. Here we derive dynamic ice-sheet response functions for basal ice-shelf melting using experiments carried out within the Sea-level Response to Ice Sheet Evolution (SeaRISE) intercomparison project with five different Antarctic ice-sheet models. As used here these response functions provide separate contributions for four different Antarctic drainage regions. Under the assumptions of linear-response theory we project future ice-discharge for each model, each region and each of the four Representative Concentration Pathways (RCP) using oceanic temperatures from 19 comprehensive climate models of the Coupled Model Intercomparison Project, CMIP-5, and two ocean models from the EU project Ice2Sea. Uncertainty in the climatic forcing, the oceanic response and the ice-model differences is combined into an uncertainty range of future Antarctic ice discharge induced from basal ice-shelf melt. The additional ice loss (Table 6) is clearly scenario-dependent and results in a median of 0.07 m (66%-range: 0.04-0.10 m; 90%-range: -0.01-0.26 m) of global sea-level equivalent for the low-emission RCP-2.6 scenario and yields 0.1 m (66%-range: 0.06-0.14 m; 90%-range: -0.01-0.45 m) for the strongest RCP-8.5. If only models with an explicit representation of ice shelves are taken into account the scenario dependence remains and the values change to: 0.05 m (66%-range: 0.03-0.08 m) for RCP-2.6 and 0.07 m (66%-range: 0.04-0.11 m) for RCP-8.5. These results were obtained using a time delay between the surface warming signal and the subsurface oceanic warming as observed in the CMIP-5 models. Without this time delay the ranges for all ice models changes to 0.10 m (66%-range: 0.07-0.12 m; 90%-range: 0.01-0.28 m) for RCP-2.6 and 0.15 m (66%-range: 0.10-0.21 m; 90%-range: 0.02-0.53 m) for RCP-8.5. All probability distributions as provided in Fig. 10 are highly skewed towards high values. - Hakime Seddik, Ralf Greve, Thomas Zwinger, Fabien Gillet-Chaulet, Olivier GagliardiniJournal of Glaciology 58 209 427 - 440 2012年06月 [査読有り][通常論文]
It is likely that climate change will have a significant impact on the mass balance of the Greenland ice sheet, contributing to future sea-level rise. Here we present the implementation of the full Stokes model Elmer/Ice for the Greenland ice sheet, which includes a mesh refinement technique in order to resolve fast-flowing ice streams and outlet glaciers. We discuss simulations 100 years into the future, forced by scenarios defined by the SeaRISE (Sea-level Response to Ice Sheet Evolution) community effort. For comparison, the same experiments are also run with the shallow-ice model SICOPOLIS (Simulation COde for POLythermal Ice Sheets). We find that Elmer/Ice is similar to 43% more sensitive (exhibits a larger loss of ice-sheet volume relative to the control run) than SICOPOLIS for the ice-dynamic scenario (doubled basal sliding), but similar to 61% less sensitive for the direct global warming scenario (based on the A1B moderate-emission scenario for greenhouse gases). The scenario with combined A1B global warming and doubled basal sliding forcing produces a Greenland contribution to sea-level rise of similar to 15 cm for Elmer/Ice and similar to 12 cm for SICOPOLIS over the next 100 years. - P. J. Applegate, N. Kirchner, E. J. Stone, K. Keller, R. GreveThe Cryosphere 6 3 589 - 606 2012年05月 [査読有り][通常論文]
Lack of knowledge about the values of ice sheet model input parameters introduces substantial uncertainty into projections of Greenland Ice Sheet contributions to future sea level rise. Computer models of ice sheet behavior provide one of several means of estimating future sea level rise due to mass loss from ice sheets. Such models have many input parameters whose values are not well known. Recent studies have investigated the effects of these parameters on model output, but the range of potential future sea level increases due to model parametric uncertainty has not been characterized. Here, we demonstrate that this range is large, using a 100-member perturbed-physics ensemble with the SICOPOLIS ice sheet model. Each model run is spun up over 125 000 yr using geological forcings and subsequently driven into the future using an asymptotically increasing air temperature anomaly curve. All modeled ice sheets lose mass after 2005 AD. Parameters controlling surface melt dominate the model response to temperature change. After culling the ensemble to include only members that give reasonable ice volumes in 2005 AD, the range of projected sea level rise values in 2100 AD is similar to 40 % or more of the median. Data on past ice sheet behavior can help reduce this uncertainty, but none of our ensemble members produces a reasonable ice volume change during the mid-Holocene, relative to the present. This problem suggests that the model's exponential relation between temperature and precipitation does not hold during the Holocene, or that the central-Greenland temperature forcing curve used to drive the model is not representative of conditions around the ice margin at this time (among other possibilities). Our simulations also lack certain observed physical processes that may tend to enhance the real ice sheet's response. Regardless, this work has implications for other studies that use ice sheet models to project or hindcast the behavior of the Greenland Ice Sheet. - Swantje Bargmann, Hakime Seddik, Ralf GreveInternational Journal for Numerical and Analytical Methods in Geomechanics 36 7 892 - 917 2012年05月 [査読有り][通常論文]
In this contribution we model flow-induced anisotropy of polar ice in order to gain a better understanding for the underlying microstructure and its influence on the deformation process. In particular, a continuum-mechanical, anisotropic flow model that is based on an anisotropic flow enhancement factor (CAFFE model) is applied. The polycrystalline ice is regarded as a mixture whose grains are characterized by their orientation. The approach is based on two distinct scales: the underlying microstructure influences the macroscopic material behavior and is taken into account phenomenologically. To achieve this, the orientation mass density is introduced as a mesoscopic field, i.e. it depends on a mesoscopic variable (the orientation) in addition to position and time. The classical flow law of Glen is extended by a scalar, but anisotropic enhancement factor. Four different effects (local rigid body rotation, grain rotation, rotation recrystallization, grain boundary migration) influencing the evolution of the grain orientations are taken into account. All modeling parameters are either measurable in or derivable from field observations or laboratory experiments. A finite volume method is chosen for the discretization procedure. Numerical results simulating the ice flow at the site of the EPICA ice core in Dronning Maud Land (referred to as EDML), Antarctica, are presented. They go beyond earlier results by Seddikit et al. (J. Glaciol. 2008; 54(187):631642) in which only local rigid body rotation and grain rotation were accounted for. By comparing simulated and observed fabrics, we come up with reference values for the parameters in the constitutive equations for rotation recrystallization and grain boundary migration. Down to 2045 m depth, good agreement can be achieved; however, further down the observed fabric cannot be reproduced well due to numerical issues. Additionally, we study the influence of the two superposed deformation regimes of vertical compression and simple shear separately and demonstrate that the numerical problems are due to the predominant shear regime near the bottom, whereas vertical compression only produces stable results everywhere. - I. Rogozhina, J. M. Hagedoorn, Z. Martinec, K. Fleming, O. Soucek, R. Greve, M. ThomasJournal of Geophysical Research: Earth Surface 117 F2 F02025 2012年05月 [査読有り][通常論文]
This study analyzes the uncertainties in the models of the Greenland Ice Sheet (GIS) that arise from ill-constrained geothermal heat flux (GHF) distribution. Within the context of dynamic GIS modeling, we consider the following questions: (i) What is the significance of the differences between the existing GHF models for the GIS modeling studies? (ii) How well does the modeled GIS controlled by the GHF models agree with the observational data? (iii) What are the relative contributions of uncertainties in GHF and climate forcing to the misfit between the observed and modeled present-day GIS? The results of paleoclimatic simulations suggest that differences in the GHF models have a major effect on the history and resulting present-day state of the GIS. The ice sheet model controlled by any of these GHF forcings reproduces the observed GIS state to only a limited degree and fails to reproduce either the topography or the low basal temperatures measured in southern Greenland. By contrast, the simulation controlled by a simple spatially uniform GHF forcing results in a considerably better fit with the observations, raising questions about the use of the three GHF models within the framework of GIS modeling. Sensitivity tests reveal that the misfit between the modeled and measured temperatures in central Greenland is mostly due to inaccurate GHF and Wisconsin precipitation forcings. The failure of the ice sheet model in southern Greenland, however, is mainly caused by inaccuracies in the surface temperature forcing and the generally overestimated GHF values suggested by all GHF models. - Heinz Blatter, Ralf Greve, Ayako Abe-OuchiSurveys in Geophysics 32 4-5 555 - 583 2011年09月 [査読有り][招待有り]
Since the late 1970s, numerical modelling has become established as an important technique for the understanding of ice sheet and glacier dynamics, and several models have been developed over the years. Ice sheet models are particularly relevant for predicting the possible response of ice sheets to climate change. Recent observations suggest that ice dynamics could play a crucial role for the contribution of ice sheets to future sea level rise under global warming conditions, and the need for further research into the matter was explicitly stated in the Fourth Assessment Report (AR4) of the United Nations Intergovernmental Panel on Climate Change (IPCC). In this paper, we review the state of the art and current problems of ice sheet and glacier modelling. An outline of the underlying theory is given, and crucial processes (basal sliding, calving, interaction with the solid Earth) are discussed. We summarise recent progress in the development of ice sheet and glacier system models and their coupling to climate models, and point out directions for future work. - Ralf Greve, Fuyuki Saito, Ayako Abe-OuchiAnnals of Glaciology 52 58 23 - 30 2011年08月 [査読有り][通常論文]
SeaRISE (Sea-level Response to Ice Sheet Evolution) is a US-led multi-model community effort to predict the likely range of the contribution of the Greenland and Antarctic ice sheets to sea-level rise over the next few hundred years under global warming conditions. The Japanese ice-sheet modelling community is contributing to SeaRISE with two large-scale, dynamic/thermodynamic models: SICOPOLIS and IcIES. Here we discuss results for the Greenland ice sheet, obtained using both models under the forcings (surface temperature and precipitation scenarios) defined by the SeaRISE effort. A crucial point for meaningful simulations into the future is to obtain initial conditions that are close to the observed state of the present-day ice sheet. This is achieved by proper tuning during model spin-up from the last glacial/interglacial cycle to today. Experiments over 500 years indicate that both models are more sensitive (exhibit a larger rate of ice-sheet mass loss) to future climate warming (based on the A1B emission scenario) than to a doubling in the basal sliding speed. Ice-sheet mass loss varies between the two models by a factor of similar to 2 for sliding experiments and a factor of similar to 3 for climate-warming experiments, highlighting the importance of improved constraints on the parameterization of basal sliding and surface mass balance in ice-sheet models. - Hakime Seddik, Ralf Greve, Thomas Zwinger, Luca PlacidiThe Cryosphere 5 2 495 - 508 2011年06月 [査読有り][通常論文]
A three-dimensional, thermo-mechanically coupled ice flow model with induced anisotropy has been applied to a similar to 200 x 200 km domain around the Dome Fuji drill site, Antarctica. The model ("Elmer/Ice") is based on the open-source multi-physics package Elmer (http://www.csc.fi/elmer/) and solves the full Stokes equations. Flow-induced anisotropy in ice is accounted for by an implementation of the Continuum-mechanical, Anisotropic Flow model, based on an anisotropic Flow Enhancement factor ("CAFFE model"). Steady-state simulations for present-day climate conditions are conducted. The main findings are: (i) the flow regime at Dome Fuji is a complex superposition of vertical compression, horizontal extension and bed-parallel shear; (ii) for an assumed geothermal heat flux of 60 mW/m2 the basal temperature at Dome Fuji reaches the pressure melting point and the basal melting rate is similar to 0.35 mm/a; (iii) in agreement with observational data, the fabric shows a strong single maximum at Dome Fuji, and the age of the ice is decreased compared to an isotropic scenario; (iv) as a consequence of spatially variable basal melting conditions, the basal age tends to be smaller where the ice is thicker and larger where the ice is thinner. The latter result is of great relevance for the consideration of a future drill site in the area. - Thorben Dunse, Ralf Greve, Thomas Vikhamar Schuler, Jon Ove HagenJournal of Glaciology 57 202 247 - 259 2011年04月 [査読有り][通常論文]
A large part of the ice flux within ice caps occurs through spatially limited fast-flowing units. Some of them permanently maintain fast flow, whereas others operate in an oscillatory mode, characterized by short-lived active phases followed by long quiescent phases. This surge-type behaviour results from intrinsic rather than external factors, thus complicating estimates of glacier response to climate change. Here we present numerical model results from Austfonna, an ice cap on Svalbard that comprises several surge-type basins. Previous studies have suggested a thermally controlled soft-bed surge mechanism for Svalbard. We systematically change the parameters that govern the nature of basal motion and thereby control the transition between permanent and oscillatory fast flow. Surge-type behaviour is realized by a relatively abrupt onset of basal sliding when basal temperatures approach the pressure-melting point and enhanced sliding of marine grounded ice. Irrespective of the dynamic regime, the absence of considerable volumes of temperate ice, both in the observed and simulated ice cap, indicates that fast flow is accomplished by basal motion over a temperate bed. Given an idealized present-day climate, the equilibrium ice-cap size varies significantly, depending on the chosen parameters. - Nina Kirchner, Ralf Greve, Arjen P. Stroeven, Jakob HeymanQuaternary Science Reviews 30 1-2 248 - 267 2011年01月 [査読有り][通常論文]
The Tibetan Plateau is a topographic feature of extraordinary dimension and has an important impact on regional and global climate. However, the glacial history of the Tibetan Plateau is more poorly constrained than that of most other formerly glaciated regions such as in North America and Eurasia. On the basis of some field evidence it has been hypothesized that the Tibetan Plateau was covered by an ice sheet during the Last Glacial Maximum (LGM). Abundant field- and chronological evidence for a predominance of local valley glaciation during the past 300,000 calendar years (that is, 300 ka), coupled to an absence of glacial landforms and sediments in extensive areas of the plateau, now refute this concept. This, furthermore, calls into question previous ice sheet modeling attempts which generally arrive at ice volumes considerably larger than allowed for by field evidence. Surprisingly, the robustness of such numerical ice sheet model results has not been widely queried, despite potentially important climate ramifications. We simulated the growth and decay of ice on the Tibetan Plateau during the last 125 ka in response to a large ensemble of climate forcings (90 members) derived from Global Circulation Models (GCMs), using a similar 3D thermomechanical ice sheet model as employed in previous studies. The numerical results include as extreme end members as an ice-free Tibetan Plateau and a plateau-scale ice sheet comparable, in volume, to the contemporary Greenland ice sheet. We further demonstrate that numerical simulations that acceptably conform to published reconstructions of Quaternary ice extent on the Tibetan Plateau cannot be achieved with the employed stand-alone ice sheet model when merely forced by paleoclimates derived from currently available GCMs. Progress is, however, expected if future investigations employ ice sheet models with higher resolution, bidirectional ice sheet-atmosphere feedbacks, improved treatment of the surface mass balance, and regional climate data and climate reconstructions. - Ralf Greve, Björn Grieger, Oliver J. StenzelPlanetary and Space Science 58 6 931 - 940 2010年05月 [査読有り][通常論文]
The Mars Atmosphere-Ice Coupler MAIC-2 is a simple, latitudinal model, which consists of a set of parameterisations for the surface temperature, the atmospheric water transport and the surface mass balance (condensation minus evaporation) of water ice. It is driven directly by the orbital parameters obliquity, eccentricity and solar longitude (Ls) of perihelion. Surface temperature is described by the Local Insolation Temperature (LIT) scheme, which uses a daily and latitude-dependent radiation balance. The evaporation rate of water is calculated by an expression for free convection, driven by density differences between water vapor and ambient air, the condensation rate follows from the assumption that any water vapour which exceeds the local saturation pressure condenses instantly, and atmospheric transport of water vapour is approximated by instantaneous mixing. Glacial flow of ice deposits is neglected. Simulations with constant orbital parameters show that low obliquities favour deposition of ice in high latitudes and vice versa. A transient scenario driven by a computed history of orbital parameters over the last 10 million years produces essentially monotonically growing polar ice deposits during the most recent 4 million years, and a very good agreement with the observed present-day polar layered deposits. The thick polar deposits sometimes continue in thin ice deposits which extend far into the mid latitudes, which confirms the idea of "ice ages" at high obliquity. - Luca Placidi, Ralf Greve, Hakime Seddik, Sergio H. FariaContinuum Mechanics and Thermodynamics 22 3 221 - 237 2010年03月 [査読有り][通常論文]
A complete theoretical presentation of the Continuum-mechanical, Anisotropic Flow model, based on an anisotropic Flow Enhancement factor (CAFFE model) is given. The CAFFE model is an application of the theory of mixtures with continuous diversity for the case of large polar ice masses in which induced anisotropy occurs. The anisotropic response of the polycrystalline ice is described by a generalization of Glen's flow law, based on a scalar anisotropic enhancement factor. The enhancement factor depends on the orientation mass density, which is closely related to the orientation distribution function and describes the distribution of grain orientations (fabric). Fabric evolution is governed by the orientation mass balance, which depends on four distinct effects, interpreted as local rigid body rotation, grain rotation, rotation recrystallization (polygonization) and grain boundary migration (migration recrystallization), respectively. It is proven that the flow law of the CAFFE model is truly anisotropic despite the collinearity between the stress deviator and stretching tensors. - Yoshinori Iizuka, Hideki Miura, Shogo Iwasaki, Hideaki Maemoku, Takanobu Sawagaki, Ralf Greve, Hiroshi Satake, Kimikazu Sasa, Yuki MatsushiJournal of Glaciology 56 197 395 - 404 2010年 [査読有り][通常論文]
Ice originating near the inland ice divide of the ice sheet can reappear as marginal ice at the surface near the ice terminal in the ablation area. We have analyzed delta-18-O values and ion concentrations of the Skallen, Skarvsnes and Hamna terminal ice sections, located along the estuary line in the Soya drainage basin, East Antarctica. The data suggest that the upper part of the Skallen terminal ice section could have originated from inland precipitation on the Shirase drainage basin during marine isotope stage (MIS) 5e, while the upper part of Skarvsnes and Hamna terminal ice sections could have originated from inland precipitation on the Soya drainage basin. We calculate past elevation maps for the Antarctic ice sheet using the three-dimensional model, SICOPOLIS. This model suggests that the upstream portion of the Soya drainage basin during the glacial period (MIS 2, 3 or 4) was located to the northeast of its present location. A flow history is proposed wherein ice from the inland Shirase drainage area flowed over the present ice-divide line from the Shirase to the Soya drainage basin during the glacial period. The ice in the Soya drainage basin then flowed to the marginal part of the sheet after the ice divide had assumed its present position. - Heinz Blatter, Ralf Greve, Ayako Abe-OuchiJournal of Glaciology 56 200 1087 - 1094 2010年 [査読有り][招待有り]
Observations of glacier flow and explanations of its origin started as early as the 18th century. Several mechanisms were suggested before gravity-driven viscous flow became the accepted theory of glacier flow in the 1950s, the early years of the Journal of Glaciology. Since the viscosity of ice is strongly temperature-dependent, the topic of glacier and ice-sheet dynamics became essentially a fluid-dynamical problem. The availability of growing computing power turned the field of glacier mechanics and thermodynamics into a field of numerical modelling with increasing sophistication. - Reinhard Calov, Ralf Greve, Ayako Abe-Ouchi, Ed Bueler, Philippe Huybrechts, Jesse V. Johnson, Frank Pattyn, David Pollard, Catherine Ritz, Fuyuki Saito, Lev TarasovJournal of Glaciology 56 197 371 - 383 2010年 [査読有り][通常論文]
Results from the Heinrich Event INtercOmparison (HEINO) topic of the Ice-Sheet Model Intercomparison Project (ISMIP) are presented. ISMIP HEINO was designed to explore internal large-scale ice-sheet instabilities in different contemporary ice-sheet models. These instabilities are of interest because they are a possible cause of Heinrich events. A simplified geometry experiment reproduces the main characteristics of the Laurentide ice sheet, including the sedimented region over Hudson Bay and Hudson Strait. The model experiments include a standard run plus seven variations. Nine dynamic/thermodynamic ice-sheet models were investigated; one of these models contains a combination of the shallow-shelf (SSA) and shallow-ice approximation (SIA), while the remaining eight models are of SIA type only. Seven models, including the SIA-SSA model, exhibit oscillatory surges with a period of similar to 1000 years for a broad range of parameters, while two models remain in a permanent state of streaming for most parameter settings. In a number of models, the oscillations disappear for high surface temperatures, strong snowfall and small sediment sliding parameters. In turn, low surface temperatures and low snowfall are favourable for the ice-surge cycles. We conclude that further improvement of ice-sheet models is crucial for adequate, robust simulations of cyclic large-scale instabilities. - Ralf Greve, Luca Placidi, Hakime Seddik低温科学 68 (Suppl.) 137 - 148 低温科学研究所 2009年12月 [査読無し][招待有り]
In order to study the mechanical behaviour of polar ice masses, the method of continuum mechanics is used. The newly developed CAFFE model (Continuum-mechanical, Anisotropic Flow model, based on an anisotropic Flow Enhancement factor) is described, which comprises an anisotropic flow law as well as a fabric evolution equation. The flow law is an extension of the isotropic Glen's flow law, in which anisotropy enters via an enhancement factor that depends on the deformability of the polycrystal. The fabric evolution equation results from an orientational mass balance and includes constitutive relations for grain rotation and recrystallization. The CAFFE model fulfills all the fundamental principles of classical continuum mechanics, is sufficiently simple to allow numerical implementations in ice-flow models and contains only a limited number of free parameters. The applicability of the CAFFE model is demonstrated by a case study for the site of the EPICA (European Project for Ice Coring in Antarctica) ice core in Dronning Maud Land, East Antarctica. - Ralf Greve, Shin SugiyamaArXiv E-Prints arXiv:0905.2027 2009年05月 [査読無し][通常論文]
Simulations of the Greenland Ice Sheet are carried out with a high-resolution version of the ice-sheet model SICOPOLIS for several global-warming scenarios for the period 1990-2350. In particular, the impact of surface-meltwater-induced acceleration of basal sliding on the stability of the ice sheet is investigated. A parameterization for the acceleration effect is developed for which modelled and measured mass losses of the ice sheet in the early 21st century agree well. The main findings of the simulations are: (i) the ice sheet is generally very susceptible to global warming on time-scales of centuries, (ii) surface-meltwater-induced acceleration of basal sliding leads to a pronounced speed-up of ice streams and outlet glaciers, and (iii) this ice-dynamical effect accelerates the decay of the Greenland Ice Sheet as a whole significantly, but not catastrophically, in the 21st century and beyond. - Hakime Seddik, Ralf Greve, Shin Sugiyama, Renji NaruseArXiv E-Prints arXiv:0901.1177 2009年01月 [査読無し][通常論文]
A numerical model was developed for simulating the formation of U-shaped glacial valleys by coupling a two-dimensional ice flow model with an erosion model for a transverse cross section. The erosion model assumes that the erosion rate varies quadratically with sliding speed. We compare the two-dimensional model with a simple shallow-ice approximation model and show the differences in the evolution of a pre-glacial V-shaped valley profile using the two models. We determine the specific role of the lateral shear stresses acting on the glacier side walls in the formation of glacial valleys. By comparing the model results with field data, we find that U-shaped valleys can be formed within 50 ka. A shortcoming of the model is that it primarily simulates the formation of glacial valleys by deepening, whereas observed valleys apparently have formed mainly by widening. - Angelika Humbert, Thomas Kleiner, Chris-Oliver Mohrholz, Christoph Oelke, Ralf Greve, Manfred A. LangeJournal of Glaciology 55 189 53 - 65 2009年 [査読有り][通常論文]
Two diagnostic, dynamic/thermodynamic ice-shelf models are applied to the Brunt Ice Shelf/Stancomb-Wills Ice Tongue system, located off Caird Coast, Coats Land, Antarctica. The Brunt Ice Shelf/Stancomb-Wills Ice Tongue system is characterized as a thin, unbounded ice shelf with an atypical and highly heterogeneous structure. In contrast to other ice shelves, a composite mass of icebergs that calved at the grounding line and were then locked within fast (sea) ice exists between the fast-moving Stancomb-Wills Ice Stream and the slow-moving Brunt Ice Shelf. We simulate the present flow regime of the ice shelf that results from the ice-thickness distribution and the inflow at the grounding line with two different models, and compare the model results with feature tracking and InSAR flow velocities. We then incorporate two observed features, a rift and a shear margin, into the models with two different approaches, and demonstrate the effects of variations in numerical values for the shear strength and viscosity in these zones on the simulated velocity field. A major result is that both kinds of implementation of the rifts lead to similar effects on the entire velocity field, while there are discrepancies in the vicinity of the rifts. - Ralf GreveProceedings of the First International Symposium on the Arctic Research (ISAR-1) 90 - 93 2008年11月 [査読無し][通常論文]
- Swantje Bargmann, Ralf Greve, Paul SteinmannBulletin of Glaciological Research 26 23 - 32 2008年08月 [査読有り][通常論文]
In 2005, the Cassini spacecraft proved the existence of cryovolcanism, i.e., the icy counterpart of volcanism on Earth, on Saturn's moon Enceladus during its close fly-bys. In particular, water-rich plume venting was discovered in the south polar region. Thus, Enceladus was found to be one out of three outer solar bodies to be geologically active. This contribution is concerned with the modeling and computation of this phenomenon. For the underlying thermoelastic description of ice at cryogenic temperatures, we resort to the Green-Naghdi approach. The Green-Naghdi theory includes the classical Fourier approach, but, in addition to that, it is a lot more general as it also allows for other types of heat propagation. The numerical implementation is carried out with the help of the finite element method. Results show that lateral spreading of internal and surface warming away from an active volcanic vent increases strongly with increasing contribution of the non-classical heat flux. Agreement with available high-resolution surface temperature data based on infrared spectrometry seems to be best if the non-classical heat flux contributes significantly to the total heat transport. Complementary laboratory studies would be required in order to strengthen this speculative, yet promising idea. - Ralf GreveIcarus 196 2 359 - 367 2008年08月 [査読有り][通常論文]
The Martian polar caps feature large chasmata and smaller trough systems which have no counterpart in terrestrial ice sheets. Chasma Boreale cuts about 500 km into the western part of the north-polar cap, is up to 100 km wide and up to 2 km deep. One possible formation mechanism is by a temporary heat source under the ice due to tectonothermal or volcanic activity, which melts the ice from below. It is demonstrated by model simulations that this process is feasible, a moderately increased heat flux of 0.5–1 W/m^2, sustained over at least tens of thousands of years, producing a topographic depression which resembles the real chasma. Associated meltwater discharge rates are small (< 1 km^3/a), but can exceed 10 km^3/a if a stronger heat flux of 10 W/m^2 is assumed. Local ice-flow velocities during the process of chasma formation can exceed 1 m/a at the head and scarps of the chasma. However, if the thermal anomaly shuts down, glacial flow quickly decreases, so that the chasma can stay open for an indefinite amount of time without an ongoing, sustaining process under the climate conditions of the most recent millions of years. - Hakime Seddik, Ralf Greve, Luca Placidi, Ilka Hamann, Olivier GagliardiniJournal of Glaciology 54 187 631 - 642 2008年 [査読有り][通常論文]
We present an application of the newly developed CAFFE model (Continuum-mechanical, Anisotropic Flow model based on an anisotropic Flow Enhancement factor) to the EPICA ice core at Kohnen Station, Dronning Maud Land, Antarctica (referred to as the EDML core). A one-dimensional flow model for the site is devised, which includes the anisotropic flow law and the fabric evolution equation of the CAFFE model. Three different solution methods are employed: (1) computing the ice flow based on the flow law of the CAFFE model and the measured fabrics; (2) solving the CAFFE fabric evolution equation under the simplifying assumption of transverse isotropy; and (3) solving the unrestricted CAFFE fabric evolution equation. Method (1) demonstrates clearly the importance of the anisotropic fabric in the ice column for the flow velocity. The anisotropic enhancement factor produced with method (2) agrees reasonably well with that of method (1), even though the measured fabric shows a girdle structure (which breaks the transverse isotropy) in large parts of the ice core. For method (3), we find that the measured fabric is reproduced well by the model down to similar to 2100 m depth. Systematic deviations at greater depths are attributed to the disregard of migration recrystallization in the model. - Ralf Greve低温科学 66 139 - 148 低温科学研究所 2007年12月 [査読無し][招待有り]
Both Martian polar regions are covered by prominent ice caps. Similar to snow on Earth, the seasonal caps are extended layers of CO2 frost which grow and shrink over the seasons. In the respective summer season, much smaller permanent caps remain, which are underlain by 3 km high topographic domes termed as polar layered deposits. The polar layered deposits consist mainly of H2O ice and have formed by exchange of water with the atmosphere over at least millions of years. Alternating layers of clear and dusty ice, which are exposed in surface troughs and close to the margin, indicate a complex climatic history of Mars driven by quasiperiodic changes of orbital elements, similar to the Milankovitch cycles on Earth. Likely present-day glacial flow velocities are of the order of 0.1-1 mm/a, the north polar deposits being more dynamic than the southern ones due to higher surface temperatures. Basal temperatures are far below the pressure melting point, with the possible exception of geothermally active areas under the ice. - O. J. Stenzel, B. Grieger, H. U. Keller, R. Greve, K. Fraedrich, E. Kirk, F. LunkeitPlanetary and Space Science 55 14 2087 - 2096 2007年11月 [査読有り][通常論文]
A general circulation model of the Martian Atmosphere is coupled with a 3-dimensional polythermal ice-sheet model of the polar ice caps. With this combination a series of experiments is carried out to investigate the impact of long-term obliquity change on the Martian north polar ice cap (NPC). The behaviour of the NPC is tested under obliquities of θ=15°, 25° and 35°. With increasing obliquity the area covered by the NPC gets smaller but does not vanish. However, when started from an ice-free condition the models develop an ice cap only for low obliquities. The ‘critical’ obliquity at which a build-up of a new polar cap is possible is θ=22°. - Ralf Greve, Shoko OtsuThe Cryosphere Discussions 1 41 - 76 2007年06月 [査読無し][通常論文]
The north-east Greenland ice stream (NEGIS) was discovered as a large fast-flow feature of the Greenland ice sheet by synthetic aperture radar (SAR) imaginary of the ERS-1 satellite. In this study, the NEGIS is implemented in the dynamic/thermodynamic, large-scale ice-sheet model SICOPOLIS (Simulation Code for POLythermal Ice Sheets). In the first step, we simulate the evolution of the ice sheet on a 10-km grid for the period from 250 ka ago until today, driven by a climatology reconstructed from a combination of present-day observations and GCM results for the past. We assume that the NEGIS area is characterized by enhanced basal sliding compared to the "normal", slowly-flowing areas of the ice sheet, and find that the misfit between simulated and observed ice thicknesses and surface velocities is minimized for a sliding enhancement by the factor three. In the second step, the consequences of the NEGIS, and also of surface-meltwater-induced acceleration of basal sliding, for the possible decay of the Greenland ice sheet in future warming climates are investigated. It is demonstrated that the ice sheet is generally very susceptible to global warming on time-scales of centuries and that surface-meltwater-induced acceleration of basal sliding can speed up the decay significantly, whereas the NEGIS is not likely to dynamically destabilize the ice sheet as a whole. - Thomas Zwinger, Ralf Greve, Olivier Gagliardini, Takayuki Shiraiwa, Mikko LylyAnnals of Glaciology 45 29 - 37 2007年 [査読有り][通常論文]
The Gorshkov crater glacier at Ushkovsky volcano, Kamchatka, is characterized by a large aspect ratio and special thermodynamic conditions at the bedrock caused by a locally enhanced and spatially varying geothermal heat flux. Furthermore, large parts of this glacier consist of firn rather than pure ice, which alters the rheological properties (such as viscosity and compressibility) of the glacier. We present a newly developed, thermo-mechanically coupled, three-dimensional flow model based on the finite-element (FE) modeling software Elmer, and apply it to the Gorshkov crater glacier. By assuming steady-state conditions, the present-day velocity field, temperature field, basal melting rate and age distribution are simulated. We find that flow velocities are generally small (tens of centimeters per year). Horizontal and vertical velocities are of comparable magnitude, which shows that the shallow-ice approximation is not applicable. Owing to the spatially variable volcanic heat flux, the thermal regime at the ice base is cold in the deeper parts of the glacier and temperate in the shallower parts. The measured temperature profile and age horizons at the K2 borehole are reproduced quite well, and remaining discrepancies may be attributed to transient (non-steady-state) conditions. Firn compressibility is identified as a crucial element for the modeling approach. - Ralf Greve, Ryoji Takahama, Reinhard CalovPolar Meteorology and Glaciology 20 1 - 15 2006年11月 [査読有り][通常論文]
The three-dimensional, dynamic/thermodynamic ice-sheet model SICOPOLIS (SImulation COde for POLythermal Ice Sheets) is applied to the ISMIP HEINO (Ice Sheet Model Intercomparison Project-Heinrich Event INtercOmparison) set-up. ISMIP HEINO has been designed to study large-scale ice-sheet instabilities, similar to those of the Laurentide ice sheet which are likely the cause of Heinrich events, on a simplified geometry which consists of a flat square with 4000 km side length. This square contains an area which resembles Hudson Bay and Hudson Strait, on which rapid sediment sliding can occur. The ice sheet is built up over 200 ka by assuming a temporally constant glacial climate. For the standard set-up of ISMIP HEINO, we obtain an oscillatory behaviour of the ice sheet with a main period of approx. 7.5 ka. One cycle consists of a gradual growth phase, followed by a massive surge through "Hudson Bay" and "Hudson Strait" owing to rapid sediment sliding on a molten bed. The occurrence of internal oscillations is robust against moderate variations of the surface boundary conditions and the strength of the sediment sliding. These findings support the idea of a free oscillatory mechanism as the main cause for large-scale ice-sheet surges. - Ralf GreveGAMM-Mitteilungen 29 1 29 - 51 2006年04月 [査読有り][招待有り]
The role of water ice in the solar system is reviewed from a fluid‐dynamical point of view. On Earth and Mars, water ice forms ice sheets, ice caps and glaciers at the surface, which show glacial flow under their own weight. By contrast, water ice is a major constituent of the bulk volume of the icy satellites in the outer solar system, and ice flow can occur as thermal convection. The rheology of polycrystalline aggregates of ordinary, hexagonal ice Ih is described by a power law, different forms of which are discussed. The temperature dependence of the ice viscosity follows an Arrhenius law. Therefore, the flow of ice in a planetary environment constitutes a thermo‐mechanically coupled problem; its model equations are obtained by inserting the flow law and the thermodynamic material equations in the balance laws of mass, momentum and energy. As an example of gravity‐driven flow, the polar caps of Mars are discussed. For the north‐polar cap, large‐scale flow velocities of the order of 0.1 … 1 mm/a are likely, locally enhanced by a factor ten or more in the vicinity of surface scarps/troughs. By contrast, the colder south‐polar cap is expected to be almost stagnant. Tidally heated convection is discussed for the example of the icy crust of Europa, where a two‐dimensional model predicts the formation of an upper, conductive lid and a lower, convective layer with flow velocities of the order of 100 mm/a. Very little is known about the fluid‐dynamical relevance of high‐pressure phases of water ice as well as ices made up of other materials. - Angelika Humbert, Ralf Greve, Kolumban HutterJournal of Geophysical Research: Earth Surface 110 F4 F04022 2005年12月 [査読有り][通常論文]
The diagnostic, dynamic/thermodynamic ice shelf model Finite Element Shallow Shelf Approximation Code (FESSACODE) is applied to the Ross Ice Shelf. We simulate the present ice flow which results from the ice thickness distribution, the inflow at the grounding line, and the surface and bottom temperatures and compare results with measured flow velocities. Our reference simulation reproduces the general flow pattern and the magnitudes of the flow velocities reasonably well. The ice flow is found to be very sensitive to the flow enhancement factor, the ice thickness, and the ice temperature but robust against inflow velocities from ice streams, glaciers, and ice rises. The ice rises (Roosevelt Island and Crary Ice Rise) stabilize the ice shelf by significantly decreasing the flow velocities for the entire ice shelf area. The ice shelf is susceptible to global warming in that a 2°C surface warming entails an increase of the flow velocities by a factor 1.25, whereas a 10°C warming leads to an increase by a factor 3.1. - J. Segschneider, B. Grieger, H. U. Keller, F. Lunkeit, E. Kirk, K. Fraedrich, A. Rodin, R. GrevePlanetary and Space Science 53 6 659 - 670 2005年05月 [査読有り][通常論文]
A climate model of intermediate complexity, named the Mars Climate Simulator, has been developed based on the Portable University Model of the Atmosphere (PUMA). The main goal of this new development is to simulate the climate variations on Mars resulting from the changes in orbital parameters and their impact on the layered polar terrains (also known as permanent polar ice caps). As a first step towards transient simulations over several obliquity cycles, the model is applied to simulate the dynamical and thermodynamical response of the Martian climate system to different but fixed obliquity angles. The model is forced by the annual and daily cycle of solar insolation. Experiments have been performed for obliquities of φ=15° (minimum), φ=25.2° (present), and φ=35° (maximum). The resulting changes in solar insolation mainly in the polar regions impact strongly on the cross-equatorial circulation which is driven by the meridional temperature gradient and steered by the Martian topography. At high obliquity, the cross-equatorial near surface flow from the winter to the summer hemisphere is strongly enhanced compared to low obliquity periods. The summer ground temperature ranges from 200 K (φ=15°) to 250 K (φ=35°) at 80°N in northern summer, and from 220 K (φ=15°) to 270 K (φ=35°) at 80°S in southern summer. In the atmosphere at 1 km above ground, the respective range is 195–225 K in northern summer, and 210–250 K in southern summer. - Reinhard Calov, Andrey Ganopolski, Martin Claussen, Vladimir Petoukhov, Ralf GreveClimate Dynamics 24 6 545 - 561 2005年05月 [査読有り][通常論文]
We study the mechanisms of glacial inception by using the Earth system model of intermediate complexity, CLIMBER-2, which encompasses dynamic modules of the atmosphere, ocean, biosphere and ice sheets. Ice-sheet dynamics are described by the three-dimensional polythermal ice-sheet model SICOPOLIS. We have performed transient experiments starting at the Eemiam interglacial, at 126 ky BP (126,000 years before present). The model runs for 26 kyr with time-dependent orbital and CO2 forcings. The model simulates a rapid expansion of the area covered by inland ice in the Northern Hemisphere, predominantly over Northern America, starting at about 117 kyr BP. During the next 7 kyr, the ice volume grows gradually in the model at a rate which corresponds to a change in sea level of 10 in per millennium. We have shown that the simulated glacial inception represents a bifurcation transition in the climate system from an interglacial to a glacial state caused by the strong snow-albedo feedback. This transition occurs when summer insolation at high latitudes of the Northern Hemisphere drops below a threshold value, which is only slightly lower than modern summer insolation. By performing long-term equilibrium runs, we find that for the present-day orbital parameters at least two different equilibrium states of the climate system exist-the glacial and the interglacial; however, for the low summer insolation corresponding to 115 kyr BP, we find only one, glacial, equilibrium state, while for the high summer insolation corresponding to 126 kyr BP only an interglacial state exists in the model. - Ralf Greve, Rupali A. MahajanIcarus 174 2 475 - 485 2005年04月 [査読有り][通常論文]
The evolution and dynamics of the north-polar cap (residual-ice-cap/layered-deposits complex) of Mars is simulated with a thermomechanical ice-sheet model. We consider a scenario with ice-free initial conditions at 5 Ma before present due to the large obliquities which prevailed prior to this time. The north-polar cap is then built up to its present shape, driven by a parameterized climate forcing (surface temperature, surface mass balance) based on the obliquity and eccentricity history. The effects of different ice rheologies and different dust contents are investigated. It is found that the build-up scenarios require an accumulation rate of approximately 0.15-0.2 mm/a at present. The topography evolution is essentially independent of the ice dynamics due to the slow ice flow. Owing to the uncertainties associated with the ice rheology and the dust content, flow velocities can only be predicted within a range of two orders of magnitude. Likely present values are of the order of 0.1-1 mm/a and a strong variation over the climatic cycles is found. For all cases, Computed basal temperatures are far below pressure melting. - Reinhard Calov, Ralf GreveJournal of Glaciology 51 172 173 - 175 2005年 [査読有り][通常論文]
- Ralf GreveAnnals of Glaciology 42 424 - 432 2005年 [査読有り][通常論文]
The thermomechanical, three-dimensional ice-sheet model SICOPOLIS is applied to the Greenland ice sheet. Simulations over two glacial-interglacial cycles are carried out, driven by a climatic forcing interpolated between present conditions and Last Glacial Maximum anomalies. Based on the global heat-flow representation by Pollack and others (1993), we attempt to constrain the spatial pattern of the geothermal heat flux by comparing simulation results to direct measurements of basal temperatures at the GRIP, NorthGRIP, Camp Century and Dye 3 ice-core locations. The obtained heat-flux map shows an increasing trend from west to east, a high-heat-flux anomaly around NorthGRIP with values up to 135 mW/m^2 and a low-heat-flux anomaly around Dye 3 with values down to 20 mW/m^2. Validation is provided by the generally good fit between observed and measured ice thicknesses. Residual discrepancies are most likely due to deficiencies of the input precipitation rate and further variability of the geothermal heat flux not captured here. - Ralf Greve, Ryoji TakahamaProceedings of the 6th International Conference on Global Change: Connection to the Arctic (GCCA-6), Miraikan, Tokyo, Japan 160 - 163 2005年 [査読無し][通常論文]
- Ralf Greve, Rupali A. Mahajan, Joachim Segschneider, Björn GriegerPlanetary and Space Science 52 9 775 - 787 2004年08月 [査読有り][通常論文]
Celestial-mechanical Computations show that, even stronger than for Earth, Mars is subject to Milankovic cycles, that is, quasi-periodic variations of the orbital parameters obliquity, eccentricity and precession. Consequently, solar insolation varies on time-scales of 10^4-10^5 years. It has long been supposed that this entails climatic cycles like the terrestrial glacial-interglacial cycles. This hypothesis is supported by the light-dark layered deposits of the north- and south-polar caps indicating a strongly varying dust content of the ice due to varying climate conditions in the past. This study aims at simulating the dynamic and thermodynamic evolution of the north-polar cap (NPC) of Mars with the ice-sheet model SICOPOLIS. The boundary conditions of surface accumulation, ablation and temperature are derived directly from the solar-insolation history by applying the newly developed model MAIC. We consider steady-state scenarios under present climate conditions as well as transient scenarios over climatic cycles. It is found that the NPC is most likely not in steady state with the present climate. The topography of the NPC is mainly controlled by the history of the surface mass balance. Ice flow, which is of the order of 1 mm/a, plays only a minor role. In order to build up the present cap during the last five million years of relatively low obliquities, a present accumulation rate of greater than or equal to 0.25 mm/a water equiv. is required. Computed basal temperatures are far below pressure melting for all simulations and all times. - Pirjo-Leena Forsström, Ralf GreveGlobal and Planetary Change 42 1-4 59 - 81 2004年07月 [査読有り][通常論文]
The Eurasian Weichselian glaciation is studied with the SICOPOLIS ice-sheet model and UKMO PMIP climate anomaly forcings. A set of sensitivity tests are completed, including runs in cold-ice mode, different positive-degree-day (PDD) factors and modified climatic data-sets. The model set-up with present-day climatology modified by a glacial index brings forth an areally correct Last Glacial Maximum (LGM) extent in the western areas, but the ice-sheet volume is too small compared to reconstructions from rebound rates. Applying modified climate data results in similar extent as indicated by the Quaternary Environment of the Eurasian North (QUEEN) Late Weichselian ice-sheet reconstruction. The simulation results display freshwater fluxes from melting and calving in phase with Heinrich events H3 at 27, H2 at 22, and HI at 14 ka ago. These peaks correspond to fast flow areas, with main activity at 27 and 22 ka ago in the Nordic Channel area and later in the Bear Island and Storfjorden region. The activity of these areas seems to be shifting from south to north from LGM to the Holocene. The freshwater pulse at 19-18.5 ka could correspond to Dansgaard-Oeschger oscillation, as well as ice volume flux peaks around 18-17 ka ago on the western margin of the ice sheet. - Ute C. Herzfeld, Garry K. C. Clarke, Helmut Mayer, Ralf GreveComputers & Geosciences 30 3 291 - 302 2004年04月 [査読有り][通常論文]
Crevasse patterns are the writings in a glacier's history book - the movement, strain and deformation frozen in ice. Therefore by analysis of crevasse patterns we can learn about the ice-dynamic processes which the glacier has experienced. Direct measurement of ice movement and deformation is time-consuming and costly, in particular for large glaciers; typically, observations are lacking when sudden changes occur. Analysis of crevasse patterns provides a means to reconstruct past and ongoing deformation processes quantitatively. This is especially important for fast-moving ice. Ice movement and deformation are commonly described and analyzed using continuum mechanics and measurements of ice velocities or strain rates. Here, we present a different approach to the study of ice deformation based on principles of structural geology. Fast ice movement manifests itself in the occurrence of crevasses. Because crevasses remain after the deformation event and may be transported, overprinted or closed, their analysis based on aerial videography and photography or satellite data gives information on past deformation events and resulting strain states. In our treatment, we distinguish (A) continuously fast-moving glaciers and ice streams, and (B) surge-type glaciers, based on observations of two prototypes, (A) Jakobshavn Isbrae, Greenland, and (B) Bering Glacier, Alaska, during the 1993-1995 surge. Classes of ice-deformation types are derived from aerial images of ice surfaces using structural glaciology. For each type, the deformation gradient matrix is formed. Relationships between invariants used in structural geology and continuum mechanics and the singular value decomposition are established and applied to ice-surface classification. Deformation during a surge is mostly one of the extensional deformation types. Continuously, or infinitesimally repeated, deformation acting in continuously fast-moving ice causes typical crevasse patterns. The structural-geology approach also includes a way to treat the problem of shear, as observed in the margins of fast-moving ice streams in slow-moving surrounding ice. In this paper we provide a first link between a physical analysis of ice-surface deformation and a connectionist-geostatistical analysis of the same problem. - Ralf GreveProceedings of the 5th International Workshop on Global Change: Connection to the Arctic (GCCA-5), University of Tsukuba, Japan 42 - 45 2004年 [査読無し][通常論文]
- Ralf Greve, Volker Klemann, Detlef WolfPlanetary and Space Science 51 3 193 - 204 2003年03月 [査読有り][通常論文]
The flow of the north polar cap of Mars, which is assumed to consist mainly of H2O ice, is investigated with the three-dimensional ice-sheet model SICOPOLIS. We consider a simplified topography and a climatic forcing varying between the present state and warmer, more humid conditions in the past with an obliquity cycle of 1.3 million earth years (yr). Furthermore, SICOPOLIS is coupled with the three-layer viscoelastic ground model displace to simulate the isostatic response of the underlying lithosphere/mantle system. Likely ice-flow velocities at present are a few mm/yr, along with surface accumulation/ablation rates of the order of 0.1 mm water equiv./yr and basal temperatures more than 50°C below pressure melting. Thicknesses of the theological lithosphere of 50-400 km are consistent with geothermal heat fluxes of 15-36 mW/m^2, with some evidence for values of ca. 80-120 km and 20-30 mW/m^2, respectively. For an Earth-like upper-mantle Viscosity of O(10^(21) Pa s), relaxation times of the lithosphere/mantle system are much shorter than significant load changes, so that the mantle behaves as an inviscid fluid. The poor correlation between the computed and measured free-air gravity signal indicates that it is determined by mass anomalies of a different origin. - Pirjo-Leena Forsström, Olli Sallasmaa, Ralf Greve, Thomas ZwingerAnnals of Glaciology 37 383 - 389 2003年 [査読有り][通常論文]
In order to reconstruct the palaeoglaciation in Fermoscandia and northern Asia during the late-Weichselian ice-age phase, simulations with the dynamic and thermodynamic ice-sheet model SICOPOLIS are carried out. Our focus is on the Last Glacial Maximum (LGM) around 20 kyr BP. Climate forcing is based on mean annual surface temperature and precipitation derived from present data and Palaeoclimatic Modelling Intercomparison Project (PMIP) UKMO21 results for the LGM. These distributions are interpolated via a glacial index defined by the Greenland Icecore Project (GRIP) δ18O record. The extent of the Scandinavian and the Barents ice sheets is reproduced in good agreement with the Quaternary Environments of the Eurasian North (QUEEN) reconstruction, but the Kara Sea and Taymyr Peninsula areas are excessively glaciated. The fast-flow regions derived from the simulations, which are generally connected to regions with a temperate base and temperate ice above, are compared to hypothesized palaeo-ice-stream locations, especially in the Norwegian Channel and the Baltic area. In the Norwegian Channel, temperate basal conditions with temperate ice above prevail and favour fast flow. In the Baltic area, ice-sheet advance is generally accompanied by slow ice velocities (<200 m/a). Some temporary fast-flow features occur due to transitional temperate-base conditions, and higher velocities arise in retreat phases. - Reinhard Calov, Andrey Ganopolski, Vladimir Petoukhov, Martin Claussen, Ralf GreveGeophysical Research Letters 29 24 2216 2002年12月 [査読有り][通常論文]
Heinrich events, related to large-scale surges of the Laurentide ice sheet, represent one of the most dramatic types of abrupt climate change occurring during the last glacial. Here, using a coupled atmosphere-ocean-biosphere-ice sheet model, we simulate quasi-periodic large-scale surges from the Laurentide ice sheet. The average time between simulated events is about 7,000 yrs, while the surging phase of each event lasts only several hundred years, with a total ice volume discharge corresponding to 5-10 m of sea level rise. In our model the simulated ice surges represent internal oscillations of the ice sheet. At the same time, our results suggest the possibility of a synchronization between instabilities of different ice sheets, as indicated in paleoclimate records. - Ralf Greve, Reinhard CalovJournal of Computational Physics 179 2 649 - 664 2002年07月 [査読有り][通常論文]
A general finite-difference marching scheme for the numerical solution of the ice-thickness equation in ice sheets is considered. From this scheme, a variety of explicit, ADI, implicit and over-implicit methods can be derived. These methods are compared for stability and accuracy within the dynamic/thermodynamic ice-Sheet model SICOPOLIS for two different problems: (i) a simple axi-symmetric steady-state ice sheet which rests on a flat bedrock, and (ii) the time-dependent paleo-glaciation of the northern hemisphere. As expected, over-implicit methods turn out to be most stable. For the simple problem, all schemes provide a good accuracy, whereas for the northern hemisphere simulations, the accuracy of the over-implicit scheme is not satisfactory, so that the implicit technique without over-weighing appears favorable for this application. - Ralf Greve, Yongqi Wang, Bernd MüggeAnnals of Glaciology 35 487 - 494 2002年 [査読有り][通常論文]
A one-dimensional model problem for computation of the age field in ice sheets, which is of great importance for dating deep ice cores, is considered. The corresponding partial differential equation (PDE) is of purely advective (hyperbolic) type, which is notoriously difficult to solve numerically. By integrating the PDE over a space-time element in the sense of a finite-volume approach, a general difference equation is constructed from which a hierarchy of solution schemes can be derived. Iteration rules are given explicitly for central differences, first-, second- and third-order (QUICK) upstreaming as well as modified TVD Lax-Friedrichs schemes (TVDLFs). The performance of these schemes in terms of convergence and accuracy is discussed. Second-order upstreaming, the modified TVDLF scheme with Minmod slope limiter and, with limitations of the accuracy directly at the base, first-order upstreaming prove to be the most suitable for numerical age computations in ice-sheet models. - Dambaru R. Baral, Kolumban Hutter, Ralf GreveApplied Mechanics Reviews 54 3 215 - 256 2001年05月 [査読有り][通常論文]
A review is given of the theory of polythermal ice sheets, ie, ice masses of which the ice has submelting temperatures in certain subdomains and is at the pressure melting point in other subdomains. Cold ice is treated as a non-linearly viscous heat conducting fluid, temperate ice as a mixture of ice at the melting point and melt-water diffusing through the ice matrix. Cold and temperate ice are separated by a non-material singular Stefan-type surface. We repeat and partly amend the complicated field equations and boundary conditions as derived in the literature. These equations are subjected to a scale analysis that makes the creeping flow conditions and the shallow geometries of land-based ice sheets explicit. The small aspect ratio ε — typical depth to horizontal distance over which the geometry and/or stresses change appreciably — suggests a perturbation approach for a possible analytical or numerical solution which has been pursued to include second-order terms O(ε^2). The lowest-order O(ε^0) model equations, known as the shallow-ice approximation (SIA), are asymptotically valid in the entire ice sheet domain except a small marginal zone provided the topographic variations are shallow, ie, possess wave height to wavelength ratios that are O(ε^1) and the constitutive relation for the stress deviator exhibits finite viscosity at zero effective shear stress (square root of second stress deviator invariant). We critically review earlier procedures and put them into the proper perspectives with regard to the original expansion procedures. We extend the zeroth-order theory to first and second order but present only those equations and deductions from them which lead to improved physical insight. In particular we derive stress formulas which show how the stresses depend on i) depth and surface slope, ii) surface topography and iii) stress deviator components, more complete than, and going beyond, known formulas of the literature. Finally we discuss numerically computed second-order stresses for the present state of the Greenland ice sheet. It turns out that they are typically three orders of magnitude smaller than the corresponding zeroth-order quantities, and that they are mainly determined by contributions due to zeroth-order stress deviators, rather than by topography effects. Their relative importance is largest close to the ice surface for the second-order pressure, and in the vicinity of ice domes for the horizontal, bed-parallel shear stresses. There are 229 references. - Ralf GreveClimatic Change 46 3 289 - 303 2000年08月 [査読有り][招待有り]
Numerical computations are performed with the three-dimensional polythermal ice-sheet model SICOPOLIS in order to investigate the possible impact of a greenhouse-gas-induced climate change on the Greenland ice sheet. The assumed increase of the mean annual air temperature above the ice covers a range from ΔT = 1℃ to 12℃, and several parameterizations for the snowfall and the surface melting are considered. The simulated shrinking of the ice sheet is a smooth function of the temperature rise, indications for the existence of critical thresholds of the climate input are not found. Within 1000 model years, the ice volume decrease is limited to 10% of the present volume for ΔT ≤ 3℃, whereas the most extreme scenario, ΔT = 12℃, leads to an almost entire disintegration, which corresponds to a sea-level equivalent of 7 m. The different snowfall and melting parameterizations yield an uncertainty range of up to 20% of the present ice volume after 1000 model years. - Ralf GreveIcarus 144 2 419 - 431 2000年04月 [査読有り][通常論文]
The perennial north polar H2O ice cap of Mars is investigated with the dynamic/thermodynamic ice-sheet model SICOPOLIS. Computational results for flow velocities, ice temperatures, and surface accumulation/ablation rates are presented for the steady state with present conditions as well as for transient scenarios over idealized obliquity cycles with periods of 1.3 Myr and 125 kyr. The transient simulations lead to a stop-and-go-type dynamics with a cold and almost stagnant modern ice cap and a warmer flowing ice cap for past large-obliquity periods. The most likely scenario for the present ice cap comprises an ice volume of 1.2 million km^3, a maximum thickness of 3 km, the absence of pronounced local isostasy, H2O-ice accumulation rates of the order of tenth-mm water equivalent (w.e.) per Earth year (yr), flow velocities of the order of mm/yr and an ice base far below pressure melting. - Alexey Savvin, Ralf Greve, Reinhard Calov, Bernd Mügge, Kolumban HutterAnnals of Glaciology 30 69 - 75 2000年 [査読有り][通常論文]
The modern dynamic and thermodynamic state of the entire Antarctic ice sheet is computed for a 242200 year paleoclimatic simulation with the three-dimensional polythermal ice-sheet model SICOPOLIS. The simulation is driven by a climate history derived from the Vostok ice core and the SPECMAP sea-level record. In a 872 km x 436 km region in western Dronning Maud Land (DML), where a deep ice core is planned for EPICA, new high-resolution ice-thickness data are used to compute an improved bedrock topography and a locally refined numerical grid is applied which extends earlier work (Calov and others, 1998). The computed fields of basal temperature, age and shear deformation, together with the measured accumulation rates, give valuable information for the selection of a drill site suitable for obtaining a high-resolution climate record for the last glacial cycle. Based on these results, a possible drill site at 73°59'S, 00°00'E is discussed, for which the computed depth profiles of temperature, age, velocity and shear deformation are presented. The geographic origin of the ice column at this position extends 320 km upstream and therefore does not leave the DML region. - A. J. Payne, P. Huybrechts, A. Abe-Ouchi, R. Calov, J. L. Fastook, R. Greve, S. J. Marshall, I. Marsiat, C. Ritz, L. Tarasov, M. P. A. ThomassenJournal of Glaciology 46 153 227 - 238 2000年 [査読有り][通常論文]
This paper discusses results from the second phase of the European Ice Sheet Modelling Initiative (EISMINT). It reports the intercomparison of ten operational ice-sheet models and uses a series of experiments to examine the implications of thermomechanical coupling for model behaviour. A schematic, circular ice sheet is used in the work which investigates both steady states and the response to stepped changes in climate. The major finding is that the radial symmetry implied in the experimental design can, under certain circumstances, break down with the formation of distinct, regularly spaced spokes of cold ice which extended from the interior of the ice sheet outward to the surrounding zone of basal melt. These features also manifest themselves in the thickness and velocity distributions predicted by the models. They appear to be a common feature to all of the models which took part in the intercomparison, and may stem from interactions between ice temperature, flow and surface form. The exact nature of these features varies between models, and their existence appears to be controlled by the overall thermal regime of the ice sheet. A second result is that there is considerable agreement between the models in their predictions of global-scale response to imposed climate change. - Magnus Weis, Ralf Greve, Kolumban HutterContinuum Mechanics and Thermodynamics 11 1 15 - 50 1999年02月 [査読有り][通常論文]
Ice shelves consist of two layers, an upper layer of meteoric ice nourished by the flow from the connected inland ice and precipitation, and a lower layer of marine ice that is built by the melting and freezing processes at the ice-ocean interface and the accretion of frazil ice from the underlying ocean. The governing thermomechanical equations in the two layers are formulated as are the boundary and transition conditions that apply at the free surface, the material interface between the meteoric and the marine ice and the ice-ocean interface. The equations comprise in the bulk mass balances for the ice and the salt water (in marine ice), momentum balance and energy balance equations, and at the boundaries kinematic equations as well as jump conditions of mass, momentum and energy. The side boundary conditions involve a prescription of the mass flow along the grounding line from the inland ice and a kinematic law describing the mass loss by calving along the floating ice-shelf front. An appropriate scaling, in which the shallowness of the ice shelves is used, gives rise to the development of a perturbation scheme for the solution of the three-dimensional equations, Its lowest-order approximation - the shallow-shelf approximation (SSA) - shows the ice flow to be predominantly horizontal with a velocity field independent of depth, but strongly depth-dependent temperature and stress distributions. This zeroth order shallow-shelf approximation excludes the treatment of ice rumples, ice rises and the vicinity of the grounding line, but higher-order equations may to within second-order accuracy in the perturbation parameter accommodate for these more complicated effects. The scaling introduced finally leads to a vertical integrated system of non-linear partial integrodifferential equations describing the ice flow and evolution equation for temperature and the free surfaces. - Ralf Greve, Karl-Heinz Wyrwoll, Anton EisenhauerAnnals of Glaciology 28 1 - 8 1999年 [査読有り][通常論文]
High resolution (TIMS) U-series dating of sea-level events obtained from coral-reef complexes suggests that global deglaciation from the Saale (penultimate) glacial to the Eem Interglacial (marine δ18O stages 6/5) may have occurred earlier in relation to Milankovitch insolation forcing than that from the Wisconsinan glacial to the Holocene Interglacial (marine δ18O stages 2/1). However, the interpretation of these data has been problematic because of the possibility of isotope exchange. In order to investigate whether these different lead-lag relations between Milankovitch forcing and ice volume are feasible from the point of view of large-scale ice-sheet dynamics and thermodynamics, the three-dimensional polythermal ice-sheet model SICOPOLIS (Simulation Code for Polythermal Ice Sheets) is applied to the entire Northern Hemisphere (which gives the major contribution to global ice-volume changes due to the relative stability of the Antarctic ice sheet) and simulations through the last two climatic cycles are conducted. The simulations cover the interval from 250 kyr sp until today and are driven by surface-temperature reconstructions of deep ice cores (GRIP, Vostok) and simple parameterizations for the change of precipitation with time. Discussion of the results is focused on the Saale/Eem and the Wisconsinan/Holocene transitions. The amount and rate of deglaciation are in good agreement with the SPECMAP record for both cases, and the evidence of the data for an early start of the Eem Interglacial is supported. - Ralf Greve, Magnus Weis, Kolumban HutterPaleoclimates: Data and Modelling 2 2-3 133 - 161 1998年 [査読有り][通常論文]
Using the three-dimensional numerical model SICOPOLIS for polythermal land-based ice sheets in the shallow ice approximation, simulations are performed to determine the velocity, temperature and water-content distributions as well as the evolution of the free surface, the cold-temperate-transition surface (CTS) and the basal surface within the Greenland Ice Sheet through time for a climate driving as determined by the (smoothed) GRIP palaeotemperature record. The model is driven by the temperature at the free surface, the global sea level and the geothermal heat flow 5 km below the basal surface. It uses plausible parameterizations for the accumulation and ablation rates, the basal sliding law and the constitutive behaviour (power-law rheology), in which the fluidity difference between glacial and interglacial ice is accounted for by appropriate enhancement factors. Computations that cover 250,000 years of climate history are performed with various sets of parameters to find optimal present conditions when compared with available data. To this end a misfit index is defined, and parameterizations are chosen so as to minimize it. It is shown that dating the ice at depth is crucially dependent on the “flux of age” into the base. However, other parameterizations such as the geothermal heat flow or the basal drag in the sliding law etc. equally influence the present geometry of the ice sheet. We investigate the results of the best-fit simulation with particular attention to the vicinity of Summit, the highest point of the Greenland Ice Sheet at 72°34'N, 37°38'W, in whose vicinity the two deep ice cores GRIP and GISP2 were drilled. For these boreholes, time series for the ice thickness and the basal temperature, present temperature-depth profiles and present age-depth profiles are presented. Furthermore, the ice-surface topography and the ice thickness in the vicinity of Summit is shown, and a comparison with high-resolution RES data is performed. - Reinhard Calov, Alexey Savvin, Ralf Greve, Imke Hansen, Kolumban HutterAnnals of Glaciology 27 201 - 206 1998年 [査読有り][通常論文]
The three-dimensional polythermal ice-sheet model SICOPOLIS is applied to the entire Antarctic ice sheet in support of the European Project for Ice Coring in Antarctica (EPICA). In this study, we focus on the deep ice core to be drilled in Dronning Maud Land (Atlantic sector of East Antarctica) as part of EPICA. It has not yet been decided where the exact drill-site will be situated. Our objective is to support EPICA during its planning phase as well as during the actual drilling process. We discuss a transient simulation with a climate forcing derived from the Vostok ice core and the SPECMAP sea-level record. This simulation shows the range of accumulation, basal temperature, age and shear deformation to be expected in the region of Dronning Maud Land. Based on these results, a possible coring position is proposed, and the distribution of temperature, age, horizontal velocity and shear deformation is shown for this column. - Ralf GreveJournal of Climate 10 5 901 - 918 1997年05月 [査読有り][通常論文]
Steady-state and transient climate-change computations are performed with the author's three-dimensional polythermal ice sheet model "Simulation Code for Polythermal Ice Sheets" for the Greenland Ice Sheet. The distinctive feature of this model is the detailed consideration of the basal temperate ice layer, in which the water content and its impact on the ice viscosity are computed; its transition surface to the cold ice region is accounted for by continuum-mechanical jump conditions on this interface. The simulations presented include steady states subject to a range of physical parameters and two different climates (present and glacial conditions), as well as three types of transient scenarios, namely (i) sinusoidal Milankovic-period forcing, (ii) paleoclimatic forcing from the Greenland Ice Core Project core reconstruction, and (iii) future greenhouse warming forcing. - Ralf GrevePhilosophical Transactions of the Royal Society A 355 1726 921 - 974 1997年05月 [査読有り][通常論文]
This paper is concerned with a new theoretical approach to model grounded ice sheets in three dimensions. These are considered as polythermal, i.e., there will be regions with temperatures below the pressure melting point ("cold ice") and regions with temperatures exactly at the pressure melting point ("temperate ice"). In the latter, small quantities of water may occur. Based on previous approaches, an improved theory of polythermal ice sheets is developed, which is founded on continuum-thermodynamic balance relations and jump conditions for mass, momentum and energy. The rheological behaviour is assumed to be that of an incompressible, nonlinear viscous and heat conducting fluid; because of the dependence of viscosity on temperature and on water content, the problem is thermo-mechanically coupled. After presenting analytic solutions for a simple geometry (ice sheet of uniform depth), the theory is subjected to a scaling procedure with the assumptions of a small aspect ratio (ratio between typical vertical dimension and typical horizontal dimension) and a small Froude number. This leads to the introduction of the polythermal shallow-ice approximation (SIA) equations. Finally, as an application of the model to a real problem, a numerically computed steady-state solution for the Greenland Ice Sheet under present climate conditions is presented and compared with the real ice sheet. - Ralf GreveJournal of Glaciology 43 144 307 - 310 1997年 [査読有り][通常論文]
The three-dimensional ice-sheet model SICOPOLIS is used to simulate the dynamic/thermodynamic behaviour of the entire Greenland ice sheet from 250 000 a BP until today. External forcing consists of a surface-temperature history constructed from δ18O data of the GRIP core, a snowfall history coupled linearly to that of the surface temperature, a piecewise linear sea-level scenario and a constant geothermal heat flux. The simulated Greenland ice sheet is investigated in the vicinity of Summit, the position where the maximum elevation is taken, and where the two drill sites GRIP and GISP2 are situated 28 km apart from each other. In this region, the agreement between modelled and observed topography and ice temperature turns out to be very good. Computed age-depth profiles for GRIP and GISP2 are presented, which can be used to complete the dating of these cores in the deeper regions where annual-layer counting is not possible. However, artificial diffusion influences the computed ages in a near-basal boundary layer of approximately 15% of the ice thickness, so that the age at the bottom of the cores cannot be predicted yet. - Frank G. M. van Tatenhove, Adeline Fabré, Ralf Greve, Philippe HuybrechtsAnnals of Glaciology 23 52 - 58 1996年 [査読有り][通常論文]
Ice-sheet modelling is an essential tool for estimating the effect of climate change on the Greenland ice sheet. The large spatial and long-term temporal scales of the ice-sheet model limits the amount of data which can be used to test model results. The geological record is useful because it provides test material on the time-scales typical for the memory of ice sheets (millennia). This paper compares modelled ice-margin positions with a geological scenario of ice-margin positions since the Last Glacial Maximum to the present in West Greenland. Morphological evidence of ice-margin positions is provided by moraines. Moraine systems are dated by 14C-dated marine shells and terrestrial peat. Three Greenland ice-sheet models are compared. There are distinct differences in modelled ice-margin positions between the models and between model results and the geological record. Disagreement between models and the geological record in the near-coastal area is explained by the inadequate treatment of marginal processes in a tide-water environment. A smaller than present ice sheet around the warm period in the Holocene (Holocene climatic optimum) only occurs if such a period appears in the forcing (ice-core record) or used temporal resolution. Smoothing of the GRIP record with a 2000 year average eliminates the climatic signal related to the Holocene climatic optimum. This underlines the importance of short-term and medium-term variations (decades, centuries) in climatic variables in determining ice-margin positions in the past but also in the future. - Philippe Huybrechts, Anthony J. Payne, EISMINT Intercomparison Group (including Ralf Greve)Annals of Glaciology 23 1 - 12 1996年 [査読有り][通常論文]
We present a series of benchmark experiments designed for testing and comparing numerical ice-sheet models. Following the outcome of two EISMINT workshops organized to intercompare large-scale ice-sheet models currently in operation, model benchmark experiments ate described for ice sheets under fixed and moving margin conditions. These address both steady-state and time-dependent behaviour under schematic boundary conditions and with prescribed physics. A comparison was made of each model’s prediction of basic geophysical variables such as ice thickness, velocity and temperature. Consensus achieved in the model inter-comparison provides reference solutions against which the accuracy and consistency of ice-sheet modelling codes can be assessed. - Imke Hansen, Ralf GreveAnnals of Glaciology 23 382 - 387 1996年 [査読有り][通常論文]
An approach to simulate the present Antarctic ice sheet with reaped to its thermomechanical behaviour and the resulting features is made with the three-dimensional polythermal ice-sheet model designed by Greve and Hutter. It treats zones of cold and temperate ice as different materials with their own properties and dynamics. This is important because an underlying layer of temperate ice can influence the ice sheet as a whole, e.g. the cold ice may slide upon the less viscous binary ice water mixture. Measurements indicate that the geothermal heat flux below the Antarctic ice sheet appears to be remarkably higher than the standard value of 42 mW/m2 that is usually applied for Precambrian shields in ice-sheet modelling. Since the extent of temperate ice at the base is highly dependent on this heat input from the lithosphere, an adequate choice is crucial for realistic simulations. We shall present a series of steady-state results with varied geothermal heat flux and demonstrate that the real ice-sheet topography can be reproduced fairly well with a value in the range 50–60 mW/m2. Thus, the physical parameters of ice (especially the enhancement factor in Glen’s flow law) as used by Greve (1995) for polythermal Greenland ice-sheet simulations can be adopted without any change. The remaining disagreements may he explained by the neglected influence of the ice shelves, the rather coarse horizontal resolution (100 km), the steady-state assumption and possible shortcomings in the parameterization of the surface mass balance. - Ralf Greve, Douglas R. MacAyealAnnals of Glaciology 23 328 - 335 1996年 [査読有り][通常論文]
A crucial element of several leading theories of Laurentide ice-sheet instability (i.e. Heinrich events and advance/retreat cycles of the southern margin) is the evolution of melting conditions at the subglacial bed. Despite the great importance basal-temperature conditions play in these theories, relatively little has been done to test their physical plausibility. We therefore undertake a numerical model study of the ice-sheet temperature field along an important transect which extends from the lobate southern margin of the Laurentide ice sheet to the iceberg-calving from at the terminus of Hudson Strait. Our experiments illustrate the influence of important aspects of ice-sheet thermodynamics on ice-sheet instability, including horizontal advection and the development of an internal temperate-ice reservoir. Free oscillations of the basal temperature and ice thickness in Hudson Strait are possible under a restricted range of parameters elucidated by the model. These free oscillations may provide a basis for understanding ice-sheet instability, e.g. Heinrich events, with time-scales in the range of 10^3–10^4 a. - Application of a polythermal ice sheet model to the Antarctic ice sheet: Steady-state solution and response to Milankovic cyclesImke Hansen, Ralf Greve, Kolumban HutterProceedings of the 5th International Symposium on Thermal Engineering and Sciences for Cold Regions (ed. Y. Lee and W. Hallett) 89 - 96 1996年 [査読無し][通常論文]
- Ralf Greve, Kolumban HutterAnnals of Glaciology 21 8 - 12 1995年 [査読有り][通常論文]
Computations over 50000 years into steady state with Greve’s polythermal ice-sheet model and its numerical code are performed for the Greenland ice sheet with today’s climatological input (surface temperature and accumulation function) and three values of the geothermal heat flux: (42, 54.6, 29.4) mW/m2. It is shown that through the thermomechanical coupling the geometry as well as the thermal regime, in particular that close to the bed, respond surprisingly strongly to the basal thermal heat input. The most sensitive variable is the basal temperature field, but the maximum height of the summit also varies by more than ±100 m. Furthermore, some intercomparison of the model outputs with the real ice sheet is carried out, showing that the model provides reasonable results for the ice-sheet geometry as well as for the englacial temperatures. - Thilo Koch, Ralf Greve, Kolumban HutterProceedings of the Royal Society A 445 1924 415 - 435 1994年05月 [査読有り][通常論文]
In this paper the agreement between laboratory experiments performed with three-dimensional granular avalanches moving along a partly curved surface and their numerical predictions shall be examined. First, the most important elements of the theory describing the flow of a cohesionless granular material down a rough bed are presented. Based on the depth-averaged model equations, an advanced numerical integration scheme is developped by making use of a Lagrangian representation (i. e., the grid moves with the deforming pile) and a finite difference approximation that handles the numerically two-dimensional problem accurately. Second, experiments are described that were conducted with a finite mass of granular material moving down, respectively, an inclined plane and a surface consisting of an inclined and a horizontal plane connected by a curved transition area; the initial geometry of the avalanche is generated by a spherical cap. Third, for a number of different experiments a comparison is carried out between the experimentally determined positions of the granular avalanche during its motion and the numerical prediction of these positions. It shows that the numerical results fit the experimental data surprisingly well. - Ralf Greve, Thilo Koch, Kolumban HutterProceedings of the Royal Society A 445 1924 399 - 413 1994年05月 [査読有り][通常論文]
This paper deals with three-dimensional gravity driven free surface flows of piles of granular materials along bottom profiles that are weakly curved downward and plane laterally. We present in detail a three-dimensional extension of the two-dimensional Savage-Hutter model for such granular avalanches. In this extended model, the avalanche is described as a three-dimensional incompressible continuum obeying a Coulomb dry friction law at the base and a Mohr Coulomb plastic yield criterion in the interior. Based on this, the balance laws of mass and linear momentum and kinematic and stress boundary conditions at the free surface and the base are used to derive depth-averaged dynamic equations that describe the temporal evolution of the height and the depth-averaged horizontal velocity components as functions of position and time. A computation is performed for a pile of granular material with an initial spherical cap geometry moving down an inclined plane. - Ralf Greve, Kolumban HutterPhilosophical Transactions of the Royal Society A 342 1666 573 - 600 1993年03月 [査読有り][通常論文]
This paper deals with the theoretical-numerical and experimental treatment of two dimensional avalanches of cohesionless granular materials moving down a confined curved chute. Depth-averaged field equations of balance of mass and linear momentum as prescribed by Savage & Hutter (1991) are used. They describe the temporal evolution of the depth averaged streamwise velocity and the distribution of the avalanche depth and involve two phenomenological parameters, the internal angle of friction, ϕ,and the bed friction angle, δ, both as constitutive properties of Coulomb-type behaviour. The equations incorporate weak to moderate curvature effects of the bed. Experiments were carried out with different granular materials in a chute with partly convex and partly concave curved geometry. In these experiments the motion of the granular avalanche is followed from the moment of release to its standstill by using high speed photography, whence recording the geometry of the avalanche as a function of position and time. Two different bed linings, drawing paper and no. 120 SIA sandpaper, were used to vary the bed friction angle, δ. Both, the internal angle of friction, ϕ, and the bed friction angle, δ, were measured, and their values used in the theoretical model. Because of the bump and depending upon the granulate-bed combination an initial single pile of granular avalanche could evolve as a single pile throughout its motion and be deposited above or below the bump in the bed; or it could separate in the course of the motion into two piles which are separately deposited above and below the bump. Comparison of the experimental findings with the computational results proved to lead to good to excellent correspondence between experiment and theory. Even the development of the detailed geometry of the granular avalanche is excellently reproduced by the model equations, if δ < ϕ. Occasional deviations may occur; however, they can in all cases be explained by onsetting instabilities of the numerical scheme or by experimental artefacts that only arise when single particles have shapes prone to rolling. - Kolumban Hutter, Ralf GreveJournal of Glaciology 39 132 357 - 372 1993年 [査読有り][通常論文]
This paper is concerned with the motion of an unconfined finite mass of granular material down an inclined plane when released from a rest position in the shape of a circular or elliptical paraboloid. The granular mass is treated as a frictional Coulomb-like continuum with a constant angle of internal friction. The basal friction force is assumed to be composed of a Coulomb-type component with a bed-friction angle that is position-dependent and a viscous Voellmy-type resistive stress that is proportional to the velocity squared. The model equations are those of Hutter and others (in press b) and form a spatially two-dimensional set for the evolution of the avalanche height and the depth-averaged in-plane velocity components; they hold for a motion of a granular mass along a plane surface. Similarity solutions, i.e. solutions which preserve the shape and the structure of the velocity field, are constructed by decomposing the motion into that of the centre of mass and the deformation relative to it. This decomposition is possible provided the effect of the Voellmy drag on the deformation is ignored. With it, the depth and velocities relative to those of the centre of mass of the moving pile Can be determined analytically. It is shown that the pile has a parabolic cap shape and contour lines are elliptical. The semi-axes and the position and velocity of the centre of mass are calculated numerically. We explicitly show that (i) For two-dimensional spreading, a rigid-body motion does not exist, no matter what be the values of the bed-friction angle and the coefficient of viscous drag. (ii) A steady final velocity of the centre of the mass cannot be assumed, but the motion of the centre of mass depends strongly on the value of the Voellmy coefficient. (iii) The geometry of the moving pile depends on the variation of the bed-friction angle with position, as well as on the value of the coefficient of viscous drag.
書籍
- Expedition Erde. Wissenswertes und Spannendes aus den Geowissenschaften (4th Edition)Martin Claussen, Ralf Greve, Ulrich Cubasch (担当:分担執筆範囲:Was ist eigentlich Klima? Klima und Klimaänderungen)
MARUM Bibliothek 2015年07月 (ISBN: 9783000490453) 352-359 - J. A. Church, P. U. Clark, A. Cazenave, J. M. Gregory, S. Jevrejeva, A. Levermann, M. A. Merrifield, G. A. Milne, R. S. Nerem, P. D. Nunn, A. J. Payne, W. T. Pfeffer, D. Stammer, A. S. Unnikrishnan, 57 contributing authors including R. Greve (担当:分担執筆範囲:Sea level change)
Cambridge University Press 2013年09月 1137-1216 - Expedition Erde. Wissenswertes und Spannendes aus den Geowissenschaften (3rd Edition)Martin Claussen, Ralf Greve, Ulrich Cubasch (担当:分担執筆範囲:Was ist eigentlich Klima? Klima und Klimaänderungen)
MARUM Bibliothek 2010年10月 (ISBN: 9783000307720) 326-333 - Continuum Mechanics, Fluids, HeatSwantje Bargmann, Hakime Seddik, Ralf Greve (担当:分担執筆範囲:On a thermodynamically consistent flow model for induced anisotropy in polar ice)
WSEAS Press 2010年02月 (ISBN: 9789604741588) 114-119 - Dynamics of Ice Sheets and GlaciersRalf Greve, Heinz Blatter (担当:共著)
Springer 2009年08月 (ISBN: 9783642034145) 287 pp. - 地球温暖化の科学グレーベ ラルフ (担当:分担執筆範囲:地球温暖化と陸域雪氷の役割、および海水準上昇)
北海道大学出版会 2007年 (ISBN: 9784832981812) 105-112 - Kontinuumsmechanik. Ein Grundkurs für Ingenieure und PhysikerRalf Greve (担当:単著)
Springer 2003年 (ISBN: 3540007601) 302 pp. - Continuum Mechanics and Applications in Geophysics and the EnvironmentRalf Greve (担当:分担執筆範囲:Glacial isostasy: Models for the response of the Earth to varying ice loads)
Springer 2001年 (ISBN: 3540416609) 307-325 - Continuum Mechanics and Applications in Geophysics and the EnvironmentBrian Straughan, Ralf Greve, Harald Ehrentraut, Yongqi Wang (担当:共編者(共編著者))
Springer 2001年 (ISBN: 3540416609) 393 pp. - Advances in Cold-Region Thermal Engineering and SciencesBernd Mügge, Alexey A. Savvin, Reinhard Calov, Ralf Greve (担当:分担執筆範囲:Numerical age computation of the Antarctic ice sheet for dating deep ice cores)
Springer 1999年 (ISBN: 3540663339) 307-318 - Advances in Cold-Region Thermal Engineering and SciencesRalf Greve, Bernd Mügge, Dambaru R. Baral, Olaf Albrecht, Alexey A. Savvin (担当:分担執筆範囲:Nested high-resolution modelling of the Greenland Summit region)
Springer 1999年 (ISBN: 3540663339) 285-306
講演・口頭発表等
- 氷床数値モデル開発と氷床変動に関する研究 [招待講演]グレーべ ラルフ日本雪氷学会・雪氷研究大会 2022年10月 口頭発表（招待・特別）
- History and Japanese contribution to the International Association of Cryospheric Sciences IACS [招待講演]Ralf Greve日本地球惑星科学連合2019年大会 2019年05月 口頭発表（招待・特別）
- Ralf Greve千歳光科学国際フォーラム 2017年10月 口頭発表（招待・特別） 千歳科学技術大学
- Ice sheet modelling and applications to Greenland, Antarctica and the Martian polar caps [招待講演]Ralf GreveAustralasian Fluid Mechanics Conference 2012年12月 口頭発表（基調）
- Ice sheet modelling and applications to the past, present and future glaciation of the Earth [招待講演]Ralf GreveIPICS (International Partnerships in Ice Core Sciences) Open Science Conference 2012年10月 口頭発表（基調）
- Glaciation of Mars from 10 million years ago until 10 million years into the future simulated with the model MAIC-2 [招待講演]Ralf Greve, Björn Grieger, Oliver J. Stenzel日本地球惑星科学連合2012年大会 2012年05月 口頭発表（招待・特別）
- Cooperation between the Nordic countries and Japan in advanced ice sheet and glacier modelling [招待講演]Ralf Greve, Thomas ZwingerNorthern Environmental Research Symposium, Hokkaido University Sustainability Weeks 2011年10月 口頭発表（招待・特別）
- Do the Martian Polar Layered Deposits flow, now or in the past? [招待講演]D. Fisher, W. Durham, R. Greve, J. Holt, C. Hvidberg, S. MilkovichFifth International Conference on Mars Polar Science and Exploration 2011年09月 シンポジウム・ワークショップパネル（指名）
- SeaRISE: Modelling the present-day state and future evolution of the Greenland Ice Sheet with the models SICOPOLIS and IcIES [招待講演]Ralf Greve, Fuyuki Saito, Ayako Abe-OuchiAGU (American Geophysical Union) Fall Meeting 2010年12月 口頭発表（招待・特別）
- Implementation of ice shelf dynamics and marine ice dynamics in the ice sheet model SICOPOLIS [招待講演]Ralf Greve, Tatsuru Sato, Thorben DunseInternational Glaciological Conference "Ice and Climate Change: A View from the South" 2010年02月 口頭発表（招待・特別）
- Dynamic/thermodynamic modelling of the Antarctic Ice Sheet with the focus on the vicinity of Dome Fuji [招待講演]Ralf Greve, Hakime Seddik, Thomas Zwinger, Luca Placidi2nd International Symposium on the Dome Fuji Ice Core and Related Topics 2009年11月 口頭発表（招待・特別）
- Dynamic/thermodynamic modelling of ice sheets in changing climates [招待講演]Ralf GreveInternational Symposium "Frontiers of Low Temperature Science", Hokkaido University Sustainability Weeks 2009年11月 口頭発表（招待・特別）
- Decay of the Greenland Ice Sheet due to surface-meltwater-induced acceleration of basal sliding [招待講演]Ralf GreveNuuk Climate Days: Changes of the Greenland Cryosphere Workshop & International Symposium on the Arctic Freshwater Budget 2009年08月 口頭発表（招待・特別）
- Increased future sea level rise due to rapid decay of the Greenland Ice Sheet? [招待講演]Ralf GreveIAMAS-IAPSO-IACS Joint Assembly (MOCA-09) 2009年07月 口頭発表（招待・特別）
- Rapid decay of the Greenland and Antarctic ice sheets? [招待講演]Ralf GreveSentinel Earth, Detection of Environmental Change 2008年07月 口頭発表（招待・特別）
- Dynamic/thermodynamic modeling of the Gorshkov crater glacier at Ushkovsky volcano, Kamchatka [招待講演]Ralf Greve, Thomas Zwinger, Olivier Gagliardini, Evgeny Isenko, Erik Edelmann, Hakime SeddikAGU (American Geophysical Union) Fall Meeting 2007年12月 口頭発表（招待・特別）
- Simulation of the north and south polar caps of Mars over climate cycles [招待講演]Ralf GreveAOGS (Asia Oceania Geosciences Society) 2nd Annual Meeting 2005年06月 口頭発表（招待・特別）
- Evolution and dynamics of the Greenland ice sheet over past glacial-interglacial cycles and in future climate-warming scenarios [招待講演]Ralf Greve5th International Conference on Global Change: Connection to the Arctic (GCCA-5) 2004年11月 口頭発表（招待・特別）
作品等
- Ralf Greve, SICOPOLIS Authors 1992年03月 - 現在 SICOPOLIS (SImulation COde for POLythermal Ice Sheets, www.sicopolis.net) is a 3D model that simulates the evolution, dynamics and thermodynamics of large ice sheets and ice caps.
- Ralf Greve, Björn Grieger, Oliver J. Stenzel 2007年10月 -2013年02月 The Mars Atmosphere-Ice Coupler MAIC-2 is a simple, latitudinal model that consists of a set of parameterizations for the surface temperature, the atmospheric water transport and the surface mass balance (condensation minus evaporation) of water ice. It is driven directly by the orbital parameters obliquity, eccentricity and solar longitude of perihelion.
その他活動・業績
- Ralf Greve 低温研ニュース 53 12 -14 2022年07月 [査読無し][招待有り]
- Ralf Greve, Christopher Chambers, Reinhard Calov Zenodo 3971251 2020年09月 [査読無し][通常論文]
The Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6) brings together a consortium of international ice-sheet and climate modellers to simulate the contribution from the Greenland and Antarctic ice sheets to future sea-level rise. In this document (supplementary to Goelzer et al. 2020, doi: 10.5194/tc-14-3071-2020), we describe the ISMIP6 Greenland Tier-1 and Tier-2 experiments carried out with the ice-sheet model SICOPOLIS. First, we conduct a paleoclimatic spin-up over the last glacial-interglacial cycle until the year 1990. In this spin-up, we employ a nudging technique for the topography and aim at optimizing the match between simulated and observed surface velocities by adjusting the amount of basal sliding for individual drainage systems. Then, we carry out a historical run to bridge the gap between 1990 and 2015. The future climate projections run from the beginning of 2015 until the end of 2100. The simulated mass loss by 2100 is 133.0 ± 40.7 mm SLE (mean ± 1-sigma uncertainty; SLE: sea-level equivalent) for the RCP8.5/SSP5-8.5 pathway that represents "business as usual", and it is 48.6 ± 6.2 mm SLE for the RCP2.6/SSP1-2.6 pathway that represents substantial emissions reductions. The large difference between the results for the two pathways highlights the importance of efficient climate change mitigation for limiting sea-level rise. Further, results obtained with forcings from the newer CMIP6 global climate models consistently produce larger mass losses than those obtained with the older CMIP5 global climate models. - Ralf Greve, Reinhard Calov, Takashi Obase, Fuyuki Saito, Shun Tsutaki, Ayako Abe-Ouchi Zenodo 3971232 2020年09月 [査読無し][通常論文]
The Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6) brings together a consortium of international ice-sheet and climate modellers to simulate the contribution from the Greenland and Antarctic ice sheets to future sea-level rise. In this document (supplementary to Seroussi et al. 2020, doi: 10.5194/tc-14-3033-2020), we describe the ISMIP6 Antarctica Tier-1 and Tier-2 experiments carried out with the ice-sheet model SICOPOLIS. First, we conduct a paleoclimatic spin-up over the last glacial-interglacial cycle until the year 1990. In this spin-up, we employ a nudging technique for the topography and aim at optimizing the match between simulated and observed surface velocities by adjusting the amount of basal sliding for individual drainage systems. Then, we carry out a historical run to bridge the gap between 1990 and 2015. The future climate projections run from the beginning of 2015 until the end of 2100. Results reveal a non-uniform response of the Antarctic ice sheet: for both employed future climate scenarios (RCP8.5/SSP5-8.5, RCP2.6/SSP1-2.6), mass losses and gains occur, depending on the specific forcing (provided by CMIP5 and CMIP6 global climate models). This is due to the counteracting effects of increasing ocean temperature (leading to a loss) and increasing precipitation (leading to a gain). For RCP8.5/SSP5-8.5, the ensemble mean is a mass loss of 18.5 mm SLE (sea-level equivalent) by 2100, and for RCP2.6/SSP1-2.6 it is 8.4 mm SLE. However, the uncertainty range is quite large, including the possibility of a mass loss of more than 100 mm SLE under RCP8.5/SSP5-8.5. - Ralf Greve Proceedings of the 18th Chitose International Forum on Photonics Science & Technology 12 -17 2018年07月 [査読無し][招待有り]
- Ralf Greve 低温研ニュース 45 8 -9 2018年06月 [査読無し][招待有り]
- Ian B. Smith, Eric Larour, Nathan E. Putzig, Ralf Greve, Nicole-Jeanne Schlegel Sixth International Conference on Mars Polar Science and Exploration. LPI Contribution No. 1926 6072 2016年09月 [査読無し][通常論文]
- Igor V. Polyakov, Robert Bolton, Ralf Greve, Jenny Hutchings, Seong-Joong Kim, Yongwon Kim, Sang H. Lee, Tetsuo Ohata, Fuyuki Saito, Atsuko Sugimoto, Rikie Suzuki Polar Science 8 (2) 53 -56 2014年 [査読無し][通常論文]
Rapid and dramatic climate changes in the Arctic and the projection of their impacts on lower-latitude regions require careful evaluation, understanding, and use of multidisciplinary, internationally coordinated efforts. The Third International Symposium on Arctic Research (ISAR-3), devoted to these objectives, was held on January 14-17, 2013 in Tokyo, and was an essential step in this direction. The pool of papers that make up this Special Issue provides an insight into the discussions conducted during the ISAR-3 meeting. - 横川美和, 泉典洋, 内藤健介, 山田朋人, GREVE Ralf 土木学会論文集 B1(水工学) 69 (4) I.1129 -I.1134 2013年 [査読無し][通常論文]
The spiral troughs observed on the surface of Mars' north polar ice cap show upstream-migrating structures, which indicate that those may possibly be cyclic steps formed by a density current created by cooling of the atmosphere due to the ice. It can be useful to estimate the formative process of the Mars' polar ice cap and thus the climatic history of Mars using the analogues of cyclic steps on the Earth. In this study, we have performed a series of physical experiments aimed at the formation of cyclic steps on ice by flowing fluid. Temperature distribution plays a quite important role for the formation and development of step topography on the ice surface, and was set as ice < fluid < ambient air in this experiment. As a result, step topography was formed on the ice except the case whose Fr is lowest, i.e., 0.76, and the steps generally developed upstream direction. The results of the present experiment agree with the mathematical model describing the evolution of the ice surface by flowing fluid. - 過去と将来の気候における火星の水氷堆積物の進化に関する数値シミュレーショングレーベ ラルフ 研究助成事業・研究成果報告書 59 -64 2012年07月 [査読無し][通常論文]
- J. W. Holt, R. Greve, I. B. Smith, L. E. Steel, T. C. Cowan 43rd Lunar and Planetary Science Conference. LPI Contribution No. 1659 2879 2012年03月 [査読無し][通常論文]
- Ralf Greve, Björn Grieger, Oliver J. Stenzel Fifth International Conference on Mars Polar Science and Exploration. LPI Contribution No. 1631 6004 2011年09月 [査読無し][通常論文]
- 過去と将来の気候における南極氷床の変動と力学的挙動に関する数値シミュレーショングレーベ ラルフ, 杉山 慎 研究助成事業・研究成果報告書 49 -53 2010年06月 [査読無し][通常論文]
- 気候変動に伴う火星の極氷床の進化と動力学グレーベ ラルフ 研究助成事業・研究成果報告書 37 -41 2008年05月 [査読無し][通常論文]
- Ralf Greve Bulletin of the American Meteorological Society 87 (12) 1759 -1760 2006年12月 [査読無し][招待有り]
- Ralf Greve Fourth International Conference on Mars Polar Science and Exploration. LPI Contribution No. 1323 8002 2006年 [査読無し][通常論文]
- Klimarekonstruktion aus dem Eis großer EisschildeKolumban Hutter, Ralf Greve, Reinhard Calov Thema Forschung (Darmstadt University of Technology, Germany) 2/2003 24 -32 2003年 [査読無し][招待有り]
- Kommt die Klimakatastrophe?Ralf Greve Der Gesundheitsberater (Organ der Gesellschaft für Gesundheitsberatung GGB e.V., Lahnstein, Germany) 2/02 8 -10 2002年 [査読無し][招待有り]
- Klima und KlimaänderungenMartin Claussen, Ralf Greve, Ulrich Cubasch Wissenschaftliche Mitteilungen aus dem Institut für Meteorologie der Universität Leipzig, Sonderheft zum Jahr der Geowissenschaften -- Atmosphäre 44 -50 2002年 [査読無し][招待有り]
- Ralf Greve, Volker Klemann, Detlef Wolf Second International Conference on Mars Polar Science and Exploration. LPI Contribution No. 1057 51 -52 2000年 [査読無し][通常論文]
- Ralf Greve First International Conference on Mars Polar Science and Exploration. LPI Contribution No. 953 13 -15 1998年 [査読無し][通常論文]
- Auswirkungen des Treibhauseffektes auf das grönländische EisschildRalf Greve VESGO Mitteilungen (Verein zur Erforschung und zum Schutz der Gewässer Ottendorf, Germany) 1/96 16 -17 1996年 [査読無し][通常論文]
- EGIG line simulations with a 2-d polythermal ice sheet modelRalf Greve Open File Series (Geological Survey of Greenland, Copenhagen, Denmark) 94/13 47 -49 1994年 [査読無し][通常論文]
- An improved polythermal ice sheet modelRalf Greve Open File Series (Geological Survey of Greenland, Copenhagen, Denmark) 93/5 22 -24 1993年 [査読無し][通常論文]
受賞
- 2023年04月 国際雪氷学会 Richardson Medal (2022)
受賞者: The ISMIP6 team (グレーブ・ラルフを含む80名以上) - 2022年10月 日本雪氷学会 学術賞
氷床数値モデル開発と氷床変動に関する研究受賞者: グレーベ ラルフ - 2015年03月 北海道大学 研究総長賞
奨励賞受賞者: グレーベ ラルフ
共同研究・競争的資金等の研究課題
- 北極域における沿岸環境の変化とその社会影響文部科学省：北極域研究加速プロジェクト（ArCS II）研究期間 : 2020年06月 -2025年03月代表者 : 杉山 慎, et al.
- 気象気候予測と予測手法の高度化文部科学省：北極域研究加速プロジェクト（ArCS II）研究期間 : 2020年06月 -2025年03月代表者 : 羽角 博康, et al.
- 日本学術振興会：科学研究費助成事業 新学術領域研究(研究領域提案型)研究期間 : 2017年06月 -2022年03月代表者 : 阿部 彩子, 吉森 正和, 草原 和弥, 齋藤 冬樹, 岡 顕, グレーベ ラルフ◆南極氷床モデリング：氷床モデルを南極用に設定し海洋ー氷床相互作用や底面過程を改良した。さらに将来予測実験ISMIP6の実行に向けた準備を行なった。棚氷底面融解を外力とする氷床の定常・非定常実験を実施。・気候モデルによる温暖化実験結果を入力に用いた実験や、長時間スケールの氷床変動再現実験を開始した。・南極変動に関わる古気候氷床実験を実施。モデルの不確定性の評価を行った。 ◆南極氷床の質量収支解析：・MIROCの降水量や気温や大気循環に関するデータによるモデル検証を行い。20世紀再現バイアスなどとの関係を調べた。 ◆南大洋モデリング：・氷期の数値実験に基づいて物理環境など各要素の再現性についての検討を進める。・底層水班と連携した南大洋における底層水形成や海氷分布などの検討を行った。生態系班と連携した南大洋での生物ポンプ過程の検討。氷床・気候班と連携した氷床コアによるCO2濃度データとモデル結果との直接の比較、氷期CO2低下の理解に向けた研究を進めた。過去及び将来における海洋酸性化に関する数値実験を実施した。氷期のCO2のモデリングについて論文執筆を進める一方、氷期から退氷期の実験の準備を進めた。 ◆長期気候-氷床モデリング：過去数百万年の気候と氷床の変化に関して大気海洋結合モデルMIROCの結果と南極氷床モデルを組み合わせた長期気候-氷床モデル実験を準備し、固体地球班との連携による古気候データとの比較検討によって、南極氷床と気候の変動メカニズムを調べた。
- 日本学術振興会：科学研究費助成事業 基盤研究(S)研究期間 : 2017年05月 -2022年03月代表者 : 阿部 彩子, 大河内 直彦, 吉森 正和, 齋藤 冬樹, 藤田 耕史, グレーベ ラルフ, 川村 賢二大気海洋結合モデルや氷床モデル、植生モデル、海洋物質循環モデル、同位体モデルに関して、過去150万年の氷床や気候、海洋のシミュレーションにとって必要な開発改良課題に取り組み、古気候指標と直接比較可能にするモデリング体制作りを開始した。 これまでに実施した北半球氷床の過去40万年の計算を過去80万年に拡張した。氷期から間氷期への移行の条件と考えられる地球軌道要素や二酸化炭素濃度を変化させ、氷床と気候の計算を実施することで、それぞれの役割の時代による違いを定量化する。更に、過去150万年のモデリングに着手し、約100万年前に氷期サイクルが4万年周期から10万年周期へ遷移した原因とメカニズムに迫る為の様々な感度実験を計画し、実験を開始した。 最終退氷期を含む複数の退氷期において連続的非定常の実験をMIROCを用いて行い、退氷期における氷床-海洋-大気の相互作用についての感度実験を実施した。その結果、北大西洋での風と海氷の相互作用が海洋深層循環と気候の維持に重要であることがわかった。また最終退氷期については、IcIES-MIROCを用いて北大西洋へ流入する氷床融解水のシナリオを調べ、MIROCに与える氷床融解水量を様々に変える実験を行った。氷床と海洋、気候の相互作用を分析することで、様々な問題を解明している途中である。 平均気候の決定条件である二酸化炭素濃度や軌道要素を変化させる感度実験を多数実施し、振動の発生や維持の条件を詳細に調べた。深層循環やグリーンランドの気温、中低緯度の降水量について振動の2つのモードを解析するとともに、海洋炭素循環モデルによって海水中の炭素同位体を計算し、データとの直接比較を行った。海洋深層循環の外的要因に対する応答の性質をその多重構造に着目して解き明かすため、様々な二酸化炭素濃度や軌道要素の条件下で、淡水流入を増減させる実験を実施した。
- Modelling the future mass loss of the Greenland ice sheet due to atmospheric and oceanic changes低温科学研究所：リーダーシップ研究助成研究期間 : 2020年04月 -2021年03月代表者 : グレーベ ラルフ, チェンバース クリストフアー, 阿部 彩子, 齋藤 冬樹, HUMBERT Angelika
- 日本学術振興会：科研費基盤研究（A)研究期間 : 2016年04月 -2020年03月代表者 : グレーベ ラルフ, 杉山 慎, 齋藤 冬樹, 榎本 浩之, 東 久美子
- グリーンランドにおける気候・氷床変動文部科学省：北極域研究推進プロジェクト（ArCS）研究期間 : 2015年10月 -2020年03月代表者 : 東 久美子, et al.
- グリーンランドにおける氷河氷床・海洋相互作用文部科学省：北極域研究推進プロジェクト（ArCS）研究期間 : 2015年10月 -2020年03月代表者 : 杉山 慎, et al.
- 日本学術振興会：科学研究費助成事業研究期間 : 2017年04月 -2018年03月代表者 : 阿部 彩子, 吉森 正和, 齋藤 冬樹, Greve Ralf, 川村 賢二本研究、基盤研究Ａ「急激な気候変動の大気中二酸化炭素濃度への依存度の解明」では、数千年周期で繰り返す急激な気候変動について、 大気海洋結合モデルを用いて再現し、大気中二酸化炭素濃度を変化させて気候と深層海洋循環の定常応答を調べる感度実験を行い、急激な気候変動が起こりやすい条件を明らかにしようとすること、 そして、氷期から間氷期への移行における大気・海洋・氷床の相互作用を複数のモデルの結合により再現し、過去150万年の氷期サイクルの卓越周期が4万年から10万年に移り変わった原因やプロセスを提示することを目指している。 Ｈ２９年の２ヶ月で、大気海洋結合モデル（ＭＩＲＯＣ）と氷床モデル、植生モデル、海洋炭素循環モデルを統合的に用いた数値実験に着手した。 また、大気海洋結合モデルを用いて再現し、大気中二酸化炭素濃度を変化させて気候と深層海洋循環の異なる応答を調べる感度実験を数多く実行している段階である。 今後の研究目標は、基盤研究Ｓ「過去の大規模な気候変動における氷床・海洋・気候の相互作用の解明」（代表阿部彩子）で達成していく予定である。
- 日本学術振興会：科学研究費助成事業 基盤研究(A)研究期間 : 2013年04月 -2016年03月代表者 : 阿部 彩子, グレーベ ラルフ, 川村 賢二, 吉森 正和, 齋藤 冬樹, 羽角 博康, 芳村 圭, 大河内 直彦, 岡 顕, 奥野 淳一10 万年周期で交代する氷期サイクルの究極的要因を調べる為に最新の氷床―気候モデルを用いたシミュレーションを行なった。その結果、氷期サイクルは日射変化に対して気候システムが応答し、大気－氷床－地殻の相互作用によりもたらされたものであると突き止めた。また、大気中の二酸化炭素は氷期サイクルに伴って変動し、その振幅を増幅させる働きがあるが、主体的に10 万年周期を生み出しているわけではないことも分かった。これらの結果は気候変動のの理解を深め、地球温暖化予測に用いられる氷床－気候モデルの信頼性を検証する上で重要な意義がある。また、より普遍的に過去の気候変動の原因を解き明かす道筋が出来た。
- グリーンランド氷床Qaanaaq 流域の近年および将来の変動に関するモデル開発と数値実験低温科学研究所：リーダーシップ研究助成研究期間 : 2014年04月 -2015年03月代表者 : グレーベ ラルフ, セディック ハキム, 阿部 彩子, 杉山 慎, 齋藤 冬樹, ZWINGER Thomas
- 日本学術振興会：科研費基盤研究（A)研究期間 : 2010年04月 -2014年03月代表者 : グレーベ ラルフ, 阿部 彩子, 杉山 慎, 藤田 秀二, 本山 秀明, 齋藤 冬樹
- 過去と将来の気候における火星の水氷堆積物の進化に関する数値シミュレーション低温科学研究所：リーダーシップ研究助成研究期間 : 2011年04月 -2012年03月代表者 : グレーベ ラルフ, GRIEGER Björn, STENZEL Oliver J.
- 日本学術振興会：特別研究員奨励費研究期間 : 2008年10月 -2010年10月代表者 : グレーベ ラルフ, セディック ハキム
- 過去と将来の気候における南極氷床の変動と力学的挙動に関する数値シミュレーション低温科学研究所：リーダーシップ研究助成研究期間 : 2009年04月 -2010年03月代表者 : グレーベ ラルフ, 杉山 慎, 阿部 彩子, 藤田 秀二, HUMBERT Angelika, KIRCHNER Nina, 本山 秀明, 齋藤 冬樹, セディック ハキム, ZWINGER Thomas
- 日本学術振興会：科研費基盤研究（B)研究期間 : 2006年04月 -2009年03月代表者 : グレーベ ラルフ, 杉山 慎This project dealt with two hot topics in current climatological research on ice sheets, induced anisotropy and fast ice flow, by means of numerical modelling. A new versatile, three-dimensional computer model "Elmer/Ice" for flowing ice masses was developed, which solves the full-Stokes equations. Within Elmer/Ice, induced anisotropy is described by the "CAFFE model". The CAFFE model was applied to the site of the EDML ice core at Kohnen Station in east Antarctica, for which the measured surface velocity and fabrics profile could be reproduced well. Elmer/Ice with the CAFFE model was applied to a 200×200km window around the Dome Fuji ice core in central east Antarctica. The main findings of the simulations were : (i)the flow regime at Dome Fuji is a complex superposition of vertical compression, horizontal extension and bed-parallel shear ; (ii)for a geothermal heat flux of 60mW m^<-2> the basal temperature at Dome Fuji reaches the pressure melting point ; (iii)the fabric shows a weak single maximum at Dome Fuji ; (iv)the basal age is smaller where the ice is thicker and larger where the ice is thinner. As a spin-off study, Elmer/Ice was also applied to the Gorshkov crater glacier at Ushkovsky volcano, Kamchatka, which is characterized by an unusually large aspect ratio and a very high geothermal heat flux. Simulations of the Greenland ice sheet were carried out with R. Greve's ice-sheet model SICOPOLIS. It was found that(i)the present-day North-East Greenland Ice Stream(NEGIS)shows basal sliding enhancement by the factor three compared to the surrounding, slowly flowing ice, and(ii)ice-dynamical processes(basal sliding accelerated by surface meltwater)can speed up the decay of the ice sheet significantly, but not catastrophically in the 21st century and beyond. Modelling with Elmer/Ice of the flow regime of the Antarctic drainage system from Dome Fuji to Shirase Glacier is still ongoing. One doctoral thesis(Mr. Hakime Seddik)and one master thesis(Ms. Shoko Otsu)were completed at Hokkaido University within this project.
- 気候変動に伴う火星の極氷床の進化と動力学低温科学研究所：リーダーシップ研究助成研究期間 : 2005年04月 -2007年03月代表者 : グレーベ ラルフ, GRIEGER Björn, STENZEL Oliver J.
- 日本学術振興会：科学研究費助成事業 学術創成研究費研究期間 : 2002年04月 -2007年03月代表者 : 本堂 武夫, グレーベ ラルフ, 飯塚 芳徳, 藤田 秀二, 堀 彰, 亀田 貴雄, 白岩 孝行, 成田 英器本研究は、氷床における様々な微物理過程と巨視的な氷床過程を融合する新たな研究領域として、Nanoglaciologyを創成すると共に、各地で採取された氷コアの高分解能解析を実施し、種々のシグナルの意味と信頼性を明らかにすることを目的として行われた。当初設定した研究課題をほぼすべて達成し、課題によっては当初想定以上の成果を挙げることができた。研究成果の要点は以下の通りである。 1.表層における物質移動と成層構造の形成過程:種々の手法を複合的に駆使して、フィルンにおける圧密過程と表層の層構造が深部に伝搬するメカニズムを明らかにした。また、SEM-EDSおよび顕微RAMANを用いて、イオン種の大部分が硫酸塩などの塩として固体微粒子の状態で存在し、塩生成反応の最終生成物とイオンバランスの関係を反応生成ダイヤグラムとしてまとめて表現できることを示した。 2.気泡-ハイドレート遷移過程と気体分別:深部で気泡からクラスレート・ハイドレートに遷移する過程で、ハイドレートの新たな核生成過程を明らかにし、ハイドレートの層状分布が堆積微粒子の季節変動を反映することを示した。また、ハイドレートの成長過程と気体分別およびそれらが大気組成データに与える影響を明らかにした。 3.結晶組織の発達過程と氷床流動:これまでの流動モデルで無視されてきた結晶方位分布の異方性を取り込んだ流動モデルの定式化を行った。このモデルを南極DML地点に適用すると、異方性を考慮した場合、水平流動速度は数倍大きくなり、この異方性の効果が極めて大きいことを示した。 4.氷床における電波伝播特性とレーダー探査:氷床内部の酸性不純物層や氷結晶組織の異方性分布を探査する新たなレーダーシステムによって、氷床内部の結晶組織分布などの画期的な情報抽出に成功し、氷コアによる1地点のデータを広域に拡大すること、および上記流動モデルとの対比を可能にした。
教育活動情報
主要な担当授業
- 理論雪氷学特論開講年度 : 2021年課程区分 : 修士課程開講学部 : 環境科学院キーワード : 氷床、氷河、棚氷、流れ、動?学、連続体?学 Ice sheet, glacier, ice shelf, flow, dynamics, continuum mechanics
- 大学院共通授業科目（教育プログラム）：南極学開講年度 : 2021年課程区分 : 修士課程開講学部 : 大学院共通科目キーワード : 野外観測、降雪、積雪、気象、水文
- 国際科学ｺﾐｭﾆｹｰｼｮﾝ法特論開講年度 : 2021年課程区分 : 修士課程開講学部 : 環境科学院キーワード : 科学英語、英文作成、英語での研究発表、英語での議論 Scientific English, writing, presentation, discussion
- 地球雪氷学基礎論開講年度 : 2021年課程区分 : 修士課程開講学部 : 環境科学院キーワード : 雪氷・寒冷圏、雪、氷、極地 cryosphere, snow, ice, polar regions
大学運営
委員歴
- 2019年01月 - 現在 国際雪氷学会 Journal of Glaciology 副編集長
- 2004年01月 - 現在 北海道大学低温科学研究所 教授会の委員
- 2004年01月 - 現在 北海道大学低温科学研究所 運営委員会の委員
- 2017年06月 - 2019年05月 日本雪氷学会 Bulletin of Glaciological Research 編集委員
- 1998年01月 - 2018年12月 国際雪氷学会 Journal of Glaciology 編集委員
- 2014年04月 - 2018年03月 北海道大学大学院環境科学院 EPEES運営委員会の委員
- 2008年01月 - 2017年10月 国際雪氷学会 編集委員会の委員
- 2016年04月 - 2017年03月 北海道大学低温科学研究所 低温科学第75巻 編集委員長
- 2015年03月 - 2015年12月 北海道大学低温科学研究所 低温科学国際シンポジウム実行委員会の委員長
- 2007年06月 - 2015年06月 International Association of Cryospheric Sciences Head of the Division "Planetary and Other Ices in the Solar System"
- 2005年01月 - 2014年12月 国際雪氷学会 指名委員会の委員
- 2013年04月 - 2014年06月 国立極地研究所 / Elsevier Polar Science 客員編集委員
- 2012年11月 - 2014年06月 ヨーロッパ地球科学連合 Climate of the Past と The Cryosphere 客員編集委員
- 2010年01月 - 2011年08月 国際雪氷学会 Annals of Glaciology 52(58) 編集委員
- 2007年01月 - 2011年06月 ヨーロッパ地球科学連合 The Cryosphere 編集委員
- 2010年06月 - 2010年08月 国際雪氷学会 任命された評議会の委員
- 2005年12月 - 2006年06月 国際雪氷学会 任命された評議会の委員
社会貢献活動
- 期間 : 2024年03月07日役割 : 講師主催者・発行元 : 国際雪氷学会イベント・番組・新聞雑誌名 : IGS Global Seminarオンライン期間 : 2021年10月13日役割 : 講師主催者・発行元 : 国際雪氷学会イベント・番組・新聞雑誌名 : IGS Global Seminarオンライン期間 : 2019年09月25日役割 : 司会主催者・発行元 : 北海道大学イベント・番組・新聞雑誌名 : KAKENHI Seminar in English北海道大学創生科学研究棟期間 : 2018年09月25日役割 : 司会主催者・発行元 : 北海道大学イベント・番組・新聞雑誌名 : KAKENHI Seminar in English北海道大学創生科学研究棟期間 : 2017年10月03日役割 : 司会主催者・発行元 : 北海道大学イベント・番組・新聞雑誌名 : KAKENHI Seminar in English北海道大学シオノギ創薬イノベーションセン ターHow to write strong KAKENHI proposals期間 : 2016年09月21日役割 : 司会主催者・発行元 : 北海道大学イベント・番組・新聞雑誌名 : KAKENHI Seminar in English北海道大学創生科学研究棟Tips for writing strong KAKENHI proposals期間 : 2016年07月25日役割 : 講師主催者・発行元 : ユーラクセス・ジャパンイベント・番組・新聞雑誌名 : Boost your Career: Grants in Practice駐日欧州連合代表部、東京Practical tips on writing proposals期間 : 2015年09月24日役割 : 司会主催者・発行元 : 北海道大学イベント・番組・新聞雑誌名 : KAKENHI Seminar in English北海道大学学術交流会館How to give a great scientific presentation期間 : 2014年07月14日役割 : 司会主催者・発行元 : English Engineering Education (e3) Program北海道大学工学部Ice sheets and climate change期間 : 2014年05月18日役割 : 講師主催者・発行元 : 千歳科学技術大学イベント・番組・新聞雑誌名 : 4th meeting of the German JSPS Club in Japan研究者 千歳科学技術大学Global warming and icy environments期間 : 2008年11月15日役割 : 司会主催者・発行元 : 北海道大学CoSTEPイベント・番組・新聞雑誌名 : International Science Cafeレストラン「みんたる」、札幌
メディア報道
- Geoengineering may slow Greenland ice sheet loss報道 : 2024年01月30日発行元・放送局 : Hokkaido University番組・新聞雑誌 : Research Press Releaseインターネットメディア
- 成層圏へのエアロゾル噴射による氷床の変化を予測〜グリーンランド氷床の体積減少を大幅に抑制できることが判明〜報道 : 2024年01月11日発行元・放送局 : 北海道大学番組・新聞雑誌 : プレスリリース（研究発表）インターネットメディア
- 報道 : 2022年03月25日発行元・放送局 : 北海道大学番組・新聞雑誌 : プレスリリース（研究発表）インターネットメディア
- 報道 : 2022年03月14日発行元・放送局 : Hokkaido University番組・新聞雑誌 : Research Press Releaseインターネットメディア
- 3000年に海面5.3m上昇・南極氷床の変動予測報道 : 2022年02月02日番組・新聞雑誌 : 日刊工業新聞新聞・雑誌
- 南極融解、1000年先まで？海面上昇で東京も浸水リスク報道 : 2022年01月30日番組・新聞雑誌 : 日本経済新聞新聞・雑誌
- 報道 : 2022年01月24日発行元・放送局 : 北海道大学番組・新聞雑誌 : プレスリリース（研究発表）インターネットメディア
- 報道 : 2021年12月22日発行元・放送局 : Hokkaido University番組・新聞雑誌 : Research Press Releaseインターネットメディア
- 報道 : 2020年11月12日発行元・放送局 : Hokkaido University番組・新聞雑誌 : Research Press Releaseインターネットメディア
- 報道 : 2020年09月17日発行元・放送局 : Hokkaido University番組・新聞雑誌 : Research Press ReleaseJapan インターネットメディア
学術貢献活動
- Fast Glacier Flow: Processes, Observations and Modelling of Ice Streams, Tidewater Glaciers and Surging Glaciers期間 : 2019年07月10日役割 : パネル司会・セッションチェア等種別 : 大会・シンポジウム等主催者・責任者 : International Union of Geodesy and Geophysics (IUGG)Montreal, Canada Co-convenor of session C05 "Fast Glacier Flow: Processes, Observations and Modelling of Ice Streams, Tidewater Glaciers and Surging Glaciers", IUGG General Assembly
- Cold Flows期間 : 2016年06月06日役割 : パネル司会・セッションチェア等種別 : 大会・シンポジウム等主催者・責任者 : International Union of Geodesy and Geophysics (IUGG)Paris, France Co-convenor of session 2d "Cold Flows", IUGG Conference on Mathematical Geophysics
- ILTS International Symposium on Low Temperature Science期間 : 2015年11月30日 - 2015年12月02日役割 : 企画立案・運営等種別 : 大会・シンポジウム等主催者・責任者 : 低温科学研究所札幌 Head of the Local Organizing Committee, ILTS International Symposium on Low Temperature Science
- Planetary Physics期間 : 2015年06月26日役割 : パネル司会・セッションチェア等種別 : 大会・シンポジウム等主催者・責任者 : International Union of Geodesy and Geophysics (IUGG)Prague, Czechia Co-convenor of session JS1 "Planetary Physics", IUGG General Assembly
- Solar System Exploration of Atmospheres with Ground-Based and Space-Based Platforms期間 : 2015年06月24日役割 : パネル司会・セッションチェア等種別 : 大会・シンポジウム等主催者・責任者 : International Union of Geodesy and Geophysics (IUGG)Prague, Czechia Co-convenor of session M09 "Solar System Exploration of Atmospheres with Ground-Based and Space-Based Platforms", IUGG General Assembly,
- Linking Cryospheric Observations and Modeling期間 : 2014年12月19日役割 : パネル司会・セッションチェア等種別 : 大会・シンポジウム等主催者・責任者 : American Geophysical Union (AGU)San Francisco, USA Co-convenor of session C51B/C54A "Linking Cryospheric Observations and Modeling", AGU Fall Meeting