研究者データベース

富田 裕之(トミタ ヒロユキ)
地球環境科学研究院 地球圏科学部門 大気海洋物理学分野
准教授

基本情報

所属

  • 地球環境科学研究院 地球圏科学部門 大気海洋物理学分野

職名

  • 准教授

学位

  • 博士(工学)(東海大学)

ホームページURL

Researcher ID

  • AAA-3635-2019

J-Global ID

プロフィール

研究キーワード

  • 衛星観測   海面フラックス   海面熱フラックス   大気海洋相互作用   リモートセンシング   海面水温   気候変動   熱帯低気圧   台風   

研究分野

  • 自然科学一般 / 大気水圏科学

職歴

  • 2021年04月 - 現在 北海道大学 大学院地球環境科学研究院
  • 2016年04月 - 2021年03月 名古屋大学 宇宙地球環境研究所 特任助教
  • 2012年04月 - 2016年03月 名古屋大学 地球水循環研究センター 拠点研究員
  • 2009年04月 - 2012年03月 海洋研究開発機構 地球環境変動領域 研究技術専任スタッフ
  • 2006年04月 - 2009年03月 海洋研究開発機構 地球環境観測センター ポスドク研究員
  • 2004年04月 - 2006年03月 東海大学 非常勤助手

学歴

  • 2001年04月 - 2004年03月   東海大学大学院   海洋学研究科 博士課程後期
  • 1999年04月 - 2001年03月   東海大学大学院   海洋学研究科 博士課程前期
  • 1995年04月 - 1999年03月   東海大学   海洋学部 海洋工学科

研究活動情報

論文

  • Hiroyuki Tomita, Meghan F. Cronin, Shun Ohishi
    Scientific Reports 11 1 2021年12月 [査読有り]
     
    AbstractThis study aims to identify patterns of surface heat fluxes, and corresponding surface ocean responses, associated with synoptic-scale atmospheric events and their modulation on seasonal time scales. In particular, northerly and southerly wind events associated with atmospheric disturbances were analyzed using high-temporal resolution time-series data from two moored buoys (JKEO: 2007–2010 and KEO: 2004–2019) north and south of the Kuroshio Extension current. Although each synoptic-scale wind event generally impacted both sites, the composite surface heat flux was larger at the northern site, especially for northerly events. Both types of wind events were observed throughout the year, with a minimum during June-July–August. Northerly wind events tended to be accompanied by lowered air-temperature, while southerly events tended to have elevated air-temperature relative to the previous three days. The resulting anomalous surface heat loss was asymmetric, with larger changes in northerly events compared to the southerly events. A large and significant ocean response of − 0.28 to − 0.46 K (p-value < 0.05) in SST was confirmed only for northerly events in spring–summer at the northern site, while smaller changes were found at the southern site. The results of this study suggest that sub-monthly air-sea interactions may affect seasonal variability and potentially climate change over longer timescales.
  • Hiroyuki Tomita, Kunio Kutsuwada, Masahisa Kubota, Tsutomu Hihara
    Frontiers in Marine Science 8 2021年02月05日 [査読有り]
     
    The reliability of surface net heat flux data obtained from the latest satellite-based estimation [the third-generation Japanese Ocean Flux Data Sets with Use of Remote Sensing Observations (J-OFURO3, V1.1)] was investigated. Three metrics were utilized: (1) the global long-term (30 years) mean for 1988–2017, (2) the local accuracy evaluation based on comparison with observations recorded at buoys located at 11 global oceanic points with varying climatological characteristics, and (3) the physical consistency with the freshwater balance related to the global water cycle. The globally averaged value of the surface net heat flux of J-OFURO3 was −22.2 W m−2, which is largely imbalanced to heat the ocean surface. This imbalance was due to the turbulent heat flux being smaller than the net downward surface radiation. On the other hand, compared with the local buoy observations, the average difference was −5.8 W m−2, indicating good agreement. These results indicate a paradox of the global surface net heat flux. In relation to the global water cycle, the balance between surface latent heat flux (ocean evaporation) and precipitation was estimated to be almost 0 when river runoff from the land was taken into consideration. The reliability of the estimation of the latent heat flux was reconciled by two different methods. Systematic ocean-heating biases by surface sensible heat flux (SHF) and long wave radiation were identified. The bias in the SHF was globally persistent and especially large in the mid- and high latitudes. The correction of the bias has an impact on improving the global mean net heat flux by +5.5 W m−2. Furthermore, since J-OFURO3 SHF has low data coverage in high-latitudes areas containing sea ice, its impact on global net heat flux was assessed using the latest atmospheric reanalysis product. When including the sea ice region, the globally averaged value of SHF was approximately 1.4 times larger. In addition to the bias correction mentioned above, when assuming that the global ocean average of J3 SHF is 1.4 times larger, the net heat flux value changes to the improved value (−11.3 W m−2), which is approximately half the original value (−22.2 W m−2).
  • Akiyoshi Wada, Hiroyuki Tomita, Shin’ichiro Kako
    Journal of Oceanography 76 6 419 - 437 2020年12月 [査読有り]
     
    Abstract Insufficient in situ observations in high winds make it difficult to verify climatological data sets and the results of tropical cyclone (TC) simulations. Reliable data sets are necessary for developing numerical models that predict TCs more accurately. This study attempted to compare the third-generation Japanese Ocean Flux Data Sets with Use of Remote-Sensing Observations (J-OFURO3) data, with TC simulations conducted by a 2 km mesh coupled atmosphere-wave-ocean model. This is a case study of Typhoon Dujuan (2015) and the area of approximately 20̊N, 130̊E, south of Okinawa, was selected. The comparison reveals that J-OFURO3 data are reliable for verifying the atmospheric and oceanic components of TC simulations with two different initial sea surface temperature (SST) conditions, although the blank area remains within the inner core area for air temperature, specific humidity, and latent heat flux owing to issues with the construction method. Simulated maximum surface wind speeds (MSWs) are significantly correlated with J-OFURO3 MSWs. The asymmetrical distribution of simulated surface wind speeds within the inner core area can be reproduced well in the J-OFURO3 data set. In terms of the oceanic response to the TC, TC-induced sea surface cooling was reproduced well in the J-OFURO3 data set and is consistent with the simulation results. Unlike simulated SST, simulated surface wind speeds, surface air temperature, and surface specific humidity are still inconsistent with the J-OFURO3 data, even when the J-OFURO3 SST is used as the initial condition. New algorithms, more satellite data used, and model improvement are expected in the future.
  • Franklin R. Robertson, Jason B. Roberts, Michael G. Bosilovich, Abderrahim Bentamy, Carol Anne Clayson, Karsten Fennig, Marc Schröder, Hiroyuki Tomita, Gilbert P. Compo, Marloes Gutenstein, Hans Hersbach, Chiaki Kobayashi, Lucrezia Ricciardulli, Prashant Sardeshmukh, Laura C. Slivinski
    Journal of Climate 33 19 8415 - 8437 2020年10月01日 [査読有り]
     
    AbstractFour state-of-the-art satellite-based estimates of ocean surface latent heat fluxes (LHFs) extending over three decades are analyzed, focusing on the interannual variability and trends of near-global averages and regional patterns. Detailed intercomparisons are made with other datasets including 1) reduced observation reanalyses (RedObs) whose exclusion of satellite data renders them an important independent diagnostic tool; 2) a moisture budget residual LHF estimate using reanalysis moisture transport, atmospheric storage, and satellite precipitation; 3) the ECMWF Reanalysis 5 (ERA5); 4) Remote Sensing Systems (RSS) single-sensor passive microwave and scatterometer wind speed retrievals; and 5) several sea surface temperature (SST) datasets. Large disparities remain in near-global satellite LHF trends and their regional expression over the 1990–2010 period, during which time the interdecadal Pacific oscillation changed sign. The budget residual diagnostics support the smaller RedObs LHF trends. The satellites, ERA5, and RedObs are reasonably consistent in identifying contributions by the 10-m wind speed variations to the LHF trend patterns. However, contributions by the near-surface vertical humidity gradient from satellites and ERA5 trend upward in time with respect to the RedObs ensemble and show less agreement in trend patterns. Problems with wind speed retrievals from Special Sensor Microwave Imager/Sounder satellite sensors, excessive upward trends in trends in Optimal Interpolation Sea Surface Temperature (OISST AVHRR-Only) data used in most satellite LHF estimates, and uncertainties associated with poor satellite coverage before the mid-1990s are noted. Possibly erroneous trends are also identified in ERA5 LHF associated with the onset of scatterometer wind data assimilation in the early 1990s.
  • Ayumi Koizumi, Masahisa Kubota, Kunio Kutsuwada, Tsutomu Hihara, Hiroyuki Tomita
    International Journal of Remote Sensing 41 15 5770 - 5784 2020年08月02日 [査読有り]
  • Meghan F. Cronin, Chelle L. Gentemann, James Edson, Iwao Ueki, Mark Bourassa, Shannon Brown, Carol Anne Clayson, Chris W. Fairall, J. Thomas Farrar, Sarah T. Gille, Sergey Gulev, Simon A. Josey, Seiji Kato, Masaki Katsumata, Elizabeth Kent, Marjolaine Krug, Peter J. Minnett, Rhys Parfitt, Rachel T. Pinker, Paul W. Stackhouse, Sebastiaan Swart, Hiroyuki Tomita, Douglas Vandemark, A. Robert Weller, Kunio Yoneyama, Lisan Yu, Dongxiao Zhang
    Frontiers in Marine Science 6 2019年07月31日 [査読有り]
  • Hiroyuki Tomita, Tsutomu Hihara, Shin'ichiro Kako, Masahisa Kubota, Kunio Kutsuwada
    JOURNAL OF OCEANOGRAPHY 75 2 171 - 194 2019年04月 [査読有り][通常論文]
     
    Accurate observational estimation of the ocean surface heat, momentum, and freshwater fluxes is crucial for studies of the global climate system. Estimating surface flux using satellite remote sensing techniques is one possible answer to this challenge. In this paper, we introduce J-OFURO3, a third-generation data set developed by the Japanese Ocean Flux Data Sets with Use of Remote-Sensing Observations (J-OFURO) research project, which represents a significant improvement from older data sets as the result of research and development conducted from several perspectives. J-OFURO3 offers data sets for surface heat, momentum, freshwater fluxes, and related parameters over the global oceans (except regions of sea ice) from 1988 to 2013. The surface flux data, based on a 0.25A degrees grid system, have a higher spatial resolution and are more accurate than the previous efforts. This has been achieved through the adopting of the state-of-the-art algorithms that estimate the near-surface air specific humidity and the improvement of techniques using observations from multi-satellite sensors. Comparisons with in situ observations using a systematic system developed along with the J-OFURO3 data set confirmed these improvements in accuracy, as did comparisons with other data sets. J-OFURO3 data are of good quality, facilitating a clearer understanding of more fine-scale ocean-atmosphere features (such as ocean fronts, mesoscale eddies, and geographic features) and their effects on surface fluxes. The information contained in this long-term (26 year) data set is demonstrably beneficial to understanding climate change and its relationship to oceans and the atmosphere.
  • Tsujino Hiroyuki, Urakawa Shogo, Nakano Hideyuki, Small R. Justin, Kim Who M, Yeager Stephen G, Danabasoglu Gokhan, Suzuki Tatsuo, Bamber Jonathan L, Bentsen Mats, Boening Claus W, Bozec Alexandra, Chassignet Eric P, Curchitser Enrique, Dias Fabio Boeira, Durack Paul J, Griffes Stephen M, Harada Yayoi, Ilicak Mehmet, Josey Simon A, Kobayashi Chiaki, Kobayashi Shinya, Komuro Yoshiki, Large William G, Le Sommer Julien, Marsl, Simon J, Masina Simona, Scheinert Markus, Tomita Hiroyuki, Valdivieso Maria, Yamazaki Dai
    OCEAN MODELLING 130 79 - 139 2018年10月 [査読有り][通常論文]
  • Maure E. R, Ishizaka J, Aiki H, Mino Y, Yoshie N, Goes J. I, Gomes H. R, Tomita H
    JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 123 9 6841 - 6860 2018年09月 [査読有り][通常論文]
  • H. Tomita, T. Hihara, M. Kubota
    Geophysical Research Letters 45 2 899 - 906 2018年01月28日 [査読有り][通常論文]
     
    Near-surface air-specific humidity is a key variable in the estimation of air-sea latent heat flux and evaporation from the ocean surface. An accurate estimation over the global ocean is required for studies on global climate, air-sea interactions, and water cycles. Current remote sensing techniques are problematic and a major source of errors for flux and evaporation. Here we propose a new method to estimate surface humidity using satellite microwave radiometer instruments, based on a new finding about the relationship between multichannel brightness temperatures measured by satellite sensors, surface humidity, and vertical moisture structure. Satellite estimations using the new method were compared with in situ observations to evaluate this method, confirming that it could significantly improve satellite estimations with high impact on satellite estimation of latent heat flux. We recommend the adoption of this method for any satellite microwave radiometer observations.
  • E. R. Maure, J. Ishizaka, C. Sukigara, Y. Mino, H. Aiki, T. Matsuno, H. Tomita, J. I. Goes, H. R. Gomes
    GEOPHYSICAL RESEARCH LETTERS 44 21 11115 - 11124 2017年11月 [査読有り][通常論文]
     
    Satellite Chlorophyll a (CHL) data were used to investigate the influence of mesoscale anticyclonic eddies (AEs) and cyclonic eddies (CEs) on the timing of spring phytoplankton bloom initiation around the Yamato Basin (133-139 degrees E and 35-39.5 degrees N) in the Japan Sea, for the period 2002-2011. The results showed significant differences between AEs and CEs in the timing and initiation mechanism of the spring phytoplankton bloom. Blooms were initiated earlier in CEs which were characterized by shallow mixed-layer depths (< 100 m). The early blooming preceded the end of winter cooling (i.e., while net heat flux (Q(0)) is still negative) and is initiated by the increased average light within the shallow mixed-layer depth. Conversely, blooms appeared in the AEs despite deeper mixed-layer depth (> 100 m) but close to the commencement of positive Q(0). This suggests that the relaxation of turbulent mixing is crucial for the bloom initiation in AEs.
  • Tomoki Tozuka, Meghan F. Cronin, Hiroyuki Tomita
    SCIENTIFIC REPORTS 7 2017年08月 [査読有り][通常論文]
     
    Western boundary currents bring warm tropical water poleward and eastward and are characterized by a sharp sea surface temperature (SST) front on the poleward edge of the current as it extends into the interior basin. One of the most prominent such front is associated with the Kuroshio Extension (KE) as it extends east of Japan ("upstream KE"). Large latent and sensible heat fluxes that warm the atmosphere and cool the ocean project this front into the atmosphere, thereby affecting weather and climate both locally and remotely. While one might assume that these larger surface heat fluxes on the equatorward side would tend to damp the SST front, here we present observational evidence that the surface heat loss actually strengthens the front during October-April in monthly climatology and about 87% of months from October to January during the 2004/05-2014/15 period, although the percentage lowers to about 38% for February-April of the same period, suggesting some temporal/data dependency in the analysis. The key to understanding this counterintuitive result for frontogenesis is that the effective heat capacity of the surface water depends on mixed layer thickness. SSTs are more (less) sensitive to surface heat fluxes in regions with shallow (deep) mixed layer.
  • Meghan F. Cronin, Nicholas A. Bond, J. Thomas Farrar, Hiroshi Ichikawa, Steven R. Jayne, Yoshimi Kawai, Masanori Konda, Bo Qiu, Luc Rainville, Hiroyuki Tomita
    Deep-Sea Research Part II: Topical Studies in Oceanography 132 263 - 264 2016年10月01日 [査読有り][通常論文]
     
    The authors regret that Fig. 8 bottom panel had a 0.1 offset applied to the buoyancy frequency (N). This plotting error did not affect any other aspect of the original paper. The correctly plotted Fig. 8 is shown below.
  • Hiroyuki Tomita, Tomoharu Senjyu, Masahisa Kubota
    JOURNAL OF OCEANOGRAPHY 72 5 747 - 760 2016年10月 [査読有り][通常論文]
     
    In order to evaluate the air-sea sensible and latent heat fluxes (SHF and LHF, respectively) over the Japan Sea obtained from satellite-derived, atmospheric reanalysis, and objective analysis products, we conducted an intercomparison of climatological monthly mean fields and a validation of the daily means with in situ observations. As a result, we found significant differences in the climatological mean fields of SHF in products during the winter. The SHF values from the Japanese Ocean Flux Data Sets with Use of Remote Sensing Observations version 2 (J-OFURO2) showed finer-scale spatial structures, large values near the coastal regions, and small values over the center of the Japan Sea. From a comparison with in situ observations, we concluded that J-OFURO2 SHF has better performance compared with the other global products. The differences in LHF in the products are not so large compared with the results for SHF. However, in a comparison between the satellite-derived products and the others, the representations of the frontal features associated with the sub-polar front and the Tsushima warm current were different. A comparison in the near-coastal region showed that application of the creeping-sea-fill technique used in J-OFURO2 provided appropriate data in the region and succeeded in reducing the adverse effects from land contamination encountered when using coarse atmospheric reanalysis data.
  • Shigeki Hosoda, Masami Nonaka, Tomohiko Tomita, Bunmei Taguchi, Hiroyuki Tomita, Naoto Iwasaka
    JOURNAL OF OCEANOGRAPHY 71 5 541 - 556 2015年10月 [査読有り][通常論文]
     
    Observational data are used to investigate summer heat penetration into the subsurface ocean in order to quantify the heat capacity of the upper ocean with respect to surface heat exchange. Sea surface temperature is strongly modulated by the change in heat capacity, which could influence the overlying atmosphere and hence trigger climate variations, even during the warming season, when the ocean has been regarded as being rather passive. Few studies have focused on the heat exchange process in surface and subsurface layers because of the existence of a strong seasonal thermocline at the bottom of thin summer mixed layers (ML). By introducing the concept of the heat penetration depth (HPD), defined as the depth to which the downward net heat flux (Q (net)) distinctly penetrates, we here characterize the heat capacity in terms of the heat content above the HPD using a simple, one-dimensional vertical model during the warming season. Seasonal changes in the HPD indicate that the thermal effects of Q (net) gradually penetrate below the shallow seasonal thermocline due to vertical eddy diffusivity. Downward heat penetration into the layer below the shallow seasonal thermocline occurs widely throughout the North Pacific, and two-thirds of Q (net) penetrates below the ML. In a hypothetical analysis of the case where the observed Q (net) accumulates only within the ML, the change in SST is unrealistically larger than that of the observed SST. These results indicate that heat penetration plays a crucial role in climate variations during the warming season.
  • Hiroyuki Tomita, Yoshimi Kawai, Meghan F. Cronin, Tsutomu Hihara, Masahisa Kubota
    SOLA 11 43 - 47 2015年 [査読有り][通常論文]
     
    The Global Change Observation Mission-Water "Shizuku" (GCOM-W) satellite, with a newly developed microwave radiometer: Advanced Microwave Scanning Radiometer-2 (AMSR2) developed by Japan Aerospace Exploration Agency, was launched successfully in May 2012. The standard geophysical products of AMSR2/GCOM-W were released a year after launch date. Here, we use data from three buoys moored in the Kuroshio Extension region to test the accuracy of AMSR2 sea surface temperature (SST) and near surface wind speed (SSW). The Kuroshio Extension region is subject to large multi-scale variability and intense air-sea interaction and thus provides a challenging test for the satellite sensor. From the year-long comparison, we confirm that the root mean square difference (RMSD) of AMSR2 SST observations was 0.75 degrees C and meets the criterion for release accuracy (0.8 degrees C). On the other hand, the RMSD of SSW was 1.6 in s(-1), slightly worse than the criterion (1.5 in s(-1)), suggesting that the algorithm for SSW needs to be further improved. The analysis also showed that seasonal variations and characteristics of the relationship between SST and SSW are similar to those observed by previous satellite sensor (AMSR-E). Overall, the results give confidence that AMSR2 products can be used for many air-sea interaction, climate, and water cycle studies.
  • Yoshimi Kawai, Hiroyuki Tomita, Meghan F. Cronin, Nicholas A. Bond
    Journal of Geophysical Research 119 13 8015 - 8031 2014年07月16日 [査読有り][通常論文]
     
    Several research cruises were conducted across the Kuroshio Extension front to examine the low-level atmospheric responses to mesoscale variations in sea surface temperature (SST). Surface meteorological observations, including sea level pressure (SLP) and SST, were collected at two moored buoys that were located on either side of the Kuroshio Extension, and from a research vessel, as it moved between the two buoys during the various cruises. Spatial perturbations in SLP along the ship transects, calculated by subtracting moored-buoy SLP from that of the moving ship, tend to be positive (negative) where SST is lower (higher) on spatial scales of about 100 km, and the magnitude of these SLP perturbations near the SST front can exceed 1.0 hPa. Radiosonde data also show that the atmospheric boundary layer thins (thickens) over lower (higher) SST. Although the contribution of across-track component in the wind cannot be calculated, the along-track component of divergence suggests low-level convergence over higher SST. The thermally induced pressure gradient is important in the momentum budget, suggesting that sea breeze-like local circulations formed over the SST fronts. Indeed, the pressure adjustment mechanism can sometimes dominate even on a scale of 100 km, although it is not always observed. The time scale in which the boundary layer thickness adjusted to SST is estimated to be 1 day or less.
  • Atsushi Okuro, Masahisa Kubota, Hiroyuki Tomita, Tsutomu Hihara
    INTERNATIONAL JOURNAL OF REMOTE SENSING 35 14 5394 - 5410 2014年 [査読有り][通常論文]
     
    In this study, eight global sea surface temperature (SST) products for 2009 are compared to clarify their characteristics. The median of eight daily values, the Ensemble Median as Reference Product (EMRP), is used as a reference product for inter-comparison. The results show that the absolute value of mean differences and the value of root mean square (RMS) differences are higher in single-microwave products such as Advanced Microwave Scanning Radiometer for the Earth observing system (AMSR-E), Tropical Rainfall Measuring Mission Microwave Imager (TMI), and WindSat, than in products such as MicroWave Optimally Interpolated SST (MWOI), Merged satellite and in situ data Global Daily SST (MGD), and Operational Sea Surface Temperature and Sea Ice Analysis (OSTIA) constructed by merging several SST data. It is of note that the characteristics of SST products depend on the type of SST used within the product, rather than the data source used. A comparison of SST products was also conducted using EMRP and data observed by moored buoys. The results show that only AMSR-E has a warm bias (+ 0.06 degrees C) while other products have a cool bias (maximum value -0.10 degrees C). The RMS error of TMI is the highest (0.57 degrees C), and that of EMRP the lowest (0.28 degrees C). Furthermore, the temporal variability between the data in each SST product was compared to those observed by the Kuroshio Extension Observatory (KEO) buoy. Results show that the temporal variability of EMRP corresponds well to that of buoy data, and that the RMS error of EMRP is lower than that of the other SST products.
  • Hiroyuki Tomita, Shang-Ping Xie, Hiroki Tokinaga, Yoshimi Kawai
    JOURNAL OF CLIMATE 26 23 9393 - 9398 2013年12月 [査読有り][通常論文]
     
    A unique set of observations on board research vessel (R/V) Mirai in April 2010 captured a striking cloud hole over a cold meander of the Kuroshio Extension (KE) east of Japan as corroborated by atmospheric soundings, ceilometer, shipboard radiation data, and satellite cloud images. Distinct differences were also observed between the warm meander farther to the north and warm water south of the KE. The atmosphere is highly unstable over the warm meander, promoting a well-mixed marine atmospheric boundary layer (MABL) and a layer of solid stratocumulus clouds capped by a strong inversion. Over the warm water south of the KE, MABL deepens and is decoupled from the ocean surface. Scattered cumulus clouds develop as captured by rapid variations in ceilometer-derived cloud base. The results show that the meandering KE front affects the entire MABL and the clouds. Such atmospheric response can potentially intensify the baroclinicity in the lower atmosphere.
  • Meghan F. Cronin, Nicholas A. Bond, J. Thomas Farrar, Hiroshi Ichikawa, Steven R. Jayne, Yoshimi Kawai, Masanori Konda, Bo Qiu, Luc Rainville, Hiroyuki Tomita
    DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 85 62 - 74 2013年01月 [査読有り][通常論文]
     
    Data from the Kuroshio Extension Observatory (KEO) surface mooring are used to analyze the balance of processes affecting the upper ocean heat content and surface mixed layer temperature variations in the Recirculation Gyre (RG) south of the Kuroshio Extension (KE). Cold and dry air blowing across the ICE and its warm RG during winter cause very large heat fluxes out of the ocean that result in the erosion of the seasonal thermocline in the RG. Some of this heat is replenished through horizontal heat advection, which may enable the seasonal thermocline to begin restratifying while the net surface heat flux is still acting to cool the upper ocean. Once the surface heat flux begins warming the ocean, restratification occurs rapidly due to the low thermal inertia of the shallow mixed layer depth. Enhanced diffusive mixing below the mixed layer tends to transfer some of the mixed layer heat downward, eroding and potentially modifying sequestered subtropical mode water and even the deeper waters of the main thermocline during winter. Diffusivity at the base of the mixed layer, estimated from the residual of the mixed layer temperature balance, is roughly 3 x 10(-4) m(2)/s during the summer and up to two orders of magnitude larger during winter. The enhanced diffusivities appear to be due to large inertial shear generated by wind events associated with winter storms and summer tropical cyclones. The diffusivity's seasonality is likely due to seasonal variations in stratification just below the mixed layer depth, which is large during the summer when the seasonal thermocline is fully developed and low during the winter when the mixed layer extends to the top of the thermocline. Published by Elsevier Ltd.
  • Shinya Kouketsu, Hiroyuki Tomita, Eitarou Oka, Shigeki Hosoda, Taiyo Kobayashi, Kanako Sato
    JOURNAL OF OCEANOGRAPHY 68 1 63 - 77 2012年02月 [査読有り][通常論文]
     
    Distributions of mixed layer depths around the centers of anti-cyclonic and cyclonic eddies in the North Pacific Ocean were composited by using satellite-derived sea surface height anomaly data and Argo profiling float data. The composite distributions showed that in late winter, deeper mixed layers were more (less) frequently observed inside the cores of the anti-cyclonic (cyclonic) eddies than outside. This relationship was the clearest in the region of 140A degrees E-160A degrees W and 35A degrees N-40A degrees N, where the temperature and salinity of the deep mixed layers were similar to those of the lighter variety of central mode water (L-CMW). A simple one-dimensional bulk mixed layer model showed that both strong sea-surface heat and momentum fluxes and weak preexisting stratification contributed to formation of the deep mixed layer. These conditions were associated with the anti-cyclonic eddies, suggesting that these eddies are important in the formation of mode waters, particularly L-CMW.
  • Hiroyuki Tomita, Shinya Kouketsu, Eitarou Oka, Masahisa Kubota
    GEOPHYSICAL RESEARCH LETTERS 38 2011年12月 [査読有り][通常論文]
     
    Satellite-derived high-resolution air-sea flux data and Argo float data were analyzed to reveal the fine-scale spatial structures of air-sea turbulent heat and momentum fluxes and their relationship with the deep oceanic mixed layer around the subarctic front (SAF) in the North Pacific. An important feature inferred from the satellite-derived dataset is the presence of a pair of positive and negative air-sea flux anomaly bands with a width of 100-200 km on both sides of the SAF. Such a fine-scale structure in air-sea fluxes has not been captured in previous datasets. The SAF plays a significant role in determining the fine-scale structure of air-sea fluxes. The oceanic mixed layer is deeper to the south of the SAF, and the maximum mixed layer depth is observed near the positive anomaly band in air-sea fluxes. This study concludes that active air-sea interactions due to the presence of the SAF enhances upward air-sea heat and momentum fluxes to the south of SAF and selectively produces a deep oceanic mixed layer where the formation of Transition Region Mode Water occurs. Citation: Tomita, H., S. Kouketsu, E. Oka, and M. Kubota (2011), Locally enhanced wintertime air-sea interaction and deep oceanic mixed layer formation associated with the subarctic front in the North Pacific, Geophys. Res. Lett., 38, L24607, doi: 10.1029/2011GL049902.
  • H. Tomita, M. Kubota
    INTERNATIONAL JOURNAL OF REMOTE SENSING 32 12 3389 - 3404 2011年 [査読有り][通常論文]
     
    To quantify the sampling error of wind speed (W) and the surface air specific humidity (Qa) resulting from Sun-synchronous polar-orbit satellite sampling and the effect of single-and multi-satellite sampling, we compared satellite-simulated data with true daily mean data using buoy data. True daily mean data were obtained by averaging buoy data at all available times over 24 h, while satellite-simulated data were the averages of buoy data sampled at satellite passing times (once or twice each day). The difference between true and satellite-simulated data was defined as the sampling error. The sampling error of the daily mean data of W and Qa depends considerably on the satellite observation time and location. Although the sampling error is fairly reduced if multi-satellite sampling is employed, a noticeable sampling error remains in some cases if a wrong sampling combination is employed. Therefore, multi-satellite data should be carefully used to obtain more accurate global data.
  • Hiroyuki Tomita, Shin'ichiro Kako, Meghan F. Cronin, Masahisa Kubota
    JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 115 2010年12月 [査読有り][通常論文]
     
    Summertime surface heat flux and upper ocean state in 2004, 2005, and 2006 obtained from the Kuroshio Extension Observatory (KEO) buoy were investigated, focusing on the summertime preconditioning of the following winter's mixed layer. Summertime net shortwave radiation at the surface shows large year-to-year variations that resulted in anomalous heating in 2005 and anomalous cooling in 2006. Covariation of the surface heat flux and upper ocean stratification was found and suggests that year-to-year variations of summertime heat flux induce corresponding changes in the near surface stratification. Cold core rings, observed in 2006, tend to intensify both the near surface (< 100 m depth) density stratification and the density stratification below the seasonal thermocline (> 100 m depth). Lateral and vertical heat fluxes evaluated from the imbalance between the observed heat storage rate and the net heat flux and entrainment also have a significant role in determination of upper ocean stratification and can intensify year-to-year variation of the mixed layer. The physical mechanism that determines the precondition of the next winter mixed layer can change each year. In 2005, near surface stratification induced by anomalous summertime heating has a dominant role compared to deeper stratification. On the other hand, in 2006, the much deeper stratification below the seasonal thermocline (> 100 m depth) associated with cold core rings contributes to make the maximum vertical density stratification.
  • Masanori Konda, Hiroshi Ichikawa, Hiroyuki Tomita, Meghan F. Cronin
    JOURNAL OF CLIMATE 23 19 5206 - 5221 2010年10月 [査読有り][通常論文]
     
    Wintertime sea surface heat flux variability across the Kuroshio Extension (KE) front is analyzed using data from the Kuroshio Extension Observatory (KEO) buoy in the Kuroshio recirculation gyre south of the KE front and from the Japan Agency for Marine-Earth Science and Technology KEO (JKEO) buoy in the north of the front. The coincident data used are from periods during two winters (2007 and 2008), when both buoys had a complete suite of meteorological data. In these two winter periods, the focus of this research is on three types of typical weather patterns referred to here as the northerly wind condition, the monsoon wind condition, and the normal condition. During the northerly wind condition, latent and sensible heat fluxes were large and often varied simultaneously at both sites, whereas during the monsoon wind condition the latent heat flux at the KEO site was significantly larger than that at the JKEO site. The difference between these heat flux patterns is attributed to the different airmass transformations that occur when prevailing winds blow across the KE front versus along the front. Reanalysis products appear to reproduce these heat flux spatial patterns at synoptic scales. It is suggested that the relative frequencies of these different types of weather conditions result in anomalous spatial patterns in the heat fluxes on monthly time scales.
  • Akira Nagano, Kaoru Ichikawa, Hiroshi Ichikawa, Hiroyuki Tomita, Hiroki Tokinaga, Masanori Konda
    JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 115 2010年09月 [査読有り][通常論文]
     
    We conducted synoptic hydrographic surveys three times under distinctly different conditions of the Kuroshio in the region off the southern coast of Japan; the large-meander (October 2004) and non-large-meander (September 2005 and September 2006) states. As a result of the water mass analysis, we could separate the volume and heat transports of the North Pacific subtropical gyre from the local recirculation gyre and mesoscale eddies. Despite the different flow conditions of the Kuroshio, the volume transport and the volume transport-averaged temperature of the subtropical gyre fluctuate within the ranges of 23.3-29.0 x 10(6) m(3) s(-1) and 17.3-17.6 degrees C, respectively, which are quite stable with respect to those for the Kuroshio south of Japan estimated in the past studies. Taking into account the decrease in the volume transport-averaged temperature in the North Pacific interior region, the net heat transport of the subtropical gyre across the latitude of 30 degrees N was estimated to be between 0.19 and 0.22 x 10(15) W.
  • Akira Nagano, Kaoru Ichikawa, Hiroshi Ichikawa, Hiroyuki Tomita, Hiroki Tokinaga, Masanori Konda
    J. Geophys. Res. 115 C9 C09002  2010年09月 [査読有り][通常論文]
  • Shinsuke Iwasaki, Masahisa Kubota, Hiroyuki Tomita
    JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 115 2010年07月 [査読有り][通常論文]
     
    To establish the most accurate bulk method for estimating the satellite-derived latent heat flux (LHF), we evaluate four bulk methods by using direct eddy correlation and inertial dissipation fluxes obtained during 15 cruises in the tropics and midlatitudes. According to our results, the coupled ocean-atmosphere response experiment (COARE) version 3 is the best algorithm for estimating the satellite-derived LHF. Moreover, to clarify the error sources when measuring the satellite-derived LHF including errors in meteorological values, we evaluated the LHF errors as an error function of the meteorological values. If we assume that the reported RMS error for the satellite-derived meteorological values is valid, the RMS error of the LHF derived from instantaneous satellite data is estimated to be approximately 35-55 W/m(2). The error determined by the bulk method contributes to 30-50% of the RMS error of the LHF.
  • Hiroyuki Tomita, Masahisa Kubota, Meghan F. Cronin, Shinsuke Iwasaki, Masanori Konda, Hiroshi Ichikawa
    JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 115 2010年03月 [査読有り][通常論文]
     
    The daily mean air-sea heat fluxes over the global oceans have been developed as the version 2 of Japanese Ocean Flux data sets with use of Remote sensing Observations (J-OFURO2). Net heat flux is available from 1988 to 2006, and the turbulent heat flux is available from 1988 to 2007. To assess the accuracy of the J-OFURO2 product over the Kuroshio Extension region, air-sea heat fluxes and related state variables were compared with independent in situ observations from the Kuroshio Extension Observatory (KEO) and JAMSTEC KEO (JKEO) surface moorings. Although seasonal biases were found, these tended to cancel out over the total period, resulting in a total bias and RMS in J-OFURO2 net heat fluxes of 8.6 and 56.8 W/m(2), respectively. Comparisons with other global air-sea heat flux products from numerical weather prediction, i.e., the National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) reanalysis (NRA1), the NCEP/Department of Energy reanalysis (NRA2), and satellite observations, i.e., Hamburg Ocean Atmosphere Parameters and Fluxes from Satellite data and merged product, i.e., Objectively Analyzed Air-Sea Fluxes were also conducted at the KEO and JKEO sites. Comparison results show that the total and seasonal biases are smallest compared with other products, and J-OFURO2 air-sea heat fluxes are best data set for air-sea interaction study over the Kuroshio Extension region.
  • Hiroyuki Tomita, Shin'Ichiro Kako, Meghan F. Cronin, Masahisa Kubota
    Journal of Geophysical Research: Oceans 115 12 2010年 [査読有り][通常論文]
     
    Summertime surface heat flux and upper ocean state in 2004, 2005, and 2006 obtained from the Kuroshio Extension Observatory (KEO) buoy were investigated, focusing on the summertime preconditioning of the following winter's mixed layer. Summertime net shortwave radiation at the surface shows large year-to-year variations that resulted in anomalous heating in 2005 and anomalous cooling in 2006. Covariation of the surface heat flux and upper ocean stratification was found and suggests that year-to-year variations of summertime heat flux induce corresponding changes in the near surface stratification. Cold core rings, observed in 2006, tend to intensify both the near surface (< 100 m depth) density stratification and the density stratification below the seasonal thermocline (> 100 m depth). Lateral and vertical heat fluxes evaluated from the imbalance between the observed heat storage rate and the net heat flux and entrainment also have a significant role in determination of upper ocean stratification and can intensify year-to-year variation of the mixed layer. The physical mechanism that determines the precondition of the next winter mixed layer can change each year. In 2005, near surface stratification induced by anomalous summertime heating has a dominant role compared to deeper stratification. On the other hand, in 2006, the much deeper stratification below the seasonal thermocline (> 100 m depth) associated with cold core rings contributes to make the maximum vertical density stratification. Copyright 2010 by the American Geophysical Union.
  • Akira Nagano, Kaoru Ichikawa, Hiroshi Ichikawa, Hiroyuki Tomita, Hiroki Tokinaga, Masanori Konda
    Journal of Geophysical Research: Oceans 115 9 2010年 [査読有り][通常論文]
     
    We conducted synoptic hydrographic surveys three times under distinctly different conditions of the Kuroshio in the region off the southern coast of Japan the large-meander (October 2004) and non-large-meander (September 2005 and September 2006) states. As a result of the water mass analysis, we could separate the volume and heat transports of the North Pacific subtropical gyre from the local recirculation gyre and mesoscale eddies. Despite the different flow conditions of the Kuroshio, the volume transport and the volume transport-averaged temperature of the subtropical gyre fluctuate within the ranges of 23.3-29.0 × 106 m3 s-1 and 17.3-17.6°C, respectively, which are quite stable with respect to those for the Kuroshio south of Japan estimated in the past studies. Taking into account the decrease in the volume transport-averaged temperature in the North Pacific interior region, the net heat transport of the subtropical gyre across the latitude of 30°N was estimated to be between 0.19 and 0.22 × 10 15 W. © Copyright 2010 by the American Geophysical Union.
  • Hiroyuki Tomita, Masahisa Kubota, Meghan F. Cronin, Shinsuke Iwasaki, Masanori Konda, Hiroshi Ichikawa
    Journal of Geophysical Research: Oceans 115 3 2010年 [査読有り][通常論文]
     
    The daily mean air-sea heat fluxes over the global oceans have been developed as the version 2 of Japanese Ocean Flux data sets with use of Remote sensing Observations (J-OFURO2). Net heat flux is available from 1988 to 2006, and the turbulent heat flux is available from 1988 to 2007. To assess the accuracy of the J-OFURO2 product over the Kuroshio Extension region, air-sea heat fluxes and related state variables were compared with independent in situ observations from the Kuroshio Extension Observatory (KEO) and JAMSTEC KEO (JKEO) surface moorings. Although seasonal biases were found, these tended to cancel out over the total period, resulting in a total bias and RMS in J-OFURO2 net heat fluxes of 8.6 and 56.8 W/m2, respectively. Comparisons with other global air-sea heat flux products from numerical weather prediction, i.e., the National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) reanalysis (NRA1), the NCEP/Department of Energy reanalysis (NRA2), and satellite observations, i.e., Hamburg Ocean Atmosphere Parameters and Fluxes from Satellite data and merged product, i.e., Objectively Analyzed Air-Sea Fluxes were also conducted at the KEO and JKEO sites. Comparison results show that the total and seasonal biases are smallest compared with other products, and J-OFURO2 air-sea heat fluxes are best data set for air-sea interaction study over the Kuroshio Extension region. Copyright 2010 by the American Geophysical Union.
  • Hiroki Tokinaga, Youichi Tanimoto, Shang-Ping Xie, Takeaki Sampe, Hiroyuki Tomita, Hiroshi Ichikawa
    Journal of Climate 22 16 4241 - 4260 2009年08月 [査読有り][通常論文]
     
    A suite of shipboard and satellite observations are analyzed and synthesized to investigate the three-dimensional structure of clouds and influences from sea surface temperature fronts over the western North Pacific. Sharp transitions are observed across the Kuroshio Extension (KE) front in the marine atmospheric boundary layer (MABL) and its clouds. The ocean's influence appears to extend beyond the MABL, with higher cloud tops in altitude along the KE front than the surroundings. In winter, intense turbulent heat release from the ocean takes place on the southern flank of the KE front, where the cloud top penetrates above the MABL and reaches the midtroposphere. In this band of high cloud tops, frequent lightning activity is observed. The results of this study suggest a sea level pressure mechanism for which the temperature gradient in the MABL induces strong surface wind convergence on the southern flank of the KE front, deepening the clouds there. In early summer, sea fog frequently occurs on the northern flank of the subtropical KE and subarctic fronts under southerly warm advection that suppresses surface heat flux and stabilizes the surface atmosphere. Sea fog is infrequently observed over the KE front even under southerly conditions, as the warm ocean current weakens atmospheric stratification and promotes vertical mixing. The KE front produces a narrow band of surface wind convergence, helping support a broad band of upward motion at 700 hPa that is associated with the eastward extension of the baiu rainband from Japan in June-July. © 2009 American Meteorological Society.
  • KONDA Masanori, KONDA Masanori, ICHIKAWA Hiroshi, TOMITA Hiroyuki
    日本リモートセンシング学会誌 29 1 191 - 198 The Remote Sensing Society of Japan 2009年01月31日 [査読有り][通常論文]
     
    Wind speed and Latent heat flux derived by Advanced Microwave Scanning Radiometer (AMSR) for Earth Observing System (AMSR-E) on Aqua are validated using the tropical and the mid-latitude Pacific surface buoys. Obtaining the wind speed and reducing the Relative Wind Direction effect (RWD effect) according to Konda et al.(2006), the root mean square of the error of the wind speed at the mid-latitude buoys is reduced to 1.6ms-1, which is slightly worse than that validated by using Tropical Atmosphere Ocean project (TAO) data in the tropics. The validation shows that the mean error and its tendency are almost same as that of AMSR-E standard product. The combined use of the wind speed and the other AMSR-E products provides the instantaneous latent heat flux at every observation cells. We show that ambiguity of the estimation of the latent heat flux is caused by traditional way of computation from the boundary layer parameters, each of which is measured by different sun-synchronized satellites. The ambiguity caused by the time-lagged measurement of them is found to amount to -1.3±44.3Wm-2. The simultaneous measurement of boundary layer parameters can avoid it and make it possible to directly evaluate the satellite-derived latent heat flux by in situ observation.
  • Meghan F. Cronin, Christian Meinig, Christopher L. Sabine, Hiroshi Ichikawa, Hiroyuki Tomita
    IEEE SYSTEMS JOURNAL 2 3 424 - 430 2008年09月 [査読有り][通常論文]
     
    As a contribution to the Global Earth Observation System of Systems, the National Oceanic and Atmospheric Administration (NOAA) is developing surface moorings that carry a suite of field-proven and cost-effective sensors to monitor air-sea heat, moisture, and momentum fluxes, carbon dioxide uptake, and upper ocean temperature, salinity, and currents. In June 2004, an NOAA surface mooring, referred to as the Kuroshio Extension Observatory (KEO), was deployed in the Kuroshio Extension's (KE) southern recirculation gyre, approximately 300 nautical miles east of Japan. In 2006, a partnership between NOAA and the Japan Agency for Marine-Earth Science and Technology was formed that deployed a second mooring (referred to as JKEO) north of the KE jet in February 2007. KE is a region of strong currents, typhoons, and winter storms. Designing and maintaining moorings in the KE is a challenging engineering task. All data are publicly available. A subset of the data are telemetered and made available in near real time through the Global Telecommunications System and web-based data distribution systems. Data from these time-series reference sites serve a wide research and operational community and are being used for assessing numerical weather prediction analyses and reanalyses and for quantifying the air-sea interaction in this dynamic region.
  • Yoshimi Kawai, Toshimasa Doi, Hiroyuki Tomita, Hideharu Sasaki
    Journal of Geophysical Research: Oceans 113 8 2008年08月08日 [査読有り][通常論文]
     
    We investigated the long-term variability of the meridional heat transport across 24°N in the Pacific Ocean in two ways: (1) by adding the surface net heat flux to the temporal change rate of the ocean heat content (OHC) north of 24°N and (2) by integrating the product of meridional velocity and potential temperature over the 24°N section in numerical models. Decadal-scale changes with amplitudes of approximately 0.1-0.2 PW were detected consistently in the 5-year running means of the meridional heat transport in the 1980s and 1990s from these different analyses. The heat transport increased during the 1980s, which is closely linked with the change in the OHC. While both the Ekman and Kuroshio transports were responsible for the change in the 1980s, the contribution of the former was dominant. On the other hand, the variation in the Kuroshio temperature transport dominated meridional heat transport in the 1990s. The air-sea net heat fluxes of the atmospheric reanalysis data sets integrated north of 24°N increased in the 1990s, which indicates that the increase of the lateral heat transport was distributed mainly to the atmosphere, particularly in the Kuroshio and Kuroshio-Oyashio Extension (KOE) regions. However, there are also large discrepancies in the surface heat flux among the data sets. To reveal the impact of the decadal-scale changes in meridional heat transport on the atmosphere, it is crucial to obtain more accurate values for the air-sea heat exchange and OHC by using a sustainable observing system and numerical models. Copyright 2008 by the American Geophysical Union.
  • Yoshimi Kawai, Toshimasa Doi, Hiroyuki Tomita, Hideharu Sasaki
    JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 113 C8 2008年08月 [査読有り][通常論文]
     
    We investigated the long-term variability of the meridional heat transport across 24 degrees N in the Pacific Ocean in two ways: (1) by adding the surface net heat flux to the temporal change rate of the ocean heat content (OHC) north of 24 degrees N and (2) by integrating the product of meridional velocity and potential temperature over the 24 degrees N section in numerical models. Decadal-scale changes with amplitudes of approximately 0.1-0.2 PW were detected consistently in the 5-year running means of the meridional heat transport in the 1980s and 1990s from these different analyses. The heat transport increased during the 1980s, which is closely linked with the change in the OHC. While both the Ekman and Kuroshio transports were responsible for the change in the 1980s, the contribution of the former was dominant. On the other hand, the variation in the Kuroshio temperature transport dominated meridional heat transport in the 1990s. The air-sea net heat fluxes of the atmospheric reanalysis data sets integrated north of 24 degrees N increased in the 1990s, which indicates that the increase of the lateral heat transport was distributed mainly to the atmosphere, particularly in the Kuroshio and Kuroshio-Oyashio Extension (KOE) regions. However, there are also large discrepancies in the surface heat flux among the data sets. To reveal the impact of the decadal-scale changes in meridional heat transport on the atmosphere, it is crucial to obtain more accurate values for the air-sea heat exchange and OHC by using a sustainable observing system and numerical models.
  • Masahisa Kubota, Noriyasu Iwabe, Meghan F. Cronin, Hiroyuki Tomita
    Journal of Geophysical Research: Oceans 113 2 2008年02月08日 [査読有り][通常論文]
     
    Surface heat fluxes from the Kuroshio Extension Observatory (KEO) buoy are compared with surface heat fluxes from the National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research reanalysis (NRA1) and NCEP/Department of Energy reanalysis (NRA2). KEO surface measurements include downward solar and longwave radiation, wind speed and direction, relative humidity, rain rate, and air and sea surface temperature. For solar radiation, NRA2 had better agreement with KEO than NRA1. Both reanalyses underestimated shortwave radiation in summer and slightly overestimated it in winter. Turbulent surface heat fluxes are estimated with the KEO surface data using the Coupled Ocean-Atmosphere Response Experiment (COARE) version 3.0 bulk algorithm. Both NRA1 and NRA2 latent heat flux (LHF) are larger than KEO LHF, consistent with previous studies. However, the comparison shows larger errors than previously thought. Indeed, the latent heat flux bias for NRA1 is 41 W m-2 and for NRA2 is 62 W m-2 (indicating that the bias between NRA1 and NRA2 is 21 W m-2). For latent heat flux, the large bias is caused primarily by the NRA bulk flux algorithm, while the root mean square (RMS) error is caused primarily by errors in the NRA meteorological variables. The combination of the biases for each heat flux is such that total NRA heat transfer from the ocean to the atmosphere is considerably larger than observed by KEO. These results highlight the importance of maintaining in situ observations for monitoring surface heat fluxes in the Kuroshio/Kuroshio Extension regions. Copyright 2008 by the American Geophysical Union.
  • Masahisa Kubota, Noriyasu Iwabe, Meghan F. Cronin, Hiroyuki Tomita
    JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 113 C2 2008年02月 [査読有り][通常論文]
     
    Surface heat fluxes from the Kuroshio Extension Observatory (KEO) buoy are compared with surface heat fluxes from the National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research reanalysis ( NRA1) and NCEP/Department of Energy reanalysis (NRA2). KEO surface measurements include downward solar and longwave radiation, wind speed and direction, relative humidity, rain rate, and air and sea surface temperature. For solar radiation, NRA2 had better agreement with KEO than NRA1. Both reanalyses underestimated shortwave radiation in summer and slightly overestimated it in winter. Turbulent surface heat fluxes are estimated with the KEO surface data using the Coupled Ocean-Atmosphere Response Experiment (COARE) version 3.0 bulk algorithm. Both NRA1 and NRA2 latent heat flux (LHF) are larger than KEO LHF, consistent with previous studies. However, the comparison shows larger errors than previously thought. Indeed, the latent heat flux bias for NRA1 is 41 W m(-2) and for NRA2 is 62 W m(-2) (indicating that the bias between NRA1 and NRA2 is 21 W m(-2)). For latent heat flux, the large bias is caused primarily by the NRA bulk flux algorithm, while the root mean square (RMS) error is caused primarily by errors in the NRA meteorological variables. The combination of the biases for each heat flux is such that total NRA heat transfer from the ocean to the atmosphere is considerably larger than observed by KEO. These results highlight the importance of maintaining in situ observations for monitoring surface heat fluxes in the Kuroshio/Kuroshio Extension regions.
  • S. Iwasaki, M. Kubota, H. Tomita
    INTERNATIONAL JOURNAL OF REMOTE SENSING 29 21 6263 - 6280 2008年 [査読有り][通常論文]
     
    To clarify the characteristics of global sea surface temperature (SST) products, we have compared the Reynolds product with four other products: the Center for Atmospheric and Oceanic Studies (CAOS) SST, the microwave optimum interpolation (MWOI) SST, the merged satellite and in-situ data global daily (MGD) SST and the real time global (RTG) SST. Furthermore, we have validated these five products with SST data observed by moored buoys. The CAOS SST and the MWOI SST show significant underestimation in several regions. The underestimation is related to the characteristics of the original microwave data. It should be noted that the MGD SST provides the best statistics, although the high-frequency variations are removed by a low-pass filter. Moreover, we have investigated the impact of the differences between the SST products on estimated latent heat flux. In regions with strong SST gradients, the average differences are significantly large.
  • 根田 昌典, 市川 洋, 永野 憲, 富田 裕之, 時長 宏樹, 安田 一郎
    月刊海洋 49 83 - 92 海洋出版 2008年 [査読無し][通常論文]
  • 黒潮続流域における衛星データを用いた海上大気比湿の推定
    富田 裕之, 時長 宏樹, 谷本 陽一
    月刊海洋 49 93 - 99 2008年 [査読無し][通常論文]
  • Yoshimi Kawai, Toshimasa Doi, Hiroyuki Tomita, Hideharu Sasaki
    Journal of Geophysical Research 113 C8 C08021  2008年 [査読無し][通常論文]
  • Hiroyuki Tomita, Masahisa Kubota
    Journal of Geophysical Research: Oceans 111 7 2006年07月08日 [査読有り][通常論文]
     
    To analyze the accuracy of Japanese Ocean Flux data sets with Use of Remote sensing Observations (J-OFURO) latent heat flux (LHF), comparisons with moored buoy data are conducted. In the tropical region, J-OFURO LHF is characterized by large overestimations when buoy LHF has large values. On the other hand, in the midlatitudes, J-OFURO LHF tends to be underestimated when buoy LHF has large values. We have concluded that these errors are mainly caused by the accuracy of surface air specific humidity. The large scatter between satellite and buoy products is due to the low accuracy of not only specific humidity data but also wind speed data in the midlatitudes. The J-OFURO LHF bias errors are compared with the bias errors of selected satellite (GSSTF2 and HOAPS1) and reanalysis (NRA1, NRA2, ERA15 and ERA40) data sets. Copyright 2006 by the American Geophysical Union.
  • Hiroyuki Tomita, Masahisa Kubota
    JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 111 C7 2006年07月 [査読有り][通常論文]
     
    [ 1] To analyze the accuracy of Japanese Ocean Flux data sets with Use of Remote sensing Observations (J-OFURO) latent heat flux (LHF), comparisons with moored buoy data are conducted. In the tropical region, J-OFURO LHF is characterized by large overestimations when buoy LHF has large values. On the other hand, in the midlatitudes, J-OFURO LHF tends to be underestimated when buoy LHF has large values. We have concluded that these errors are mainly caused by the accuracy of surface air specific humidity. The large scatter between satellite and buoy products is due to the low accuracy of not only specific humidity data but also wind speed data in the midlatitudes. The J-OFURO LHF bias errors are compared with the bias errors of selected satellite (GSSTF2 and HOAPS1) and reanalysis (NRA1, NRA2, ERA15 and ERA40) data sets.
  • H Tomita, M Kubota
    GEOPHYSICAL RESEARCH LETTERS 32 9 2005年05月 [査読有り][通常論文]
     
    Various turbulent heat flux data indicate remarkable increase in heat loss by latent and sensible heat fluxes over Kuroshio and Kuroshio/Oyashio Extension regions during the 1990' s. This increase is found in net heat flux, and the heat flux reached its maximum during last 50 years. The slope is about 5.8 W m(-2) year(-1) on average and is found over the most part of Kuroshio, Kuroshio/Oyashio Extension regions and Japan Sea. The increase in latent heat flux dominantly contributes to the increase in turbulent heat flux mainly due to the increase in SST. Although the increase in wind speed also contributes to the increase in turbulent heat flux, the contribution is smaller than that of SST. In contrast, the increase of specific humidity which contributes the decrease in latent heat flux is also found.
  • Masahisa Kubota, Hiroyuki Tomita
    International Geoscience and Remote Sensing Symposium (IGARSS) 5 3306 - 3309 2005年 [査読有り][通常論文]
     
    We investigated the accuracy of daily-mean wind speed data observed by satellites. A satellite daily-mean value obtained by averaging the two buoy wind speed data observed at satellite observation time is compared with a true daily- mean value by averaging the all buoy data. It is shown that the accuracy strongly depends on satellite observation time. Moreover, we can remarkably improve the accuracy, if we use multiple satellites. Moreover, the usefulness of multi-satellite data for obtaining accurate wind speed data is demonstrated by comparison with buoy data. Global maps of a sampling error for each satellite data are given in the present study. © 2005 IEEE.
  • H Tomita, M Kubota
    ATMOSPHERE-OCEAN 42 3 183 - 199 2004年09月 [査読有り][通常論文]
     
    The variability of surface heat flux over the Indian Ocean is investigated using in situ observational data. First, the Indian Ocean is divided into eight regions and the power spectra of surface heat fluxes are calculated for each region. Consequently it is shown that the surface heat flux over the Indian Ocean has three characteristic timescales: (1) the high frequency timescale (periods shorter than 20 months), (2) the middle frequency timescale (periods between 20 and 60 months), and (3) the low frequency timescale (periods longer than 60 months). Seasonal variation is dominant for the high frequency timescale, with shortwave radiation and the latent heat flux being the principal components of the variability at this timescale. Furthermore, the seasonal variation can be divided into three patterns depending on the region. The variation of shortwave radiation and the latent heat flux are also dominant in the middle-frequency timescale. In some regions, heat flux variation for this timescale appears to be associated with El Nino. For the low-frequency timescale, the latent heat flux is dominant. It should be noted that the heat flux from the ocean to the atmosphere has clearly increased since the late 1970s as a result of increases in wind speeds and the specific humidity difference.
  • M Kubota, A Kano, H Muramatsu, H Tomita
    JOURNAL OF CLIMATE 16 4 670 - 678 2003年02月 [査読有り][通常論文]
     
    The Japanese Ocean Flux Data Sets with use of Remote Sensing Observations (J-OFURO) latent heat flux field is compared with the Hamburg Ocean-Atmosphere Parameters and Fluxes from Satellite Data (HOAPS), the Goddard Satellite-Based Surface Turbulent Fluxes (GSSTF), ECMWF, NCEP-NCAR reanalysis (NCEP1), and da Silva et al.'s fields. All products qualitatively reveal a similar pattern in the average fields. Although the latent heat fluxes of J-OFURO and GSSTF are quite similar, they are larger than those of HOAPS in the tropical regions. The difference between J-OFURO and the da Silva data is large, and the temporal correlation is extremely low in the Southern Hemisphere. This suggests that the da Silva product hardly reproduces accurate variability in the data-sparse regions. Also the time correlation between J-OFURO and ECMWF or NCEP1 is considerably lower in the Southern Hemisphere than in the Northern Hemisphere. The ECMWF and NCEP1 fields may be affected by the lack of ship observations there. The present study also compares meridional profiles of the zonal average. The HOAPS and da Silva products significantly underestimate these profiles in the tropical regions compared with the other products. On the other hand, the ECMWF product overestimates these profiles in the equatorial regions.
  • 根田昌典, 川口盛平, 豊田美穂, 富田裕之, 今里哲久, 久保田雅久
    月刊海洋 31 9 587 - 594 海洋出版 1999年09月01日 [査読無し][通常論文]

その他活動・業績

共同研究・競争的資金等の研究課題

  • 台風・爆弾低気圧の予測可能性とスケール間大気海洋相互作用
    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 : 2019年06月 -2024年03月 
    代表者 : 川村 隆一, 筆保 弘徳, 山本 勝, 富田 裕之, 森本 昭彦, 柳瀬 亘, 吉田 聡, 宮本 佳明
  • 大気海洋系内の熱フローの理解に立脚した地球温暖化の加速・減速の要因解明
    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 : 2018年04月 -2022年03月 
    代表者 : 谷本 陽一, 富田 裕之, 細田 滋毅, 時長 宏樹, 野中 正見, 植原 量行
     
    海洋熱吸収の10年規模変動特性と海洋熱吸収における中規模渦の役割について焦点を当てた研究を実施した。産業革命以前の実験を提供している計24モデルの出力データを整備し、 気候モデルによる海面熱フラックスの時空間変動について解析を行った。併せて、人工衛星観測に基づく海面熱フラックスの長期データとして1988年から2017年までを対象としてデータセットを再構築し、全球海洋を対象とする海面熱フラックスの長期変動の解析を開始した。その結果、 太平洋側では太平洋数十年規模振動、 大西洋側では大西洋数十年規模振動とよく似た海面水温偏差のパターンが地球温暖化の加減速に同期して現れ、 海面熱フラックスも同様に変動していることが分かった。また、これらの2つの海盆を跨ぐ熱帯海盆間変動に関連して、熱帯大西洋の自励振動が熱帯太平洋の結合変動を変調させて北太平洋の気候変動に間接的に影響することに加え、熱帯大西洋から北半球の中緯度大気循環に直接的に影響していることが示された。 さらに、海洋中規模を解像可能な海洋大循環モデルの10メンバーアンサンブル50年経年変動シミュレーション結果を用いて、本課題で注目する黒潮続流域での海洋中規模渦の変動特性と変動要因の解析を行った。僅かに異なる初期状態から同一の大気変動を与えたシミュレーションの比較から、黒潮続流域下流域では、海洋中規模渦の活動度が強く大気変動の影響を受けて変動することが示された。更に詳細な解析から、その海域での海洋中規模渦活動度の経年変動はその海域の流速の経年変動と高い相関を持ち、流速が大きいとき渦活動度が高いことが示された。また、台湾東方沖における黒潮近傍の低気圧性中規模渦の物理的特性と海洋基礎生産の関係を解析した結果、低気圧性中規模渦による低温かつ高栄養塩濃度の亜表層下部からの湧昇が、渦の相対渦度の強弱を伴うことを示した。
  • 世界最高水準の衛星海面フラックスデータが明らかにする台風と海洋の関係
    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 : 2018年04月 -2022年03月 
    代表者 : 富田 裕之, 加古 真一郎, 和田 章義, 市川 香
  • 日本学術振興会:科学研究費助成事業 基盤研究(B)
    研究期間 : 2015年04月 -2019年03月 
    代表者 : 辻野 博之, 小室 芳樹, 鈴木 立郎, 富田 裕之, 山崎 大, 浦川 昇吾, 中野 英之, 古林 慎哉, 原田 やよい, 大野木 和敏, 吉本 浩一
     
    海洋-海氷数値モデルによって海洋気候変動を可能な限り正確に再現するため、海面境界条件の算出に必要な気象変数・河川流入データセットを、気象庁大気再解析(JRA-55)に適切な修正を加えることにより作成した。本データセットを観測データや従来使用されてきたデータセットと詳細に比較検証を行った上で国際的に公開し、海洋モデル相互比較プロジェクト等、利用の促進を図った。
  • 日本学術振興会:科学研究費助成事業 基盤研究(B)
    研究期間 : 2014年04月 -2018年03月 
    代表者 : 富田 裕之, 増田 周平, 纐纈 慎也, 細田 滋毅
     
    地球規模の水循環変動のより良い理解のために、新たに開発された人工衛星淡水フラックスデータおよび改良された海洋データ同化システムで構成される統合海面淡水フラックスデータセットを整備が行われた。過去20年の淡水フラックスと表層の海洋変動との関連がこれらのデータセットを用いて研究され、全球規模の海洋変動を伴う蒸発と降水の変動が明らかになった。データセットはオープンデータのポリシーに基づき、より幅広い研究における利用のために公開された。
  • 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 : 2010年04月 -2015年03月 
    代表者 : 川合 義美, 谷本 陽一, 伊藤 進一, 富田 裕之, 岡 英太郎, 須賀 利雄, 小橋 史明, 植原 量行, 永野 憲, 小林 大洋, 榎本 剛, 黒田 寛, 立花 義裕, 根田 昌典, 井上 龍一郎, FAURE Vincent, 茂木 耕作, 谷口 京子
     
    黒潮・親潮続流域において水温前線が大気に与える影響、及び海洋前線や水塊の形成・維持過程を現場観測を基に明らかにすることを目的として、船舶による大気・海洋集中観測や係留ブイ観測を実施した。 初夏(梅雨期)の黒潮続流前線や晩冬期の亜寒帯前線が大気境界層や下層雲の高度差、下層の気圧勾配を生じさせることを示した。準定常ジェットによる亜寒帯への水塊輸送や表層栄養塩の変動を明らかにした。また、黒潮続流南側における冬季混合層の短い時間スケールでの時間発展や、サブメソスケールでの亜寒帯系水塊の南方への輸送過程を観測で捉えた。
  • 日本学術振興会:科学研究費助成事業 基盤研究(B)
    研究期間 : 2010年 -2012年 
    代表者 : 川村 隆一, 松浦 知徳, 飯塚 聡, 一柳 錦平, 富田 裕之, 楠 昌司, 水田 亮, 初鹿 宏壮, 古山 彰一
     
    大気再解析データ、衛星観測データ等の各種データ解析ならびに数値モデル(領域大気モデル、波浪予測モデル、同位体循環モデル、大気大循環モデル)を併用することで、(1) 日本周辺で発達する爆弾低気圧活動の実態の解明、(2) 爆弾低気圧活動を規定する冬季東アジアモンスーン変動と海面水温(SST)フロントの複合影響のメカニズムの解明、(3) 豪雪、局地的大雨、異常波浪をもたらす爆弾低気圧の役割の解明、(4) 将来気候における日本海側の豪雪の頻度と関連する爆弾低気圧活動の長期的変化の評価、など重要な学問的知見が得られた。また、災害軽減を目指して爆弾低気圧情報データベースを構築し整備した。
  • 日本学術振興会:科学研究費助成事業 基盤研究(C)
    研究期間 : 2010年 -2012年 
    代表者 : 細田 滋毅, 増田 周平, 川合 義美, 富田 裕之, 須賀 利雄, 長谷川 拓也, 佐藤 佳奈子
     
    全球規模の水循環変動と強い関連がある表層塩分変動過程を明らかにするために,観測的データに基づき熱帯域の表層塩分変動過程および,北太平洋域における混合層変動過程,特に暖候期における熱輸送過程について調べた.その結果,熱帯域で検出されていた塩分トレンドに含まれる準10年変動成分を定量化し,また夏季の浅い混合層から下層に浸透する熱が,大気海洋間の熱交換に大きな影響を与えることを示した.

教育活動情報

主要な担当授業

  • 現代地球惑星科学概論2
    開講年度 : 2021年
    課程区分 : 学士課程
    開講学部 : 理学部
    キーワード : 大気大循環, エネルギー収支, 地衡風, ロスビー波, 気候変動, 地球温暖化 海洋の物理現象, 地衡流、表層風成循環, 全球熱塩循環、渦、潮汐、波と乱流、北海道

大学運営

委員歴

  • 2020年 - 現在   JAXA   地球観測に関する科学アドバイザリ委員会 AMSR分科会
  • 2019年 - 2019年   JAXA   GOSAT3号機搭載用次期マイクロ波放射計ミッション要求検討委員会
  • 2012年 - 2014年   JAXA   地球圏総合委員会 海域分科会


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