研究者データベース

藤原 正智(フジワラ マサトモ)
地球環境科学研究院 地球圏科学部門 気候力学分野
教授

基本情報

所属

  • 地球環境科学研究院 地球圏科学部門 気候力学分野

職名

  • 教授

学位

  • 博士(理学)(1999年03月 東京大学)

ホームページURL

科研費研究者番号

  • 00360941

ORCID ID

Researcher ID

  • F-7852-2012

J-Global ID

研究キーワード

  • 大気科学   気象学   

研究分野

  • 自然科学一般 / 大気水圏科学

職歴

  • 2022年07月 - 現在 北海道大学 大学院地球環境科学研究院 教授
  • 2007年04月 - 2022年06月 北海道大学 大学院地球環境科学研究院・地球圏科学部門 准教授
  • 2005年04月 - 2007年03月 北海道大学 大学院地球環境科学研究院・地球圏科学部門 助教授
  • 2003年04月 - 2005年03月 北海道大学 大学院地球環境科学研究科・大気海洋圏環境科学専攻 助教授
  • 2001年04月 - 2003年03月 京都大学 宙空電波科学研究センター 日本学術振興会特別研究員PD
  • 2000年04月 - 2001年03月 北海道大学 大学院地球環境科学研究科・大気海洋圏環境科学専攻 日本学術振興会特別研究員PD
  • 1999年04月 - 2000年03月 東京大学 大学院理学系研究科・地球惑星物理学専攻 日本学術振興会特別研究員PD
  • 1998年04月 - 1999年03月 東京大学 大学院理学系研究科・地球惑星物理学専攻 日本学術振興会特別研究員DC2

学歴

  • 1996年04月 - 1999年03月   東京大学   理学系研究科   地球惑星物理学専攻 博士課程
  • 1994年04月 - 1996年03月   東京大学   理学系研究科   地球惑星物理学専攻 修士課程
  • 1990年04月 - 1994年03月   東京大学   理科I類 ~ 理学部   地球物理学科

所属学協会

  • 日本地球惑星科学連合   日本大気化学会   American Meteorological Society   日本気象学会   American Geophysical Union   

研究活動情報

論文

  • Varaha Ravi Kiran, Madineni Venkat Ratnam, Masatomo Fujiwara, Herman Russchenberg, Frank G. Wienhold, Bomidi Lakshmi Madhavan, Mekalathur Roja Raman, Renju Nandan, Sivan Thankamani Akhil Raj, Alladi Hemanth Kumar, Saginela Ravindra Babu
    Atmospheric Measurement Techniques 2022年08月19日
  • S.‐Y. Ogino, K. Miyazaki, M. Fujiwara, M. I. Nodzu, M. Shiotani, F. Hasebe, J. Matsumoto, J. Witte, A. M. Thompson, H. A. Nguyen‐Thi, T. V. Nguyen
    Journal of Geophysical Research: Atmospheres 2022年05月27日
  • Masatomo Fujiwara, Tetsu Sakai, Tomohiro Nagai, Koichi Shiraishi, Yoichi Inai, Sergey Khaykin, Haosen Xi, Takashi Shibata, Masato Shiotani, Laura L. Pan
    Atmospheric Chemistry and Physics 21 4 3073 - 3090 Copernicus GmbH 2021年03月01日 [査読有り][通常論文]
     
    Abstract. Eastward air-mass transport from the Asian summer monsoon (ASM) anticyclone in the upper troposphere and lower stratosphere (UTLS) often involves eastward-shedding vortices, which can cover most of the Japanese archipelago. We investigated the aerosol characteristics of these vortices by analysing data from two lidar systems in Japan, at Tsukuba (36.1∘ N, 140.1∘ E) and Fukuoka (33.55∘ N, 130.36∘ E), during the summer of 2018. We observed several events with enhanced particle signals at Tsukuba at 15.5–18 km of altitude (at or above the local tropopause) during August–September 2018, with a backscattering ratio of ∼ 1.10 and particle depolarization of ∼ 5 % (i.e. not spherical, but more spherical than ice crystals). These particle characteristics may be consistent with those of solid aerosol particles, such as ammonium nitrate. Each event had a timescale of a few days. During the same study period, we also observed similar enhanced particle signals in the lower stratosphere at Fukuoka. The upper troposphere is often covered by cirrus clouds at both lidar sites. Backward trajectory calculations for these sites for days with enhanced particle signals in the lower stratosphere and days without indicate that the former air masses originated within the ASM anticyclone and the latter more from edge regions. Reanalysis carbon monoxide and satellite water vapour data indicate that eastward-shedding vortices were involved in the observed aerosol enhancements. Satellite aerosol data confirm that the period and latitudinal region were free from the direct influence of documented volcanic eruptions and high-latitude forest fires. Our results indicate that the Asian tropopause aerosol layer (ATAL) over the ASM region extends east towards Japan in association with the eastward-shedding vortices and that lidar systems in Japan can detect at least the lower-stratospheric portion of the ATAL during periods when the lower stratosphere is undisturbed by volcanic eruptions and forest fires. The upper-tropospheric portion of the ATAL is either depleted by tropospheric processes (convection and wet scavenging) during eastward transport or is obscured by much stronger cirrus cloud signals.
  • Holger Vömel, Masatomo Fujiwara
    Springer Handbook of Atmospheric Measurements 1255 - 1293 2021年
  • Rolf Philipona, Andreas Kräuchi, Rigel Kivi, Thomas Peter, Martin Wild, Ruud Dirksen, Masatomo Fujiwara, Miho Sekiguchi, Dale F. Hurst, Ralf Becker
    Meteorologische Zeitschrift 29 6 501 - 509 2020年11月25日 [査読有り][通常論文]
     
    Solar shortwave and terrestrial thermal longwave irradiance are measured at radiation sites at the Earth's surface and on satellite platforms high up in space, since many years. Radiation profiles through the Earth's atmosphere, however, have only sporadically been measured from enhanced upper-air radiosondes. Here we show profiles of solar and terrestrial radiation measured with balloon-borne radiometers through cloud-free and cloudy atmospheres, which reveal radiative effects of temperature, water vapor, ozone and clouds on downward and upward radiation. Shortwave radiation profiles show solar absorption in the free atmosphere and strong reflection in clouds and albedo effects on the ground and the atmosphere above. Longwave upward radiation profiles visualize terrestrial radiation emitted from the Earth's surface, which is partly absorbed and reemitted in the boundary layer and in the atmosphere by water vapor and other greenhouse gases. Longwave downward radiation profiles show the absorbed terrestrial radiation in the atmosphere and reveal the warming effect of increasing greenhouse gases, and by this visualize and demonstrate radiative forcing and a changing greenhouse effect by water vapor in the Earth's atmosphere. Longwave net radiation profiles show terrestrial emission into space to be reduced by water vapor and clouds. Measured radiation profiles are compared to numerically calculated radiation profiles.
  • E. J. Jensen, Laura L. Pan, Shawn Honomichl, Glenn S. Diskin, Martina Krämer, Nicole Spelten, Gebhard Günther, Dale F. Hurst, Masatomo Fujiwara, Holger Vömel, Henry B. Selkirk, Junko Suzuki, Michael J. Schwartz, Jessica B. Smith
    Journal of Geophysical Research: Atmospheres 125 15 2020年08月16日 [査読有り][通常論文]
     
    In situ and remote sensing observations of water vapor are analyzed to assess the evidence for direct convective hydration of the lower stratosphere. We have examined several hundred balloon-borne and airborne in situ measurements of lower stratospheric humidity in the tropics and northern midlatitudes. We find that the tropical lower stratospheric H2O enhancements above the background occur quite infrequently, and the height of the enhancements is within about 1 km of the cold-point tropopause. Following Schwartz et al. (2013, https://doi.org/10.1002/grl.50421), we examine the anomalously high (above 8 ppmv) water vapor mixing ratios retrieved by the Aura Microwave Limb Sounder (MLS) at 100- and 82-hPa pressure levels, and we determine their vertical location relative to the local tropopause based on both Global Forecast System (GFS) operational analysis and the ERA5 reanalysis temperature data. We find that essentially all of the >8-ppmv MLS water vapor measurements over the extratropical North American monsoon region are above the relatively low lapse-rate tropopause in the region, and most are above the local cold-point tropopause. Over the Asian monsoon region, most (80/90%) of the high H2O values occur below the relatively high-altitude local lapse-rate/cold-point tropopause. Anomalously high MLS water vapor retrievals at 100 and 82 hPa almost never occur in the deep tropics. We show that this result is consistent with the in situ observations given the broad vertical averaging kernel of the MLS measurement. The available evidence suggests that direct hydration of the lower stratosphere is important over North America during the monsoon season but likely has limited impact in the tropics.
  • Yoshio Kawatani, Toshihiko Hirooka, Kevin Hamilton, Anne K. Smith, Masatomo Fujiwara
    Atmospheric Chemistry and Physics 20 14 9115 - 9133 2020年07月31日 [査読有り][通常論文]
     
    Abstract. This paper reports on a project to compare the representation of the semiannual oscillation (SAO) in the equatorial stratosphere and lower mesosphere within six major global atmospheric reanalysis datasets and with recent satellite Sounding of the Atmosphere Using Broadband Emission Radiometry (SABER) and Microwave Limb Sounder (MLS) observations. All reanalyses have a good representation of the quasi-biennial oscillation (QBO) in the equatorial lower and middle stratosphere and each displays a clear SAO centered near the stratopause. However, the differences among reanalyses are much more substantial in the SAO region than in the QBO-dominated region. The degree of disagreement among the reanalyses is characterized by the standard deviation (SD) of the monthly mean zonal wind and temperature; this depends on latitude, longitude, height, and time. The zonal wind SD displays a prominent equatorial maximum that increases with height, while the temperature SD reaches a minimum near the Equator and is largest in the polar regions. Along the Equator, the zonal wind SD is smallest around the longitude of Singapore, where consistently high-quality near-equatorial radiosonde observations are available. Interestingly, the near-Singapore minimum in SD is evident to at least ∼3 hPa, i.e., considerably higher than the usual ∼10 hPa ceiling for in situ radiosonde observations. Our measurement of the agreement among the reanalyses shows systematic improvement over the period considered (1980–2016), up to near the stratopause. Characteristics of the SAO at 1 hPa, such as its detailed time variation and the displacement off the Equator of the zonal wind SAO amplitude maximum, differ significantly among the reanalyses. Disagreement among the reanalyses becomes still greater above 1 hPa. One of the reanalyses in our study also has a version produced without assimilating satellite observations, and a comparison of the SAO in these two versions demonstrates the very great importance of satellite-derived temperatures in the realistic analysis of the tropical upper stratospheric circulation.
  • Fabio Madonna, Rigel Kivi, Jean-Charles Dupont, Bruce Ingleby, Masatomo Fujiwara, Gonzague Romanens, Miguel Hernandez, Xavier Calbet, Marco Rosoldi, Aldo Giunta, Tomi Karppinen, Masami Iwabuchi, Shunsuke Hoshino, Christoph von Rohden, Peter William Thorne
    Atmospheric Measurement Techniques 13 7 3621 - 3649 2020年07月08日 [査読有り][通常論文]
     
    Abstract. In the last two decades, technological progress has not only seen improvements to the quality of atmospheric upper-air observations but also provided the opportunity to design and implement automated systems able to replace measurement procedures typically performed manually. Radiosoundings, which remain one of the primary data sources for weather and climate applications, are still largely performed around the world manually, although increasingly fully automated upper-air observations are used, from urban areas to the remotest locations, which minimize operating costs and challenges in performing radiosounding launches. This analysis presents a first step to demonstrating the reliability of the automatic radiosonde launchers (ARLs) provided by Vaisala, Meteomodem and Meisei. The metadata and datasets collected by a few existing ARLs operated by the Global Climate Observing System (GCOS) Reference Upper-Air Network (GRUAN) certified or candidate sites (Sodankylä, Payerne, Trappes, Potenza) have been investigated and a comparative analysis of the technical performance (i.e. manual versus ARL) is reported. The performance of ARLs is evaluated as being similar or superior to those achieved with the traditional manual launches in terms of percentage of successful launches, balloon burst and ascent speed. For both temperature and relative humidity, the ground-check comparisons showed a negative bias of a few tenths of a degree and % RH, respectively. Two datasets of parallel soundings between manual and ARL-based measurements, using identical sonde models, provided by Sodankylä and Faa'a stations, showed mean differences between the ARL and manual launches smaller than ±0.2 K up to 10 hPa for the temperature profiles. For relative humidity, differences were smaller than 1 % RH for the Sodankylä dataset up to 300 hPa, while they were smaller than 0.7 % RH for Faa'a station. Finally, the observation-minus-background (O–B) mean and root mean square (rms) statistics for German RS92 and RS41 stations, which operate a mix of manual and ARL launch protocols, calculated using the European Centre for Medium-Range Weather Forecasts (ECMWF) forecast model, are very similar, although RS41 shows larger rms(O–B) differences for ARL stations, in particular for temperature and wind. A discussion of the potential next steps proposed by GRUAN community and other parties is provided, with the aim to lay the basis for the elaboration of a strategy to fully demonstrate the value of ARLs and guarantee that the provided products are traceable and suitable for the creation of GRUAN data products.
  • Masatomo Fujiwara, Patrick Martineau, Jonathon S. Wright
    Atmospheric Chemistry and Physics 20 1 345 - 374 2020年01月10日 [査読有り][通常論文]
     
    Abstract. The global response of air temperature at 2 m above the surface to the eruptions of Mount Agung in March 1963, El Chichón in April 1982, and Mount Pinatubo in June 1991 is investigated using 11 global atmospheric reanalysis data sets (JRA-55, JRA-25, MERRA-2, MERRA, ERA-Interim, ERA-40, CFSR, NCEP-NCAR R-1, 20CR version 2c, ERA-20C, and CERA-20C). Multiple linear regression (MLR) is applied to the monthly mean time series of temperature for two periods – 1980–2010 (for 10 reanalyses) and 1958–2001 (for 6 reanalyses) – by considering explanatory factors of seasonal harmonics, linear trends, quasi-biennial oscillation (QBO), solar cycle, tropical sea surface temperature (SST) variations in the Pacific, Indian, and Atlantic Oceans, and Arctic SST variations. Empirical orthogonal function (EOF) analysis is applied to these climatic indices to obtain a set of orthogonal indices to be used for the MLR. The residuals of the MLR are used to define the volcanic signals for the three eruptions separately. First, area-averaged time series of the residuals are investigated and compared with the results from previous studies. Then, the geographical distribution of the response during the peak cooling period after each eruption is investigated. In general, different reanalyses show similar geographical patterns of the response, but with the largest differences in the polar regions. The Pinatubo response shows the largest average cooling in the 60∘ N–60∘ S region among the three eruptions, with a peak cooling of 0.10–0.15 K. The El Chichón response shows slightly larger cooling in the NH than in the Southern Hemisphere (SH), while the Agung response shows larger cooling in the SH. These hemispheric differences are consistent with the distribution of stratospheric aerosol optical depth after these eruptions; however, the peak cooling after these two eruptions is comparable in magnitude to unexplained cooling events in other periods without volcanic influence. Other methods in which the MLR model is used with different sets of indices are also tested, and it is found that careful treatment of tropical SST variability is necessary to evaluate the surface response to volcanic eruptions in observations and reanalyses.
  • Suginori Iwasaki, Takafumi Seguchi, Hajime Okamoto, Kaori Sato, Shuichiro Katagiri, Masatomo Fujiwara, Takashi Shibata, Kazuhisa Tsuboki, Takashi Ono, Takuji Sugidachi
    Polar Science 21 117 - 123 2019年09月 [査読有り][通常論文]
     
    Large-and-Sparse-particle Clouds (LSC), characterized by large particle size (radius > 50 μm) and small number concentration (<104 m−3), were observed with the space-borne lidar, Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), and with the space-borne 94-GHz cloud profiling radar (CPR). CALIOP was found to be less sensitive to the LSC as compared to CPR because of the particle size distribution of LSC; hence, the cloud type is different from usual ones because CALIOP is generally more sensitive to clouds as compared to CPR when there is no lidar attenuation. An empirical criterion was introduced to identify the LSC from CALIOP and CPR data. The data analysis showed that the LSC tend to appear at high latitudes. The lifetime of LSC would be in the order of hours, because the terminal velocity of LSC particles exceeded 1 km h−1. LSC would not be fallstreak because no cloud existed above. LSC appeared to destroy supercooled clouds (SC) because their cloud top heights were higher as compared to SC, and because LSC and SC did not tend to coexist. Because of their thin optical depth, LSC did not directly impact radiative forcing; however, LSC may indirectly influence radiative forcing through changes in the distribution of SC.
  • Young-Ha Kim, George N. Kiladis, John R. Albers, Juliana Dias, Masatomo Fujiwara, James A. Anstey, In-Sun Song, Corwin J. Wright, Yoshio Kawatani, François Lott, Changhyun Yoo
    Atmospheric Chemistry and Physics 19 15 10027 - 10050 2019年08月09日 [査読有り][通常論文]
     
    Abstract. Equatorial Kelvin and mixed Rossby–gravity (MRG) waves in the tropical tropopause layer and stratosphere represented in recent reanalyses for the period of 1981–2010 are compared in terms of spectral characteristics, spatial structures, long-term variations, and their forcing of the quasi-biennial oscillation (QBO). For both wave types, the spectral distributions are broadly similar among most of the reanalyses, while the peak amplitudes exhibit considerable spread. The longitudinal distributions and spatial patterns of wave perturbations show reasonable agreement between the reanalyses. A few exceptions to the similarity of the spectral shapes and spatial structures among them are also noted. While the interannual variations of wave activity appear to be coherent for both the Kelvin and MRG waves, there is substantial variability in long-term trends among the reanalyses. Most of the reanalyses which assimilate satellite data exhibit large increasing trends in wave variance (∼15 %–50 % increase in 30 years at 100–10 hPa), whereas one reanalysis (Japanese 55-year Reanalysis assimilating conventional observations only; JRA-55C) produced without satellite data does not. Several discontinuities are found around 1998 in the time series of the Kelvin and MRG wave variances, which manifest in different ways depending on the reanalysis, and are indicative of impacts of the transition of satellite measurements during that year. The equatorial wave forcing of the QBO, estimated by the Eliassen–Palm (EP) flux divergence, occurs in similar phase-speed ranges in the lower stratosphere among the reanalyses. However, the EP flux and its divergence are found to be dependent on the zonal-mean winds represented in reanalyses, exhibiting different magnitudes, altitudes, and phase-speed ranges of the Kelvin wave forcing between the reanalyses, especially at 20–10 hPa. In addition, at around 20 hPa, a wave signal which appears only in easterly mean winds with westward phase speeds is found and discussed.
  • Eriko Kobayashi, Shunsuke Hoshino, Masami Iwabuchi, Takuji Sugidachi, Kensaku Shimizu, Masatomo Fujiwara
    Atmospheric Measurement Techniques 12 6 3039 - 3065 2019年06月04日 [査読有り][通常論文]
     
    Abstract. A total of 87 dual flights of Meisei RS-11G radiosondes and Vaisala RS92-SGP radiosondes were carried out at the Aerological Observatory of the Japan Meteorological Agency (36.06∘ N, 140.13∘ E, 25.2 m) from April 2015 to June 2017. Global Climate Observing System (GCOS) Reference Upper-Air Network (GRUAN) data products from both sets of radiosonde data for 52 flights were subsequently created using a documented processing program along with the provision of optimal estimates for measurement uncertainty. Differences in the performance of the radiosondes were then quantified using the GRUAN data products. The temperature measurements of RS-11G were, on average, 0.4 K lower than those of RS92-SGP in the stratosphere for daytime observations. The relative humidity measurements of RS-11G were, on average, 2 % RH (relative humidity) lower than those of RS92-SGP under 90 % RH–100 % RH conditions, while RS-11G gave on average 5 % RH higher values than RS92-SGP under ≤50 % RH conditions. The results from a dual flight of RS-11G and a cryogenic frost point hygrometer (CFH) also showed that RS-11G gave 1 % RH–10 % RH higher values than the CFH in the troposphere. Differences between the RS-11G and RS92-SGP temperature and relative humidity measurements, based on combined uncertainties, were also investigated to clarify major influences behind the differences. It was found that temperature differences in the stratosphere during daytime observation were within the range of uncertainty (k=2), and that sensor orientation is the major source of uncertainty in the RS92-SGP temperature measurement, while sensor albedo is the major source of uncertainty for RS-11G. The relative humidity difference in the troposphere was larger than the uncertainty (k=2) after the radiosondes had passed through the cloud layer, and the temperature–humidity dependence correction was the major source of uncertainty in RS-11G relative humidity measurement. Uncertainties for all soundings were also statistically investigated. Most nighttime temperature measurements for pressures of >10 hPa were in agreement, while relative humidity in the middle troposphere exhibited significant differences. Around half of all daytime temperature measurements at pressures of ≤150 hPa and relative humidity measurements around the 500 hPa level were not in agreement.
  • Noersomadi, Toshitaka Tsuda, Masatomo Fujiwara
    Atmospheric Chemistry and Physics 19 10 6985 - 7000 2019年05月24日 [査読有り][通常論文]
     
    Abstract. Using COSMIC GPS Radio Occultation (RO) observations from January 2007 to December 2016, we retrieved temperature profiles with the height resolution of about 0.1 km in the upper troposphere and lower stratosphere (UTLS). We investigated the distribution of static stability (N2) and the zonal structure of the tropopause inversion layer (TIL) in the tropics, where a large change in the temperature gradient occurs associated with sharp variations in N2. We show the variations in the mean N2 profiles in coordinates relative to the cold-point tropopause (CPT). A very thin (<1 km) layer is found with average maximum N2 in the range of 11.0–12.0×10-4 s−2. The mean and standard deviation of TIL sharpness, defined as the difference between the maximum N2 (max⁡N2) and minimum N2 (min⁡N2) within ±1 km of the CPT, is (10.5±3.7)×10-4 s−2. The max⁡N2 is typically located within 0.5 km above CPT. We focused on the variation in TIL sharpness in two longitude regions, 90–150∘ E (Maritime Continent; MC) and 170–230∘ E (Pacific Ocean; PO), with different land–sea distribution. Seasonal variations in TIL sharpness and thickness were related to the deep convective activity represented by low outgoing longwave radiation (OLR) during the Australian and Asian monsoons. The deviation from the mean sharpness (sharpness anomaly) was out of phase with the OLR anomaly in both the MC and PO. The correlation between the sharpness anomaly over the MC and PO and the sea surface temperature (SST) Niño 3.4 index was −0.66 and +0.88, respectively. During La Niña (SST Niño 3.4 <-0.5 K) in the MC and El Niño (SST Niño 3.4 >+0.5 K) in the PO, warmer SSTs in the MC and PO produce more active deep convection that tends to force the air upward to the tropopause layer and increase the temperature gradient there. The intraseasonal variation in sharpness anomaly during slow and fast episodes of the Madden–Julian Oscillation (MJO) demonstrates that eastward propagation of the positive sharpness anomaly is associated with organized deep convection. Deep convection during MJO will tend to decrease N2 below CPT and increase N2 above CPT, thus enlarging the TIL sharpness. Convective activity in the tropics is a major control on variations in tropopause sharpness at intraseasonal to interannual timescales.
  • Rolf Philipona, Carl Mears, Masatomo Fujiwara, Pierre Jeannet, Peter Thorne, Greg Bodeker, Leopold Haimberger, Maxime Hervo, Christoph Popp, Gonzague Romanens, Wolfgang Steinbrecht, Rene Stübi, Roeland Van Malderen
    Journal of Geophysical Research: Atmospheres 123 22 2018年11月27日 [査読有り][通常論文]
     
    Since the mid-twentieth century, radiosonde and satellite measurements show that the troposphere has warmed and the stratosphere has cooled. These changes are primarily due to increasing concentrations of well-mixed greenhouse gases and the depletion of stratospheric ozone. In response to continued greenhouse gas increases and stratospheric ozone depletion, climate models project continued tropospheric warming and stratospheric cooling over the coming decades. Global average satellite observations of lower stratospheric temperatures exhibit no significant trends since the turn of the century. In contrast, an analysis of vertically resolved radiosonde measurements from 60 stations shows an increase of lower stratospheric temperature since the turn of the century at altitudes between 15 and 30 km and over most continents. Trend estimates are somewhat sensitive to homogeneity assessment choices, but all investigated radiosonde data sets suggest a change from late twentieth century cooling to early 21st century warming in the lower stratosphere, which is consistent with a reversal from ozone depletion to recovery from the effects of ozone-depleting substances. In comparison, satellite observations at the radiosonde locations show only minor early 21st century warming, possibly due to the compensating effects of continued cooling above the radiosonde altitude range.
  • Patrick Martineau, Jonathon S. Wright, Nuanliang Zhu, Masatomo Fujiwara
    Earth System Science Data 10 4 1925 - 1941 2018年10月18日 [査読有り][通常論文]
     
    Abstract. This data set, which is prepared for the Stratosphere–troposphere Processes And their Role in Climate (SPARC) Reanalysis Intercomparison Project (S-RIP), provides several zonal-mean diagnostics computed from reanalysis data on pressure levels. Diagnostics are currently provided for a variety of reanalyses, including ERA-40, ERA-Interim, ERA-20C, NCEP–NCAR, NCEP–DOE, CFSR, 20CR v2 and v2c, JRA-25, JRA-55, JRA-55C, JRA-55AMIP, MERRA, and MERRA-2. The data set will be expanded to include additional reanalyses as they become available. Basic dynamical variables (such as temperature, geopotential height, and three-dimensional winds) are provided in addition to a complete set of terms from the Eulerian-mean and transformed-Eulerian-mean momentum equations. Total diabatic heating and its long-wave and shortwave components are included as availability permits, along with heating rates diagnosed from the basic dynamical variables using the zonal-mean thermodynamic equation. Two versions of the data set are provided, one that uses horizontal and vertical grids provided by the various reanalysis centers and another that uses a common grid (CG) to facilitate comparison among data sets. For the common grid, all diagnostics are interpolated horizontally onto a regular 2.5∘×2.5∘ grid for a subset of pressure levels that are common among all included reanalyses. The dynamical (Martineau, 2017, https://doi.org/10.5285/b241a7f536a244749662360bd7839312) and diabatic (Wright, 2017, https://doi.org/10.5285/70146c789eda4296a3c3ab6706931d56) variables are archived and maintained by the Centre for Environmental Data Analysis (CEDA).
  • Yoichi Inai, Shuji Aoki, Hideyuki Honda, Hiroshi Furutani, Yutaka Matsumi, Mai Ouchi, Satoshi Sugawara, Fumio Hasebe, Mitsuo Uematsu, Masatomo Fujiwara
    Atmospheric Environment 184 24 - 36 2018年07月 [査読有り][通常論文]
     
    Vertical profiles of carbon dioxide (CO2) mixing ratio in the equatorial eastern and western Pacific were measured by newly developed balloon-borne CO2 sondes in February 2012 (two soundings) and February–March 2015 (four soundings), respectively. The 1–10 km vertically averaged CO2 mixing ratios lie between the background surface values in the Northern Hemisphere (NH) and those in the Southern Hemisphere (SH) monitored at ground-based sites during these periods. A backward trajectory analysis, taking account of convective mixing processes using geostationary satellite cloud-image data, is applied to the measured CO2 profiles to estimate the origin of the observed air masses. Air masses originating in the SH show low CO2 mixing ratios that are similar to the background values in the SH. This relationship is confirmed by a positive correlation (∼0.6) between the CO2 mixing ratio and the latitude of air mass origin which is found from trajectory calculations. This result suggests that the CO2 distribution in the troposphere over the equatorial Pacific is controlled by monthly time-scale, large-scale CO2 distribution and weekly time-scale atmospheric transport processes. Furthermore, this study shows that the combination of CO2 sonde measurements and trajectory analysis, taking account of convective mixing, is a useful tool in investigating CO2 transport processes.
  • F. Hasebe, S. Aoki, S. Morimoto, Y. Inai, T. Nakazawa, S. Sugawara, C. Ikeda, H. Honda, H. Yamazaki, Halimurrahman, N. Komala, F. A. Putri, A. Budiyono, M. Soedjarwo, S. Ishidoya, S. Toyoda, T. Shibata, M. Hayashi, N. Eguchi, N. Nishi, M. Fujiwara, S.-Y. Ogino, M. Shiotani, T. Sugidachi
    Bulletin of the American Meteorological Society 99 6 1213 - 1230 2018年06月 [査読有り][通常論文]
     
    AbstractThe stratospheric response to climate forcing, such as an increase in greenhouse gases, is often unpredictable because of interactions between radiation, dynamics, and chemistry. Climate models are unsuccessful in simulating the realistic distribution of stratospheric water vapor. The long-term trend of the stratospheric age of air (AoA), a measure that characterizes the stratospheric turnover time, remains inconsistent between diagnoses in climate models and estimates from tracer observations. For these reasons, observations designed specifically to distinguish the effects of individual contributing processes are required. Here, we report on the Coordinated Upper-Troposphere-to-Stratosphere Balloon Experiment in Biak (CUBE/Biak), an observation campaign organized in Indonesia. Being inside the “tropical pipe” makes it possible to study the dehydration in the tropical tropopause layer and the gradual ascent in the stratosphere while minimizing the effects of multiple circulation pathways and wave mixing. Cryogenic sampling of minor constituents and major isotopes was conducted simultaneously with radiosonde observations of water vapor, ozone, aerosols, and cloud particles. The water vapor “tape recorder,” gravitational separation, and isotopocules are being studied in conjunction with tracers that are accumulated in the atmosphere as dynamical and chemical measures of elapsed time since stratospheric air entry. The observational estimates concerning the AoA and water vapor tape recorder are compared with those derived from trajectory calculations.
  • Takatoshi Sakazaki, Masatomo Fujiwara, Masato Shiotani
    Atmospheric Chemistry and Physics 18 2 1437 - 1456 2018年02月01日 [査読有り][通常論文]
     
    Abstract. Atmospheric solar tides in the stratosphere and the lower mesosphere are investigated using temperature data from five state-of-the-art reanalysis data sets (MERRA-2, MERRA, JRA-55, ERA-Interim, and CFSR) as well as TIMED SABER and Aura MLS satellite measurements. The main focus is on the period 2006–2012 during which the satellite observations are available for direct comparison with the reanalyses. Diurnal migrating tides, semidiurnal migrating tides, and nonmigrating tides are diagnosed. Overall the reanalyses agree reasonably well with each other and with the satellite observations for both migrating and nonmigrating components, including their vertical structure and the seasonality. However, the agreement among reanalyses is more pronounced in the lower stratosphere and relatively weaker in the upper stratosphere and mesosphere. A systematic difference between SABER and the reanalyses is found for diurnal migrating tides in the upper stratosphere and the lower mesosphere; specifically, the amplitude of trapped modes in reanalyses is significantly smaller than that in SABER, although such difference is less clear between MLS and the reanalyses. The interannual variability and the possibility of long-term changes in migrating tides are also examined using the reanalyses during 1980–2012. All the reanalyses agree in exhibiting a clear quasi-biennial oscillation (QBO) in the tides, but the most significant indications of long-term changes in the tides represented in the reanalyses are most plausibly explained by the evolution of the satellite observing systems during this period. The tides are also compared in the full reanalyses produced by the Japan Meteorological Agency (i.e., JRA-55) and in two parallel data sets from this agency: one (JRA-55C) that repeats the reanalysis procedure but without any satellite data assimilated and one (JRA-55AMIP) that is a free-running integration of the model constrained only by observed sea surface temperatures. Many aspects of the tides are closer in JRA-55C and JRA-55AMIP than these are to the full reanalysis JRA-55, demonstrating the importance of the assimilation of satellite data in representing the diurnal variability of the middle atmosphere. In contrast to the assimilated data sets, the free-running model has no QBO in equatorial stratospheric mean circulation and our results show that it displays no quasi-biennial variability in the tides.
  • Anne M. Thompson, Jacquelyn C. Witte, Chance Sterling, Allen Jordan, Bryan J. Johnson, Samuel J. Oltmans, Masatomo Fujiwara, Holger Vömel, Marc Allaart, Ankie Piters, Gert J. R. Coetzee, Françoise Posny, Ernesto Corrales, Jorge Andres Diaz, Christian Félix, Ninong Komala, Nga Lai, H. T. Ahn Nguyen, Matakite Maata, Francis Mani, Zamuna Zainal, Shin‐ya Ogino, Francisco Paredes, Tercio Luiz Bezerra Penha, Francisco Raimundo Silva, Sukarni Sallons‐Mitro, Henry B. Selkirk, F. J. Schmidlin, Rene Stübi, Kennedy Thiongo
    Journal of Geophysical Research: Atmospheres 122 23 2017年12月16日 [査読有り][通常論文]
     
    The Southern Hemisphere ADditional OZonesonde (SHADOZ) network was assembled to validate a new generation of ozone-monitoring satellites and to better characterize the vertical structure of tropical ozone in the troposphere and stratosphere. Beginning with nine stations in 1998, more than 7,000 ozone and P-T-U profiles are available from 14 SHADOZ sites that have operated continuously for at least a decade. We analyze ozone profiles from the recently reprocessed SHADOZ data set that is based on adjustments for inconsistencies caused by varying ozonesonde instruments and operating techniques. First, sonde-derived total ozone column amounts are compared to the overpasses from the Earth Probe/Total Ozone Mapping Spectrometer, Ozone Monitoring Instrument, and Ozone Mapping and Profiler Suite satellites that cover 1998–2016. Second, characteristics of the stratospheric and tropospheric columns are examined along with ozone structure in the tropical tropopause layer (TTL). We find that (1) relative to our earlier evaluations of SHADOZ data, in 2003, 2007, and 2012, sonde-satellite total ozone column offsets at 12 stations are 2% or less, a significant improvement; (2) as in prior studies, the 10 tropical SHADOZ stations, defined as within ±19° latitude, display statistically uniform stratospheric column ozone, 229 ± 3.9 DU (Dobson units), and a tropospheric zonal wave-one pattern with a 14 DU mean amplitude; (3) the TTL ozone column, which is also zonally uniform, masks complex vertical structure, and this argues against using satellites for lower stratospheric ozone trends; and (4) reprocessing has led to more uniform stratospheric column amounts across sites and reduced bias in stratospheric profiles. As a consequence, the uncertainty in total column ozone now averages 5%.
  • Craig S. Long, Masatomo Fujiwara, Sean Davis, Daniel M. Mitchell, Corwin J. Wright
    Atmospheric Chemistry and Physics 17 23 14593 - 14629 Copernicus {GmbH} 2017年12月07日 [査読有り][通常論文]
     
    Abstract. Two of the most basic parameters generated from a reanalysis are temperature and winds. Temperatures in the reanalyses are derived from conventional (surface and balloon), aircraft, and satellite observations. Winds are observed by conventional systems, cloud tracked, and derived from height fields, which are in turn derived from the vertical temperature structure. In this paper we evaluate as part of the SPARC Reanalysis Intercomparison Project (S-RIP) the temperature and wind structure of all the recent and past reanalyses. This evaluation is mainly among the reanalyses themselves, but comparisons against independent observations, such as HIRDLS and COSMIC temperatures, are also presented. This evaluation uses monthly mean and 2.5° zonal mean data sets and spans the satellite era from 1979–2014. There is very good agreement in temperature seasonally and latitudinally among the more recent reanalyses (CFSR, MERRA, ERA-Interim, JRA-55, and MERRA-2) between the surface and 10 hPa. At lower pressures there is increased variance among these reanalyses that changes with season and latitude. This variance also changes during the time span of these reanalyses with greater variance during the TOVS period (1979–1998) and less variance afterward in the ATOVS period (1999–2014). There is a distinct change in the temperature structure in the middle and upper stratosphere during this transition from TOVS to ATOVS systems. Zonal winds are in greater agreement than temperatures and this agreement extends to lower pressures than the temperatures. Older reanalyses (NCEP/NCAR, NCEP/DOE, ERA-40, JRA-25) have larger temperature and zonal wind disagreement from the more recent reanalyses. All reanalyses to date have issues analysing the quasi-biennial oscillation (QBO) winds. Comparisons with Singapore QBO winds show disagreement in the amplitude of the westerly and easterly anomalies. The disagreement with Singapore winds improves with the transition from TOVS to ATOVS observations. Temperature bias characteristics determined via comparisons with a reanalysis ensemble mean (MERRA, ERA-Interim, JRA-55) are similarly observed when compared with Aura HIRDLS and Aura MLS observations. There is good agreement among the NOAA TLS, SSU1, and SSU2 Climate Data Records and layer mean temperatures from the more recent reanalyses. Caution is advised for using reanalysis temperatures for trend detection and anomalies from a long climatology period as the quality and character of reanalyses may have changed over time.
  • Sean M. Davis, Michaela I. Hegglin, Masatomo Fujiwara, Rossana Dragani, Yayoi Harada, Chiaki Kobayashi, Craig Long, Gloria L. Manney, Eric R. Nash, Gerald L. Potter, Susann Tegtmeier, Tao Wang, Krzysztof Wargan, Jonathon S. Wright
    Atmospheric Chemistry and Physics 17 20 12743 - 12778 2017年10月26日 [査読有り][通常論文]
     
    Abstract. Reanalysis data sets are widely used to understand atmospheric processes and past variability, and are often used to stand in as "observations" for comparisons with climate model output. Because of the central role of water vapor (WV) and ozone (O3) in climate change, it is important to understand how accurately and consistently these species are represented in existing global reanalyses. In this paper, we present the results of WV and O3 intercomparisons that have been performed as part of the SPARC (Stratosphere–troposphere Processes and their Role in Climate) Reanalysis Intercomparison Project (S-RIP). The comparisons cover a range of timescales and evaluate both inter-reanalysis and observation-reanalysis differences. We also provide a systematic documentation of the treatment of WV and O3 in current reanalyses to aid future research and guide the interpretation of differences amongst reanalysis fields.The assimilation of total column ozone (TCO) observations in newer reanalyses results in realistic representations of TCO in reanalyses except when data coverage is lacking, such as during polar night. The vertical distribution of ozone is also relatively well represented in the stratosphere in reanalyses, particularly given the relatively weak constraints on ozone vertical structure provided by most assimilated observations and the simplistic representations of ozone photochemical processes in most of the reanalysis forecast models. However, significant biases in the vertical distribution of ozone are found in the upper troposphere and lower stratosphere in all reanalyses.In contrast to O3, reanalysis estimates of stratospheric WV are not directly constrained by assimilated data. Observations of atmospheric humidity are typically used only in the troposphere, below a specified vertical level at or near the tropopause. The fidelity of reanalysis stratospheric WV products is therefore mainly dependent on the reanalyses' representation of the physical drivers that influence stratospheric WV, such as temperatures in the tropical tropopause layer, methane oxidation, and the stratospheric overturning circulation. The lack of assimilated observations and known deficiencies in the representation of stratospheric transport in reanalyses result in much poorer agreement amongst observational and reanalysis estimates of stratospheric WV. Hence, stratospheric WV products from the current generation of reanalyses should generally not be used in scientific studies.
  • Guanyu Huang, Xiong Liu, Kelly Chance, Kai Yang, Pawan K. Bhartia, Zhaonan Cai, Marc Allaart, Gérard Ancellet, Bertrand Calpini, Gerrie J, R. Coetzee, Emilio Cuevas-Agulló, Manuel Cupeiro, Hugo De Backer, Manvendra K. Dubey, Henry E. Fuelberg, Masatomo Fujiwara, Sophie Godin-Beekmann, Tristan J. Hall, Bryan Johnson, Everette Joseph, Rigel Kivi, Bogumil Kois, Ninong Komala, Gert König-Langlo, Giovanni Laneve, Thierry Leblanc, Marion Marchand, Kenneth R. Minschwaner, Gary Morris, Michael J. Newchurch, Shin-Ya Ogino, Nozomu Ohkawara, Ankie J. M. Piters, Françoise Posny, Richard Querel, Rinus Scheele, Frank J. Schmidlin, Russell C. Schnell, Otto Schrems, Henry Selkirk, Masato Shiotani, Pavla Skrivánková, René Stübi, Ghassan Taha, David W. Tarasick, Anne M. Thompson, Valérie Thouret, Matthew B. Tully, Roeland Van Malderen, Holger Vömel, Peter von der Gathen, Jacquelyn C. Witte, Margarita Yela
    Atmospheric Measurement Techniques 10 7 2455 - 2475 European Geosciences Union (EGU) 2017年07月13日 [査読有り][通常論文]
     
    We validate the Ozone Monitoring Instrument (OMI) Ozone Profile (PROFOZ) product from October 2004 through December 2014 retrieved by the Smithsonian Astrophysical Observatory (SAO) algorithm against ozonesonde observations. We also evaluate the effects of OMI row anomaly (RA) on the retrieval by dividing the dataset into before and after the occurrence of serious OMI RA, i.e., pre-RA (2004–2008) and post-RA (2009–2014). The retrieval shows good agreement with ozonesondes in the tropics and midlatitudes and for pressure  < ∼ 50 hPa in the high latitudes. It demonstrates clear improvement over the a priori down to the lower troposphere in the tropics and down to an average of ∼ 550 (300) hPa at middle (high) latitudes. In the tropics and midlatitudes, the profile mean biases (MBs) are less than 6 %, and the standard deviations (SDs) range from 5 to 10 % for pressure  < ∼ 50 hPa to less than 18 % (27 %) in the tropics (midlatitudes) for pressure  > ∼ 50 hPa after applying OMI averaging kernels to ozonesonde data. The MBs of the stratospheric ozone column (SOC, the ozone column from the tropopause pressure to the ozonesonde burst pressure) are within 2 % with SDs of  < 5 % and the MBs of the tropospheric ozone column (TOC) are within 6 % with SDs of 15 %. In the high latitudes, the profile MBs are within 10 % with SDs of 5–15 % for pressure  < ∼ 50 hPa but increase to 30 % with SDs as great as 40 % for pressure  > ∼ 50 hPa. The SOC MBs increase up to 3 % with SDs as great as 6 % and the TOC SDs increase up to 30 %. The comparison generally degrades at larger solar zenith angles (SZA) due to weaker signals and additional sources of error, leading to worse performance at high latitudes and during the midlatitude winter. Agreement also degrades with increasing cloudiness for pressure  > ∼ 100 hPa and varies with cross-track position, especially with large MBs and SDs at extreme off-nadir positions. In the tropics and midlatitudes, the post-RA comparison is considerably worse with larger SDs reaching 2 % in the stratosphere and 8 % in the troposphere and up to 6 % in TOC. There are systematic differences that vary with latitude compared to the pre-RA comparison. The retrieval comparison demonstrates good long-term stability during the pre-RA period but exhibits a statistically significant trend of 0.14–0.7 % year[−1] for pressure  < ∼ 80 hPa, 0.7 DU year[−1] in SOC, and −0. 33 DU year[−1] in TOC during the post-RA period. The spatiotemporal variation of retrieval performance suggests the need to improve OMI's radiometric calibration especially during the post-RA period to maintain the long-term stability and reduce the latitude/season/SZA and cross-track dependency of retrieval quality.
  • Masahiro Sugiyama, Shinichiro Asayama, Atsushi Ishii, Takanobu Kosugi, John C. Moore, Jolene Lin, Penehuro F. Lefale, Wil Burns, Masatomo Fujiwara, Arunabha Ghosh, Joshua Horton, Atsushi Kurosawa, Andy Parker, Michael Thompson, Pak-Hang Wong, Lili Xia
    Climatic Change 143 1-2 1 - 12 2017年07月 [査読有り][通常論文]
     
    Increasing interest in climate engineering in recent years has led to calls by the international research community for international research collaboration as well as global public engagement. But making such collaboration a reality is challenging. Here, we report the summary of a 2016 workshop on the significance and challenges of international collaboration on climate engineering research with a focus on the Asia-Pacific region. Because of the region’s interest in benefits and risks of climate engineering, there is a potential synergy between impact research on anthropogenic global warming and that on solar radiation management. Local researchers in the region can help make progress toward better understanding of impacts of solar radiation management. These activities can be guided by an ad hoc Asia-Pacific working group on climate engineering, a voluntary expert network. The working group can foster regional conversations in a sustained manner while contributing to capacity building. An important theme in the regional conversation is to develop effective practices of dialogues in light of local backgrounds such as cultural traditions and past experiences of large-scale technology development. Our recommendation merely portrays one of several possible ways forward, and it is our hope to stimulate the debate in the region.
  • Jacquelyn C. Witte, Anne M. Thompson, Herman G. J. Smit, Masatomo Fujiwara, Françoise Posny, Gert J. R. Coetzee, Edward T. Northam, Bryan J. Johnson, Chance W. Sterling, Maznorizan Mohamad, Shin-Ya Ogino, Allen Jordan, Francisco R, da Silva
    Journal of Geophysical Research: Atmospheres 122 12 6611 - 6636 2017年06月27日 [査読有り][通常論文]
     
    Electrochemical concentration cell ozonesonde measurements are an important source of highly resolved vertical profiles of ozone (O3) with long-term data records for deriving O3 trends, model development, satellite validation, and air quality studies. Ozonesonde stations employ a range of operational and data processing procedures, metadata reporting, and instrument changes that have resulted in inhomogeneities within individual station data records. A major milestone is the first reprocessing of seven Southern Hemisphere ADditional OZonesondes (SHADOZ) station ozonesonde records to account for errors and biases in operating/processing procedures. Ascension Island, Hanoi, Irene, Kuala Lumpur, La Réunion, Natal, and Watukosek station records all show an overall increase in O3 after reprocessing. Watukosek shows the largest increase of 9.0 ± 2.1 Dobson Units (DU) in total column O3; Irene and Hanoi show a 5.5 ± 2.5 DU increase, while remaining sites show statistically insignificant enhancements. Negligible to modest O3 enhancements are observed after reprocessing in the troposphere (up to 8%) and stratosphere (up to 6%), except at La Réunion for which the application of background currents reduces tropospheric O3 (−2.1 ± 1.3 DU). Inhomogeneities due to ozonesonde/solution-type changes at Ascension, Natal, and La Réunion are resolved with the application of transfer functions. Comparisons with EP-TOMS, Aura's Ozone Monitoring Instrument and Microwave Limb Sounder (MLS) satellite O3 overpasses show an overall improvement in agreement after reprocessing. Most reprocessed data sets show a significant reduction in biases with MLS at the ozone maximum region (50–10 hPa). Changes in radiosonde/ozonesonde system and nonstandard solution types can account for remaining discrepancies observed at several sites when compared to satellites.
  • Masatomo Fujiwara, Jonathon S. Wright, Gloria L. Manney, Lesley J. Gray, James Anstey, Thomas Birner, Sean Davis, Edwin P. Gerber, V. Lynn Harvey, Michaela I. Hegglin, Cameron R. Homeyer, John A. Knox, Kirstin Krüger, Alyn Lambert, Craig S. Long, Patrick Martineau, Andrea Molod, Beatriz M. Monge-Sanz, Michelle L. Santee, Susann Tegtmeier, Simon Chabrillat, David G. H. Tan, David R. Jackson, Saroja Polavarapu, Gilbert P. Compo, Rossana Dragani, Wesley Ebisuzaki, Yayoi Harada, Chiaki Kobayashi, Will McCarty, Kazutoshi Onogi, Steven Pawson, Adrian Simmons, Krzysztof Wargan, Jeffrey S. Whitaker, Cheng-Zhi Zou
    Atmospheric Chemistry and Physics 17 2 1417 - 1452 Copernicus {GmbH} 2017年01月31日 [査読有り][通常論文]
     
    Abstract. The climate research community uses atmospheric reanalysis data sets to understand a wide range of processes and variability in the atmosphere, yet different reanalyses may give very different results for the same diagnostics. The Stratosphere–troposphere Processes And their Role in Climate (SPARC) Reanalysis Intercomparison Project (S-RIP) is a coordinated activity to compare reanalysis data sets using a variety of key diagnostics. The objectives of this project are to identify differences among reanalyses and understand their underlying causes, to provide guidance on appropriate usage of various reanalysis products in scientific studies, particularly those of relevance to SPARC, and to contribute to future improvements in the reanalysis products by establishing collaborative links between reanalysis centres and data users. The project focuses predominantly on differences among reanalyses, although studies that include operational analyses and studies comparing reanalyses with observations are also included when appropriate. The emphasis is on diagnostics of the upper troposphere, stratosphere, and lower mesosphere. This paper summarizes the motivation and goals of the S-RIP activity and extensively reviews key technical aspects of the reanalysis data sets that are the focus of this activity. The special issue The SPARC Reanalysis Intercomparison Project (S-RIP) in this journal serves to collect research with relevance to the S-RIP in preparation for the publication of the planned two (interim and full) S-RIP reports.
  • Masahiro Sugiyama, Shinichiro Asayama, Takanobu Kosugi, Atsushi Ishii, Seita Emori, Jiro Adachi, Keigo Akimoto, Masatomo Fujiwara, Tomoko Hasegawa, Yasushi Hibi, Kimiko Hirata, Toru Ishii, Takeshi Kaburagi, Yuki Kita, Shigeki Kobayashi, Atsushi Kurosawa, Manabu Kuwata, Kooiti Masuda, Makoto Mitsui, Taku Miyata, Hiroshi Mizutani, Sumie Nakayama, Kazuyo Oyamada, Takaaki Sashida, Miho Sekiguchi, Kiyoshi Takahashi, Yukari Takamura, Junichi Taki, Taketoshi Taniguchi, Hiroyuki Tezuka, Takahiro Ueno, Shingo Watanabe, Rie Watanabe, Naoyuki Yamagishi, Go Yoshizawa
    Sustainability Science 12 1 31 - 44 [Integrated Research System for Sustainability Science] [編] 2017年01月 [査読有り][通常論文]
     
    Interest in climate engineering research has grown rapidly owing to the slow progress of international climate negotiations. As some scientists are proposing to expand research and conduct field tests, there is an emerging debate about whether and how it should proceed. It is widely accepted both by the supporters and critics that public engagement from the early stage of research is necessary. Nonetheless, most, if not all, of existing research projects of climate engineering were designed predominantly by experts. To produce socially relevant knowledge, and hence, pursue transdisciplinary research that integrates interdisciplinary research and public engagement, it is desirable for scientists to decide together with the public on what kind of research should be done. In this paper, we both as Japanese scientists and stakeholders collaboratively identify 40 socially relevant research questions on climate engineering with a particular emphasis on stratospheric aerosol injection, using a method designed to encourage science–policy collaboration. While we acknowledge some methodological problems and the difficulty in obtaining active participation from stakeholders, the list of identified questions covers broad interdisciplinary perspectives and diverse interests, and may provide an important foundation for future transdisciplinary research on climate engineering. Given the dynamic nature of climate change and policy responses, research agendas should be periodically and iteratively reviewed and updated through transdisciplinary processes.
  • Masatomo Fujiwara, Takuji Sugidachi, Toru Arai, Kensaku Shimizu, Mayumi Hayashi, Yasuhisa Noma, Hideaki Kawagita, Kazuo Sagara, Taro Nakagawa, Satoshi Okumura, Yoichi Inai, Takashi Shibata, Suginori Iwasaki, Atsushi Shimizu
    Atmospheric Measurement Techniques 9 12 5911 - 5931 2016年12月09日 [査読有り][通常論文]
     
    Abstract. A meteorological balloon-borne cloud sensor called the cloud particle sensor (CPS) has been developed. The CPS is equipped with a diode laser at  ∼  790 nm and two photodetectors, with a polarization plate in front of one of the detectors, to count the number of particles per second and to obtain the cloud-phase information (i.e. liquid, ice, or mixed). The lower detection limit for particle size was evaluated in laboratory experiments as  ∼  2 µm diameter for water droplets. For the current model the output voltage often saturates for water droplets with diameter equal to or greater than  ∼  80 µm. The upper limit of the directly measured particle number concentration is  ∼  2 cm−3 (2 × 103 L−1), which is determined by the volume of the detection area of the instrument. In a cloud layer with a number concentration higher than this value, particle signal overlap and multiple scattering of light occur within the detection area, resulting in a counting loss, though a partial correction may be possible using the particle signal width data. The CPS is currently interfaced with either a Meisei RS-06G radiosonde or a Meisei RS-11G radiosonde that measures vertical profiles of temperature, relative humidity, height, pressure, and horizontal winds. Twenty-five test flights have been made between 2012 and 2015 at midlatitude and tropical sites. In this paper, results from four flights are discussed in detail. A simultaneous flight of two CPSs with different instrumental configurations confirmed the robustness of the technique. At a midlatitude site, a profile containing, from low to high altitude, water clouds, mixed-phase clouds, and ice clouds was successfully obtained. In the tropics, vertically thick cloud layers in the middle to upper troposphere and vertically thin cirrus layers in the upper troposphere were successfully detected in two separate flights. The data quality is much better at night, dusk, and dawn than during the daytime because strong sunlight affects the measurements of scattered light.
  • Hiroyasu Kubokawa, Masaki Satoh, Junko Suzuki, Masatomo Fujiwara
    Journal of Geophysical Research: Atmospheres 121 19 11556 - 11574 2016年10月16日 [査読有り][通常論文]
     
    Temperature variations in the tropical tropopause layer (TTL) play an important role in dehydration in the upper troposphere and lower stratosphere. Equatorial Kelvin waves associated with the Madden-Julian Oscillation (MJO) are known to induce remarkable temperature variations in the TTL. In this study, the influence of topography on temperature variations in the TTL is investigated by using radiosonde data, satellite data, reanalysis data, and numerically simulated data. When MJO convection passes over the radiosonde sites, temperature variations near mountainous regions are larger than those measured in regions of lower elevation. The difference in temperature amplitude reaches ~1–2 K. Large temperature variations over mountainous regions were also found in other data sets. Numerically simulated data from the Nonhydrostatic Icosahedral Atmospheric Model (NICAM) are also used to investigate the temperature variations in the TTL. The results show that the temperature variations associated with Kelvin waves become large over mountainous regions. A sensitivity test using the stretched version of NICAM gave two important results: (i) the height of mountains affects the magnitude of the temperature variations in the TTL, and (ii) the terrain-following coordinate system used in the model produces the artificially high-temperature variation in the TTL. When Kelvin waves pass over mountainous regions, topographic gravity waves are excited and superimposed on the Kelvin waves, thereby producing large temperature variations over these regions. The mountainous region of the Indonesian Maritime Continent is a favorable location for large temperature variations in the TTL.
  • Sean M. Davis, Karen H. Rosenlof, Birgit Hassler, Dale F. Hurst, William G. Read, Holger Vömel, Henry Selkirk, Masatomo Fujiwara, Robert Damadeo
    Earth System Science Data 8 2 461 - 490 Copernicus Publications on behalf of the European Geosciences Union (EGU) 2016年09月28日 [査読有り][通常論文]
     
    In this paper, we describe the construction of the Stratospheric Water and Ozone Satellite Homogenized(SWOOSH) database, which includes vertically resolved ozone and water vapor data from a subset of thelimb profiling satellite instruments operating since the 1980s. The primary SWOOSH products are zonal-meanmonthly-mean time series of water vapor and ozone mixing ratio on pressure levels (12 levels per decade from316 to 1 hPa). The SWOOSH pressure level products are provided on several independent zonal-mean grids (2.5,5, and 10 ), and additional products include two coarse 3-D griddings (30 long 10 lat, 20 5 ) as well asa zonal-mean isentropic product. SWOOSH includes both individual satellite source data as well as a mergeddata product. A key aspect of the merged product is that the source records are homogenized to account forinter-satellite biases and to minimize artificial jumps in the record. We describe the SWOOSH homogenizationprocess, which involves adjusting the satellite data records to a "reference" satellite using coincident observationsduring time periods of instrument overlap. The reference satellite is chosen based on the best agreementwith independent balloon-based sounding measurements, with the goal of producing a long-term data record thatis both homogeneous (i.e., with minimal artificial jumps in time) and accurate (i.e., unbiased). This paper detailsthe choice of reference measurements, homogenization, and gridding process involved in the construction of thecombined SWOOSH product and also presents the ancillary information stored in SWOOSH that can be used infuture studies of water vapor and ozone variability. Furthermore, a discussion of uncertainties in the combinedSWOOSH record is presented, and examples of the SWOOSH record are provided to illustrate its use for studiesof ozone and water vapor variability on interannual to decadal timescales. The version 2.5 SWOOSH data arepublicly available at doi:10.7289/V5TD9VBX.
  • Yoshio Kawatani, Kevin Hamilton, Kazuyuki Miyazaki, Masatomo Fujiwara, James A. Anstey
    Atmospheric Chemistry and Physics 16 11 6681 - 6699 2016年 [査読有り][通常論文]
     
    This paper reports on a project to compare the representation of the monthly-mean zonal wind in the equatorial stratosphere among major global atmospheric reanalysis data sets. The degree of disagreement among the reanalyses is characterized by the standard deviation (SD) of the monthly-mean zonal wind and this depends on latitude, longitude, height, and the phase of the quasi-biennial oscillation (QBO). At each height the SD displays a prominent equatorial maximum, indicating the particularly challenging nature of the reanalysis problem in the low-latitude stratosphere. At 50-70aEuro-hPa the geographical distributions of SD are closely related to the density of radiosonde observations. The largest SD values are over the central Pacific, where few in situ observations are available. At 10-20aEuro-hPa the spread among the reanalyses and differences with in situ observations both depend significantly on the QBO phase. Notably the easterly-to-westerly phase transitions in all the reanalyses except MERRA are delayed relative to those directly observed in Singapore. In addition, the timing of the easterly-to-westerly phase transitions displays considerable variability among the different reanalyses and this spread is much larger than for the timing of the westerly-to-easterly phase changes. The eddy component in the monthly-mean zonal wind near the Equator is dominated by zonal wavenumber 1 and 2 quasi-stationary planetary waves propagating from midlatitudes in the westerly phase of the QBO. There generally is considerable disagreement among the reanalyses in the details of the quasi-stationary waves near the Equator. At each level, there is a tendency for the agreement to be best near the longitude of Singapore, suggesting that the Singapore observations act as a strong constraint on all the reanalyses. Our measures of the quality of the reanalysis clearly show systematic improvement over the period considered (1979-2012). The SD among the reanalysis declines significantly over the record, although the geographical pattern of SD remains nearly constant.
  • D. M. Mitchell, L. J. Gray, M. Fujiwara, T. Hibino, J. A. Anstey, W. Ebisuzaki, Y. Harada, C. Long, S. Misios, P. A. Stott, D. Tan
    QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY 141 691 2011 - 2031 2015年07月 [査読有り][通常論文]
     
    A multiple linear regression analysis of nine different reanalysis datasets has been performed to test the robustness of variability associated with volcanic eruptions, the El Nino Southern Oscillation, the Quasi-Biennial Oscillation and with a specific focus on the 11-year solar cycle. The analysis covers both the stratosphere and troposphere and extends over the period 1979-2009. The characteristic signals of all four sources of variability are remarkably consistent between the datasets and confirm the responses seen in previous analyses. In general, the solar signatures reported are primarily due to the assimilation of observations, rather than the underlying forecast model used in the reanalysis system. Analysis of the 11-year solar response in the lower stratosphere confirms the existence of the equatorial temperature maximum, although there is less consistency in the upper stratosphere, probably reflecting the reduced level of assimilated data there. The solar modulation of the polar jet oscillation is also evident, but only significant during February. In the troposphere, vertically banded anomalies in zonal mean zonal winds are seen in all the reanalyses, with easterly anomalies at 30 degrees N and 30 degrees S suggesting a weaker and possibly broader Hadley circulation under solar maximum conditions. This structure is present in the annual signal and is particularly evident in NH wintertime. As well as the top-down' solar contribution to Northern Annular Mode variability, we show the potential contribution from the surface conditions allowing for a bottom-up' pathway. Finally, the reanalyses are compared with both observed global-mean temperatures from the Stratospheric Sounding Unit (SSU) and from the latest general circulation models from CMIP-5. The SSU samples the stratosphere over three different altitudes, and the 11-year solar cycle fingerprint is identified in these observations using detection and attribution techniques.
  • Sanjay Kumar Mehta, Masatomo Fujiwara, Toshitaka Tsuda, Jean-Paul Vernier
    JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS 129 99 - 110 2015年07月 [査読有り][通常論文]
     
    The impact of the recent minor volcanic eruptions during 2001-2010 in the temperature of the upper troposphere and lower stratosphere (UTLS) is investigated using data from the Global Positioning System Radio Occultation (GPS RO), three radiosonde compilations and two reanalyses (ERA-Interim and MERRA). The volcanic signals are identified in the residual temperature time series after removal of the linear trend, the quasi-biennial oscillation and El Nino Southern Oscillation components. Eight minor volcanic eruptions (six from the tropics and two from midlatitude) over the last decade (2001-2010) are analyzed in this study. We found significant volcanic signals in the UTLS temperature only in association with the tropical Soufriere Hills and Tavurvur eruptions (in May 2006 and in October 2006, respectively). Other four tropical eruptions had very small aerosol perturbations and did not show any significant UTLS temperature change. Out of the two midlatitude eruptions, Sarychev peak had similar stratospheric aerosol perturbations as Soufriere Hills and Tavurvur eruptions, but did not show any significant UTLS temperature change. The volcanic signals in the UTLS temperature from the tropical Soufriere Hills and Tavurvur eruptions were observed for the period of 7 months after August 2006. A warming of 0.5-0.8 K in the tropical 16-18.5 km (100-70 hPa) layer was observed in association with these two tropical eruptions. (c) 2015 Elsevier Ltd. All rights reserved.
  • M. Fujiwara, T. Hibino, S. K. Mehta, L. Gray, D. Mitchell, J. Anstey
    ATMOSPHERIC CHEMISTRY AND PHYSICS 15 23 13507 - 13518 2015年 [査読有り][通常論文]
     
    The global temperature responses to the eruptions of Mount Agung in 1963, El Chichon in 1982, and Mount Pinatubo in 1991 are investigated using nine currently available reanalysis data sets (JRA-55, MERRA, ERA-Interim, NCEP-CFSR, JRA-25, ERA-40, NCEP-1, NCEP-2, and 20CR). Multiple linear regression is applied to the zonal and monthly mean time series of temperature for two periods, 1979-2009 (for eight reanalysis data sets) and 19582001 (for four reanalysis data sets), by considering explanatory factors of seasonal harmonics, linear trends, Quasi-Biennial Oscillation, solar cycle, and El Nino Southern Oscillation. The residuals are used to define the volcanic signals for the three eruptions separately, and common and different responses among the older and newer reanalysis data sets are highlighted for each eruption. In response to the Mount Pinatubo eruption, most reanalysis data sets show strong warming signals (up to 2-3K for 1-year average) in the tropical lower stratosphere and weak cooling signals (down to - 1 K) in the subtropical upper troposphere. For the El Chichon eruption, warming signals in the tropical lower stratosphere are somewhat smaller than those for the Mount Pinatubo eruption. The response to the Mount Agung eruption is asymmetric about the equator with strong warming in the Southern Hemisphere midlatitude upper troposphere to lower stratosphere. Comparison of the results from several different reanalysis data sets confirms the atmospheric temperature response to these major eruptions qualitatively, but also shows quantitative differences even among the most recent reanalysis data sets. The consistencies and differences among different reanalysis data sets provide a measure of the confidence and uncertainty in our current understanding of the volcanic response. The results of this intercomparison study may be useful for validation of climate model responses to volcanic forcing and for assessing proposed geo-engineering by stratospheric aerosol injection, as well as to link studies using only a single reanalysis data set to other studies using a different reanalysis data set.
  • Y. Inai, M. Shiotani, M. Fujiwara, F. Hasebe, H. Voemel
    Atmospheric Measurement Techniques 8 10 4043 - 4054 2015年 [査読有り][通常論文]
     
    Previous research has found that conventional radiosondes equipped with a traditional pressure sensor can be subject to a pressure bias, particularly in the stratosphere. This study examines this pressure bias and the resulting altitude misestimation, and its impact on temperature, ozone, and water vapor profiles is considered using data obtained between December 2003 and January 2010 during the Soundings of Ozone and Water in the Equatorial Region (SOWER) campaigns. The payload consisted of a radiosonde (Vaisala RS80), ozone and water vapor sondes, and a global positioning system (GPS) sensor. More than 30 soundings are used in this study. As GPS height data are thought to be highly accurate, they can be used to calculate pressure. The RS80 pressure bias in the tropical stratosphere is estimated to be - 0.4 +/- 0.2 hPa (1 sigma) between 20 and 30 km. As this pressure bias is negative throughout the stratosphere, it leads to systematic overestimation of geopotential height by 43 +/- 23, 110 +/- 40, and 240 +/- 92m (1 sigma) at 20, 25, and 30 km, respectively when it is calculated by using the hypsometric equation. Because of the altitude overestimation, we see some offsets in observation parameters having a vertical gradient such as temperature, ozone, and water vapor. Those offsets in the meteorological soundings obtained using the RS80 may have generated an artificial trend in the meteorological records when radiosondes were changed from the RS80, which had no GPS unit, to the new ones with a GPS unit. Therefore, it is important to take those offsets into account in climate change studies.
  • Suzuki Junko, Fujiwara Masatomo, Nishizawa Tomoaki, Shirooka Ryuichi, Yoneyama Kunio, Katsumata Masaki, Matsui Ichiro, Sugimoto Nobuo
    Journal of Geophysical Research: Atmospheres 118 23 12 - 12 American Geophysical Union 2013年12月16日
  • Junko Suzuki, Masatomo Fujiwara, Tomoaki Nishizawa, Ryuichi Shirooka, Kunio Yoneyama, Masaki Katsumata, Ichiro Matsui, Nobuo Sugimoto
    Journal of Geophysical Research Atmospheres 118 23 12941 - 12947 2013年12月16日 [査読有り][通常論文]
     
    Cirrus cloud variability associated with n = 0 eastward inertio-gravity equatorial waves and equatorial Kelvin waves (both with the period of ~4 days) and equatorial Kelvin wave with another periodicity (~16 days) were observed in the tropical Indian Ocean (8.0°S, 80.5°E) in November of 2011 during the Cooperative Indian Ocean experiment on intraseasonal variability in the Year 2011 (CINDY2011)/Dynamics of the Madden-Julian Oscillation (DYNAMO) field campaign using balloon-borne cryogenic frostpoint hygrometers, Vaisala radiosondes, and a shipborne high spectral resolution lidar system. During early to mid-November, the cirrus cloud appearance corresponded primarily with high supersaturation and high relative humidity caused by the temperature disturbances associated with the ~4 day waves between 12 km altitude and the cold-point tropopause. The cirrus clouds disappeared under the unfavorable (downward wind and dry) conditions that were caused by the ~4 day waves, although the ~16 day wave was generating favorable conditions. Our multi-instrument cirrus measurements revealed that we must consider the phases of various overlapping waves when estimating dehydration efficiency caused by cirrus clouds around the cold-point tropopause. Key Points TTL cirrus clouds were observed over the tropical Indian Ocean Short-period equatorial waves affected the TTL cirrus clouds Wave overlapping is important for the dehydration ©2013. American Geophysical Union. All Rights Reserved.
  • T. Sakazaki, M. Fujiwara, X. Zhang
    JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS 105 66 - 80 2013年12月 [査読有り][通常論文]
     
    The latitudinal-vertical structure and the seasonal variation of the diurnal migrating tide (DW1) from the troposphere to the lower mesosphere are investigated, using reanalysis data from the Modern Era Retrospective analysis for Research and Applications (MERRA) and a linear tidal model. For the latitudinal-vertical structure, the observed feature is well represented by the four lowest-order classical Hough modes each of which shows its own unique vertical propagation characteristics. The tropospheric profile of DW1 temperature in the tropics is found to be mainly controlled by the first symmetric propagating Hough mode. The constant phase in the troposphere is due to the small static stability in the troposphere. For the seasonal variation, the amplitude from the stratosphere to the lower mesosphere maximizes at solstices. This is caused by a major contribution from the anti-symmetric propagating Hough mode. It is found that this seasonal variation is not explained by that of diabatic heating. Using a linear model, we found that background zonal wind is important for the seasonality. Also, using a modified mode-coupling approach, we interpret that in addition to primary tides generated by diabatic heating, secondary tides generated by meridional advection of background zonal momentum have a large contribution to the DW1, creating the above-mentioned seasonal variation from the stratosphere to the lower mesosphere in the tropics. It is suggested that both excitation and propagation characteristics can be physically interpreted in terms of the superposition of independent classical Hough modes. That is, each Hough mode is not only primarily excited by diabatic heating but also secondarily by mechanical forcing, and then propagates by following its own vertical propagation characteristics. (C) 2013 Elsevier Ltd. All rights reserved.
  • Koji Imai, Masatomo Fujiwara, Yoichi Inai, Naohiro Manago, Makoto Suzuki, Takuki Sano, Chihiro Mitsuda, Yoko Naito, Fumio Hasebe, Takashi Koide, Masato Shiotani
    Journal of Geophysical Research Atmospheres 118 22 12755 - 12765 2013年11月27日 [査読有り][通常論文]
     
    We compared ozone profiles measured by the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) with those taken at worldwide ozonesonde stations. To assess the quality of the SMILES version 2.3 ozone data for 16-30 km, 601 ozonesonde profiles were compared with the coincident SMILES ozone profiles. The agreement between SMILES and ozonesonde measurements was generally good within 5%-7% for 18-30 km at middle and high latitudes but degraded below 18 km. At low latitudes, however, the SMILES ozone data showed larger values (∼6%-15% for 20-26 km) than those at middle and high latitudes. To explain this bias, we explored some possible issues in the ozonesonde measurement system. One possibility is due to a pressure bias in radiosonde measurements with a pressure sensor, but it would be within a few percent. We also examined an issue of the ozonesonde's response time. The response time was estimated from ozonesonde measurements with ascending and descending profiles showing clear difference, by using the time lag correction method to minimize the difference between them. Our estimation shows 28 s on average which is a similar value derived by prelaunch preparation. By applying this correction to the original profiles, we found a negative bias of the ascending ozonesonde measurement more than 7% at 20 km in the equatorial latitude where the vertical gradient of ozone is steep. The corrected ozonesonde profiles showed better agreement with the SMILES data. We suggest that the response time of ozonesondes could create a negative bias, particularly in the lower stratosphere at equatorial latitudes. Key Points SMILES ozone profiles are compared with worldwide ozonesondes This study presents the quality of the SMILES ozone product Suggest a possible bias of ozonesonde measurements ©2013. American Geophysical Union. All Rights Reserved.
  • Koji Imai, Naohiro Manago, Chihiro Mitsuda, Yoko Naito, Eriko Nishimoto, Takatoshi Sakazaki, Masatomo Fujiwara, Lucien Froidevaux, Thomas Von Clarmann, Gabriele P. Stiller, Donal P. Murtagh, Ping-Ping Rong, Martin G. Mlynczak, Kaley A. Walker, Douglas E. Kinnison, Hideharu Akiyoshi, Tetsu Nakamura, Takayuki Miyasaka, Toshiyuki Nishibori, Satoko Mizobuchi, Ken-Ichi Kikuchi, Hiroyuki Ozeki, Chikako Takahashi, Hiroo Hayashi, Takuki Sano, Makoto Suzuki, Masahiro Takayanagi, Masato Shiotani
    Journal of Geophysical Research Atmospheres 118 11 5750 - 5769 2013年06月16日 [査読有り][通常論文]
     
    The Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) onboard the International Space Station provided global measurements of ozone profiles in the middle atmosphere from 12 October 2009 to 21 April 2010. We present validation studies of the SMILES version 2.1 ozone product based on coincidence statistics with satellite observations and outputs of chemistry and transport models (CTMs). Comparisons of the stratospheric ozone with correlative data show agreements that are generally within 10%. In the mesosphere, the agreement is also good and better than 30% even at a high altitude of 73 km, and the SMILES measurements with their local time coverage also capture the diurnal variability very well. The recommended altitude range for scientific use is from 16 to 73 km. We note that the SMILES ozone values for altitude above 26 km are smaller than some of the correlative satellite datasets conversely the SMILES values in the lower stratosphere tend to be larger than correlative data, particularly in the tropics, with less than 8% difference below ∼24 km. The larger values in the lower stratosphere are probably due to departure of retrieval results between two detection bands at altitudes below 28 km it is ∼3% at 24 km and is increasing rapidly down below. © 2013. American Geophysical Union. All Rights Reserved.
  • Takuji Sugidachi, Masatomo Fujiwara
    JOURNAL OF THE METEOROLOGICAL SOCIETY OF JAPAN 91 3 323 - 336 2013年06月 [査読有り][通常論文]
     
    Comparisons of relative humidity (RH) measurements between the Meisei RS-06G radiosonde and a chilled-mirror hygrometer revealed that the RS-06G radiosonde shows a stepwise change of similar to 3% RH at 0 degrees C (drying when air temperature is decreasing). This is due to a discontinuous correction factor in the processing software that compensates for the temperature dependence of the RH sensor. Results from chamber experiments regarding the temperature and RH dependence of RS-06G RH sensors under steady-state conditions showed a wet bias exceeding 7% RH below similar to+10 degrees C. As this result contradicted previous in-flight intercomparisons that used the original manufacturer's correction, we investigated a possible additional dry bias caused by a thermal lag in the RH sensor. We speculated that the thermal lag of the RH sensor typically causes a dry bias during a tropospheric ascent, which largely compensates for the wet bias related to the temperature and RH dependence of the RH sensor. We observed that the experimental results of the temperature and RH dependence considering the thermal lag were in agreement with the extrapolation of the original manufacturer's correction. Consequently, we proposed to extrapolate the original manufacturer's correction, which is currently applied at temperatures between -40 degrees C and 0 degrees C, up to +14.5 degrees C to resolve the artificial stepwise change at 0 degrees C. Because the RS-06G radiosonde is a successor to the Meisei RS-01G and RS2-91 radiosondes, which have adopted the same RH sensor material installed since July 1999 and have used the same processing software, the current results should be applied to the data obtained by those radiosondes. The bias of RS-06G RH measurements using this new correction is estimated to be within 7% RH, which is within the manufacturer's specifications, being drier at +40 degrees C and wetter between -40 degrees C and +10 degrees C.
  • S. Y. Ogino, M. Fujiwara, M. Shiotani, F. Hasebe, J. Matsumoto, Thuy Ha T. Hoang, Tan Thanh T. Nguyen
    Journal of Geophysical Research Atmospheres 118 8 3245 - 3257 2013年04月27日 [査読有り][通常論文]
     
    Seasonal and subseasonal variations in the ozone mixing ratio (OMR) are investigated by using continuous 7 year ozonesonde data from Hanoi (21°N, 106°E), Vietnam. The mean seasonal variations for the 7 years show large amplitude at the upper troposphere and lower stratosphere (UTLS) region (10-18 km) and at the lower troposphere (around 3 km) with standard deviations normalized by the annual mean value of about 30% for both regions. In the UTLS region, the seasonal variation in the OMR shows a minimum in winter and a maximum in spring to summer. The variation seems to be caused by the seasonal change in horizontal transport. Low OMR air masses are transported from the equatorial troposphere in winter by the anticyclonic flow associated with the equatorial convections, and high OMR air masses are transported from the midlatitude stratosphere in summer possibly due to Rossby wave breakings in the UT region and anticyclonic circulation associated with the Tibetan High in the LS region. In the lower troposphere, a spring maximum is found at 3 km height. Biomass burning and tropopause foldings are suggested as possible causes of this maximum. Subseasonal variations in the OMR show large amplitude in the UTLS region (at around 15 km) and in the boundary layer (below 1 km) with the standard deviations normalized by the annual mean larger than 40%. The OMR variations in the winter UTLS region have a negative correlation with the meridional wind. This relation indicates that the low OMRs observed at Hanoi has been transported from the equatorial region. ©2013. American Geophysical Union. All Rights Reserved.
  • Takatoshi Sakazaki, Masatomo Fujiwara, Chihiro Mitsuda, Koji Imai, Naohiro Manago, Yoko Naito, Tetsu Nakamura, Hideharu Akiyoshi, Douglas Kinnison, Takuki Sano, Makoto Suzuki, Masato Shiotani
    Journal of Geophysical Research Atmospheres 118 7 2991 - 3006 2013年04月16日 [査読有り][通常論文]
     
    Considerable uncertainties remain in the global pattern of diurnal variation in stratospheric ozone, particularly lower to middle stratospheric ozone, which is the principal contributor to total column ozone. The Superconducting Submillimeter-Wave Limb- Emission Sounder (SMILES) attached to the Japanese Experiment Module (JEM) on board the International Space Station (ISS) was developed to gather high-quality global measurements of stratospheric ozone at various local times, with the aid of superconducting mixers cooled to 4K by a compact mechanical cooler. Using the SMILES dataset, as well as data from nudged chemistry-climate models (MIROC3.2-CTM and SD-WACCM), we show that the SMILES observational data have revealed the global pattern of diurnal ozone variations throughout the stratosphere. We also found that these variations can be explained by both photochemistry and dynamics. The peak-to-peak difference in the stratospheric ozone mixing ratio (total column ozone) reached 8% (1%) over the course of a day. This variation needs to be considered when merging ozone data from different satellite measurements and even from measurements made using one specific instrument at different local times. © 2013. American Geophysical Union. All Rights Reserved.
  • S. -Y. Ogino, M. Fujiwara, M. Shiotani, F. Hasebe, J. Matsumoto, Thuy Ha T. Hoang, Tan Thanh T. Nguyen
    JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 118 8 3245 - 3257 2013年04月 [査読有り][通常論文]
     
    Seasonal and subseasonal variations in the ozone mixing ratio (OMR) are investigated by using continuous 7 year ozonesonde data from Hanoi (21 degrees N, 106 degrees E), Vietnam. The mean seasonal variations for the 7 years show large amplitude at the upper troposphere and lower stratosphere (UTLS) region (10-18 km) and at the lower troposphere (around 3 km) with standard deviations normalized by the annual mean value of about 30% for both regions. In the UTLS region, the seasonal variation in the OMR shows a minimum in winter and a maximum in spring to summer. The variation seems to be caused by the seasonal change in horizontal transport. Low OMR air masses are transported from the equatorial troposphere in winter by the anticyclonic flow associated with the equatorial convections, and high OMR air masses are transported from the midlatitude stratosphere in summer possibly due to Rossby wave breakings in the UT region and anticyclonic circulation associated with the Tibetan High in the LS region. In the lower troposphere, a spring maximum is found at 3 km height. Biomass burning and tropopause foldings are suggested as possible causes of this maximum. Subseasonal variations in the OMR show large amplitude in the UTLS region (at around 15 km) and in the boundary layer (below 1 km) with the standard deviations normalized by the annual mean larger than 40%. The OMR variations in the winter UTLS region have a negative correlation with the meridional wind. This relation indicates that the low OMRs observed at Hanoi has been transported from the equatorial region.
  • Y. Kasai, H. Sagawa, D. Kreyling, E. Dupuy, P. Baron, J. Mendrok, K. Suzuki, T. O. Sato, T. Nishibori, S. Mizobuchi, K. Kikuchi, T. Manabe, H. Ozeki, T. Sugita, M. Fujiwara, Y. Irimajiri, K. A. Walker, P. F. Bernath, C. Boone, G. Stiller, T. von Clarmann, J. Orphal, J. Urban, D. Murtagh, E. J. Llewellyn, D. Degenstein, A. E. Bourassa, N. D. Lloyd, L. Froidevaux, M. Birk, G. Wagner, F. Schreier, J. Xu, P. Vogt, T. Trautmann, M. Yasui
    ATMOSPHERIC MEASUREMENT TECHNIQUES 6 9 2311 - 2338 2013年 [査読有り][通常論文]
     
    We observed ozone (O-3) in the vertical region between 250 and 0.0005 hPa (similar to 12-96 km) using the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) on the Japanese Experiment Module (JEM) of the International Space Station (ISS) between 12 October 2009 and 21 April 2010. The new 4K superconducting heterodyne receiver technology of SMILES allowed us to obtain a one order of magnitude better signal-to-noise ratio for the O-3 line observation compared to past spaceborne microwave instruments. The non-sun-synchronous orbit of the ISS allowed us to observe O-3 at various local times. We assessed the quality of the vertical profiles of O-3 in the 100-0.001 hPa (similar to 16-90 km) region for the SMILES NICT Level 2 product version 2.1.5. The evaluation is based on four components: error analysis; internal comparisons of observations targeting three different instrumental setups for the same O-3 625.371 GHz transition; internal comparisons of two different retrieval algorithms; and external comparisons for various local times with ozonesonde, satellite and balloon observations (ENVISAT/MIPAS, SCISAT/ACE-FTS, Odin/OSIRIS, Odin/SMR, Aura/MLS, TELIS). SMILES O-3 data have an estimated absolute accuracy of better than 0.3 ppmv (3%) with a vertical resolution of 3-4 km over the 60 to 8 hPa range. The random error for a single measurement is better than the estimated systematic error, being less than 1, 2, and 7%, in the 40-1, 80-0.1, and 100-0.004 hPa pressure regions, respectively. SMILES O-3 abundance was 10-20% lower than all other satellite measurements at 8-0.1 hPa due to an error arising from uncertainties of the tangent point information and the gain calibration for the intensity of the spectrum. SMILES O-3 from observation frequency Band-B had better accuracy than that from Band-A. A two month period is required to accumulate measurements covering 24 h in local time of O-3 profile. However such a dataset can also contain variation due to dynamical, seasonal, and latitudinal effects.
  • Takuji Sugidachi, Masatomo Fujiwara
    Scientific Online Letters on the Atmosphere 9 1 179 - 182 2013年 [査読有り][通常論文]
     
    A new temperature-dependence correction (T-D correction) for Meisei RS2-91, RS-01G, and RS-06G radiosonde relative humidity (RH) measurements has been developed recently to remove the artificial stepwise change of ~3% RH at 0°C associated with the present (original) correction. These radiosondes have been used at most of the Japanese upper-air stations since the 1990s. The historical radiosonde humidity records at Sapporo and Tateno stations on the 925, 700, and 500 hPa pressure levels show apparent large downward trends between 1999 and 2009. This is because the original T-D correction has only been applied since February 2003 after a moist bias was discovered. The new T-D correction is found to result in a much smaller downward RH trend at Sapporo and almost no trend at Tateno.
  • F. Hasebe, Y. Inai, M. Shiotani, M. Fujiwara, H. Voemel, N. Nishi, S. -Y. Ogino, T. Shibata, S. Iwasaki, N. Komala, T. Peter, S. J. Oltmans
    ATMOSPHERIC CHEMISTRY AND PHYSICS 13 8 4393 - 4411 2013年 [査読有り][通常論文]
     
    A network of balloon-borne radiosonde observations employing chilled-mirror hygrometers for water and electrochemical concentration cells for ozone has been operated since the late 1990s in the Tropical Pacific to capture the evolution of dehydration of air parcels advected quasi-horizontally in the Tropical Tropopause Layer (TTL). The analysis of this dataset is made on isentropes taking advantage of the conservative properties of tracers moving adiabatically. The existence of ice particles is diagnosed by lidars simultaneously operated with sonde flights. Characteristics of the TTL dehydration are presented on the basis of individual soundings and statistical features. Supersaturations close to 80% in relative humidity with respect to ice (RHice) have been observed in subvisible cirrus clouds located near the cold point tropopause at extremely low temperatures around 180 K. Although further observational evidence is needed to confirm the credibility of such high values of RHice, the evolution of TTL dehydration is evident from the data in isentropic scatter plots between the sonde-observed mixing ratio (OMR) and the minimum saturation mixing ratio (SMRmin) along the back trajectories associated with the observed air mass. Supersaturation exceeding the critical value of homogeneous ice nucleation (OMR > 1.6 x SMRmin) is frequently observed on the 360 and 365K surfaces indicating that cold trap dehydration is in progress in the TTL. The near correspondence between the two (OMR similar to SMRmin) at 380K on the other hand implies that this surface is not sufficiently cold for the advected air parcels to be dehydrated. Above 380 K, cold trap dehydration would scarcely function while some moistening occurs before the air parcels reach the lowermost stratosphere at around 400K where OMR is generally smaller than SMRmin.
  • G. A. Morris, G. Labow, H. Akimoto, M. Takigawa, M. Fujiwara, F. Hasebe, J. Hirokawa, T. Koide
    ATMOSPHERIC CHEMISTRY AND PHYSICS 13 3 1243 - 1260 2013年 [査読有り][通常論文]
     
    In submitting data to the World Meteorological Organization (WMO) World Ozone and Ultraviolet Data Center (WOUDC), numerous ozonesonde stations include a correction factor (CF) that multiplies ozone concentration profile data so that the columns computed agree with column measurements from co-located ground-based and/or overpassing satellite instruments. We evaluate this practice through an examination of data from four Japanese ozonesonde stations: Kagoshima, Naha, Sapporo, and Tsukuba. While agreement between the sonde columns and Total Ozone Mapping Spectrometer (TOMS) or Ozone Mapping Instrument (OMI) is improved by use of the CF, agreement between the sonde ozone concentrations reported near the surface and data from surface monitors near the launch sites is negatively impacted. In addition, we find the agreement between the mean sonde columns without the CF and the ground-based Dobson instrument columns is improved by similar to 1.5% by using the McPeters et al. (1997) balloon burst climatology rather than the constant mixing ratio assumption (that has been used for the data in the WOUDC archive) for the above burst height column estimate. Limited comparisons of coincident ozonesonde profiles from Hokkaido University with those in the WOUDC database suggest that while the application of the CFs in the stratosphere improves agreement, it negatively impacts the agreement in the troposphere. Finally and importantly, unexplained trends and changing trends in the CFs appear over the last 20 years. The overall trend in the reported CFs for the four Japanese ozonesonde stations from 1990-2010 is (-0.264+/-0.036) x 10(-2) yr(-1); but from 1993-1999 the trend is (-2.18+/-0.14) x 10(-2) yr(-1) and from 1999-2009 is (1.089+/-0.075) x 10(-2) yr(-1), resulting in a statistically significant difference in CF trends between these two periods of (3.26+/-0.16) x 10(-2) yr(-1). Repeating the analysis using CFs derived from columns computed using the balloon-burst climatology, the trends are somewhat reduced, but remain statistically significant. Given our analysis, we recommend the following: (1) use of the balloon burst climatology is preferred to a constant mixing ratio assumption for determining total column ozone with sonde data; (2) if CFs are applied, their application should probably be restricted to altitudes above the tropopause; (3) only sondes that reach at least 32 km (10.5 hPa) before bursting should be used in data validation and/or ozone trend studies if the constant mixing ratio assumption is used to calculate the above burst column (as is the case for much of the data in the WOUDC archive). Using the balloon burst climatology, sondes that burst above 29 km (similar to 16 hPa), and perhaps lower, can be used; and (4) all ozone trend studies employing Japanese sonde data should be revisited after a careful examination of the impact of the CF on the calculated ozone trends.
  • Y. Inai, F. Hasebe, M. Fujiwara, M. Shiotani, N. Nishi, S. Y. Ogino, H. Vömel, S. Iwasaki, T. Shibata
    Atmospheric Chemistry and Physics 13 17 8623 - 8642 2013年 [査読有り][通常論文]
     
    We apply the match technique, whereby the same air mass is observed more than once and such cases are termed a "match", to study the dehydration process associated with horizontal advection in the tropical tropopause layer (TTL) over the western Pacific. The matches are obtained from profile data taken by the Soundings of Ozone and Water in the Equatorial Region (SOWER) campaign network observations using isentropic trajectories calculated from European Centre for Medium-Range Weather Forecasts (ECMWF) operational analyses. For the matches identified, extensive screening procedures are performed to verify the representativeness of the air parcel and the validity of the isentropic treatment, and to check for possible water injection by deep convection, consistency between the sonde data and analysis field referring to the ozone conservation. Among the matches that passed the screening tests, we identified some cases corresponding to the first quantitative value of dehydration associated with horizontal advection in the TTL. The statistical features of dehydration for the air parcels advected in the lower TTL are derived from the matches. The threshold of nucleation is estimated to be 146 ± 1% (1σ) in relative humidity with respect to ice (RHice), while dehydration seems to continue until RHice reaches about 75 ± 23% (1σ) in the altitude region from 350 to 360 K. The efficiency of dehydration expressed by the relaxation time required for the supersaturated air parcel to approach saturation is empirically determined from the matches. A relaxation time of approximately one hour reproduces the second water vapor observation reasonably well, given the first observed water vapor amount and the history of the saturation mixing ratio during advection in the lower TTL. © 2013 Author(s).
  • Anne M. Thompson, Sonya K. Miller, Simone Tilmes, Debra W. Kollonige, Jacquelyn C. Witte, Samuel J. Oltmans, Bryan J. Johnson, Masatomo Fujiwara, F. J. Schmidlin, G. J. R. Coetzee, Ninong Komala, Matakite Maata, Maznorizan Bt Mohamad, J. Nguyo, C. Mutai, S-Y. Ogino, F. Raimundo Da Silva, N. M. Paes Leme, Francoise Posny, Rinus Scheele, Henry B. Selkirk, Masato Shiotani, Rene Stuebi, Gilbert Levrat, Bertrand Calpini, Valerie Thouret, Haruo Tsuruta, Jessica Valverde Canossa, Holger Voemel, S. Yonemura, Jorge Andres Diaz, Nguyen T. Tan Thanh, Hoang T. Thuy Ha
    JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 117 2012年12月 [査読有り][通常論文]
     
    We present a regional and seasonal climatology of SHADOZ ozone profiles in the troposphere and tropical tropopause layer (TTL) based on measurements taken during the first five years of Aura, 2005-2009, when new stations joined the network at Hanoi, Vietnam; Hilo, Hawaii; Alajuela/Heredia, Costa Rica; Cotonou, Benin. In all, 15 stations operated during that period. A west-to-east progression of decreasing convective influence and increasing pollution leads to distinct tropospheric ozone profiles in three regions: (1) western Pacific/eastern Indian Ocean; (2) equatorial Americas (San Cristobal, Alajuela, Paramaribo); (3) Atlantic and Africa. Comparisons in total ozone column from soundings, the Ozone Monitoring Instrument (OMI, on Aura, 2004-) satellite and ground-based instrumentation are presented. Most stations show better agreement with OMI than they did for EP/TOMS comparisons (1998-2004; Earth-Probe/Total Ozone Mapping Spectrometer), partly due to a revised above-burst ozone climatology. Possible station biases in the stratospheric segment of the ozone measurement noted in the first 7 years of SHADOZ ozone profiles are re-examined. High stratospheric bias observed during the TOMS period appears to persist at one station. Comparisons of SHADOZ tropospheric ozone and the daily Trajectory-enhanced Tropospheric Ozone Residual (TTOR) product (based on OMI/MLS) show that the satellite-derived column amount averages 25% low. Correlations between TTOR and the SHADOZ sondes are quite good (typical r(2) = 0.5-0.8), however, which may account for why some published residual-based OMI products capture tropospheric interannual variability fairly realistically. On the other hand, no clear explanations emerge for why TTOR-sonde discrepancies vary over a wide range at most SHADOZ sites.
  • Y. Inai, T. Shibata, M. Fujiwara, F. Hasebe, H. Voemel
    GEOPHYSICAL RESEARCH LETTERS 39 2012年10月 [査読有り][通常論文]
     
    The relationship between relative humidity and cirrus clouds in the tropical tropopause layer (TTL) is investigated using balloon-borne cryogenic frostpoint hygrometers (CFH) and quasi-collocated measurements of space-borne Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) over Biak (1.17 degrees S, 136.06 degrees E) and Kototabang (0.20 degrees S, 100.32 degrees E) both in Indonesia in Januaries 2007 and 2008. At Kototabang, thin layers of high supersaturation, up to similar to 160% in relative humidity with respect to ice (RHi), are often observed co-existing with cirrus clouds at altitudes of similar to 15-18 km. At Biak, RHi inside cirrus is around 100% or less without large supersaturation layers, and most clouds are limited to altitudes below 16 km. We found that the presence and the degree of supersaturation may strongly depend on the phases of large-scale disturbances such as the MJO rather than geographical difference. Citation: Inai, Y., T. Shibata, M. Fujiwara, F. Hasebe, and H. Vmel (2012), High supersaturation inside cirrus in well-developed tropical tropopause layer over Indonesia, Geophys. Res. Lett., 39, L20811, doi:10.1029/2012GL053638.
  • H. Kubokawa, M. Fujiwara, T. Nasuno, M. Miura, M. K. Yamamoto, M. Satoh
    JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 117 2012年09月 [査読有り][通常論文]
     
    The roles of deep convection and generated waves in the Tropical Tropopause Layer (TTL) are investigated using a global nonhydrostatic model, the Nonhydrostatic Icosahedral Atmospheric Model (NICAM), which runs on the Earth Simulator with a horizontal spacing of 7 km. The model data, which successfully simulated a Madden-Julian Oscillation (MJO) event for the period between 15 December 2006 and 15 January 2007, are analyzed. The frequency of deep convective clouds that reach the TTL is one of the key diagnostics for dehydration and transport. The present results revealed that the proportion of cumulus clouds that penetrate the lapse-rate tropopause and the bottom boundary of the TTL (defined as the lapse rate minimum) is similar to 0.5% and similar to 20%, respectively, in the region between 5 degrees S and 5 degrees N. This result is reasonably consistent with atmospheric observations. Deep convective activity that reaches the TTL was observed over southern Africa, the Indian Ocean, the Indonesian maritime continent, the western Pacific, and southern America. Deep convection over the continents was most active during the local evening period. Over the oceans, high clouds reaching the tropopause were seen over the Indian Ocean and the seas around Java, where two tropical cyclones were generated. Prominent diurnal variations in tropopause temperature associated with deep convection occurred over the Indonesian maritime continent. These diurnal variations were superimposed on large, low-frequency temperature variations associated with equatorial Kelvin waves generated by the MJO convection. Probably because of coarse vertical resolution, temperature variations simulated by the NICAM are larger than those in the real atmosphere. The two tropical cyclones caused relatively large tropopause temperature variations with a cyclone scale (similar to 500 km horizontally). The gravity waves generated by tropical cyclones cause small tropopause temperature variations that extend for 1000 km from the cyclone. We conclude that the Kelvin waves associated with the MJO convection cause the largest amplitude of temperature variations in the TTL and that tropical cyclones and diurnal variations of convective activity have large local impacts on temperature variations in the TTL.
  • T. Sakazaki, M. Fujiwara, X. Zhang, M. E. Hagan, J. M. Forbes
    JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 117 2012年07月 [査読有り][通常論文]
     
    We compare and examine diurnal temperature tides including their migrating component (DW1) from the troposphere to the lower mesosphere, using data from Thermosphere-Ionosphere-Mesosphere-Energetics and Dynamics/Sounding of the Atmosphere using Broadband Emission Radiometry (TIMED/SABER) and from six different reanalysis data sets: (1) the Modern Era Retrospective analysis for Research and Applications (MERRA), (2) the European Centre for Medium-range Weather Forecasts (ECMWF) reanalysis (ERA-Interim) (3) the National Centers for Environmental Prediction (NCEP) Climate Forecast System Reanalysis (CFSR), (4) the Japanese 25-year reanalysis by Japanese Meteorological Agency (JMA) and the Central Research Institute of Electric Power Industry (CRIEPI) (JRA25), (5) the NCEP/National Center for Atmospheric Research reanalysis (NCEP1), and (6) the NCEP and Department of Energy (DOE) Atmospheric Model Intercomparison Project (AMIP-II) reanalysis data (NCEP2). The horizontal and vertical structures of the diurnal tides in SABER and reanalyses reasonably agree, although the amplitudes are up to 30-50% smaller in the reanalyses than in the SABER in the upper stratosphere to lower mesosphere. Of all tidal components, the DW1 is dominant while a clear eastward propagating zonal wave number 3 component (DE3) is observed at midlatitudes of the Southern Hemisphere in winter. Among the six reanalyses, MERRA, ERA-Interim and CFSR are better at reproducing realistic diurnal tides. It is found that the diurnal tides extracted from SABER data in the winter-hemisphere stratosphere suffer from sampling issues that are caused by short-term variations of the background temperature. In addition, the GSWM underestimates the amplitude in the midlatitude upper stratosphere by about 50%.
  • M. Fujiwara, J. Suzuki, A. Gettelman, M. I. Hegglin, H. Akiyoshi, K. Shibata
    JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 117 2012年06月 [査読有り][通常論文]
     
    Sub-seasonal variability including equatorial waves significantly influence the dehydration and transport processes in the tropical tropopause layer (TTL). This study investigates the wave activity in the TTL in 7 reanalysis data sets (RAs; NCEP1, NCEP2, ERA40, ERA-Interim, JRA25, MERRA, and CFSR) and 4 chemistry climate models (CCMs; CCSRNIES, CMAM, MRI, and WACCM) using the zonal wave number-frequency spectral analysis method with equatorially symmetric-antisymmetric decomposition. Analyses are made for temperature and horizontal winds at 100 hPa in the RAs and CCMs and for outgoing longwave radiation (OLR), which is a proxy for convective activity that generates tropopause-level disturbances, in satellite data and the CCMs. Particular focus is placed on equatorial Kelvin waves, mixed Rossby-gravity (MRG) waves, and the Madden-Julian Oscillation (MJO). The wave activity is defined as the variance, i.e., the power spectral density integrated in a particular zonal wave number-frequency region. It is found that the TTL wave activities show significant difference among the RAs, ranging from similar to 0.7 (for NCEP1 and NCEP2) to similar to 1.4 (for ERA-Interim, MERRA, and CFSR) with respect to the averages from the RAs. The TTL activities in the CCMs lie generally within the range of those in the RAs, with a few exceptions. However, the spectral features in OLR for all the CCMs are very different from those in the observations, and the OLR wave activities are too low for CCSRNIES, CMAM, and MRI. It is concluded that the broad range of wave activity found in the different RAs decreases our confidence in their validity and in particular their value for validation of CCM performance in the TTL, thereby limiting our quantitative understanding of the dehydration and transport processes in the TTL.
  • T. Shibata, M. Hayashi, A. Naganuma, N. Hara, K. Hara, F. Hasebe, K. Shimizu, N. Komala, Y. Inai, H. Voemel, S. Hamdi, S. Iwasaki, M. Fujiwara, M. Shiotani, S-Y. Ogino, N. Nishi
    JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 117 2012年06月 [査読有り][通常論文]
     
    An aerosol layer was found 1-2 km around the tropical cold point tropopause by observations using ground-based lidar and balloon-borne optical particle counters (OPC) over Biak, Indonesia, in January 2011. The layer was observed throughout the survey period from 6 to 13 January. The backscattering coefficient of the layer was about 5 times larger than that of the background aerosols. The lidar-observed depolarization ratio of the layer was very low, and the wavelength dependence of the backscattering coefficients of the layer was similar to that of stratospheric aerosols. A layer of the particles at the size of the accumulation mode was also observed by an OPC at ambient temperature, but the particles were volatile at 200 degrees C. These properties indicate that the aerosol layer was composed of liquid phase aqueous sulfuric acid solution particles and probably originated from a volcanic eruption. It was observed by lidar that a thin cirrus cloud layer appeared within this aerosol layer. Backward trajectory analysis and satellite-observed equivalent blackbody temperature indicate that the cirrus cloud layer probably formed in situ. The estimated upper limit of the number concentration of cloud particles was 10(5) m(-3). The number concentration of the volatile aerosol particles (similar to 3 x 10(6) m(-3)) was 30 times larger than this upper limit. This upper limit, however, is comparable to the aerosol particle concentration observed by the OPC at 200 degrees C. These results are consistent with the cirrus cloud formation with solid sulfate particles in tropical upper troposphere suggested by previous studies.
  • Anne M. Thompson, Sonya K. Miller, Simone Tilmes, Debra W. Kollonige, Jacquelyn C. Witte, Samuel J. Oltmans, Bryan J. Johnson, Masatomo Fujiwara, F. J. Schmidlin, G. J.R. Coetzee, Ninong Komala, Matakite Maata, Maznorizan Bt Mohamad, J. Nguyo, C. Mutai, S. Y. Ogino, F. Raimundo Da Silva, N. M. Paes Leme, Francoise Posny, Rinus Scheele, Henry B. Selkirk, Masato Shiotani, René Stbi, Gilbert Levrat, Bertrand Calpini, Valérie Thouret, Haruo Tsuruta, Jessica Valverde Canossa, Holger Vmel, S. Yonemura, Jorge Andrés Diaz, Nguyen T. Tan Thanh, Hoang T. Thuy Ha
    Journal of Geophysical Research Atmospheres 117 23 2012年 [査読有り][通常論文]
     
    We present a regional and seasonal climatology of SHADOZ ozone profiles in the troposphere and tropical tropopause layer (TTL) based on measurements taken during the first five years of Aura, 2005-2009, when new stations joined the network at Hanoi, Vietnam Hilo, Hawaii Alajuela/Heredia, Costa Rica Cotonou, Benin. In all, 15 stations operated during that period. A west-to-east progression of decreasing convective influence and increasing pollution leads to distinct tropospheric ozone profiles in three regions: (1) western Pacific/eastern Indian Ocean (2) equatorial Americas (San Cristóbal, Alajuela, Paramaribo) (3) Atlantic and Africa. Comparisons in total ozone column from soundings, the Ozone Monitoring Instrument (OMI, on Aura, 2004-) satellite and ground-based instrumentation are presented. Most stations show better agreement with OMI than they did for EP/TOMS comparisons (1998-2004 Earth-Probe/Total Ozone Mapping Spectrometer), partly due to a revised above-burst ozone climatology. Possible station biases in the stratospheric segment of the ozone measurement noted in the first 7 years of SHADOZ ozone profiles are re-examined. High stratospheric bias observed during the TOMS period appears to persist at one station. Comparisons of SHADOZ tropospheric ozone and the daily Trajectory-enhanced Tropospheric Ozone Residual (TTOR) product (based on OMI/MLS) show that the satellite-derived column amount averages 25% low. Correlations between TTOR and the SHADOZ sondes are quite good (typical r< sup> 2< /sup> = 0.5-0.8), however, which may account for why some published residual-based OMI products capture tropospheric interannual variability fairly realistically. On the other hand, no clear explanations emerge for why TTOR-sonde discrepancies vary over a wide range at most SHADOZ sites. © 2012. American Geophysical Union. All Rights Reserved.
  • T. Sakazaki, M. Fujiwara, H. Hashiguchi
    JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 115 2010年12月 [査読有り][通常論文]
     
    Diurnal variations in the troposphere are a source of the diurnal tides which are the prevalent dynamical phenomenon in the mesosphere and lower thermosphere. They are also discussed as contributing to the excitation of Rossby waves. Here we study diurnal variations of upper tropospheric and lower stratospheric winds (up to 22 km) over Japan from 1986 to 2008 mainly using data from the middle and upper atmosphere (MU) radar (34.85 degrees N, 136.10 degrees E) and JRA25/JCDAS data, as well as other four global reanalysis data sets (ERA40, ERA-Interim, NCEP1, and NCEP2) and output data from Global Scale Wave Model (GSWM). The diurnal and semidiurnal components are extracted and analyzed. For the diurnal wind component, the MU radar data are used to validate the reanalysis data, and the reanalysis data are chosen for the analysis. The diurnal amplitude monotonically increases with height above 15-20 km. The diurnal phase shows an upward progression up to 15 to 20 km, while above 15 to 20 km, it shows a downward progression in most months. It is found that the diurnal tide, defined as the diurnal component with absolute zonal wave numbers of <= 6, is dominant in the upper troposphere (explaining 60 to 80% of the variance) and in the stratosphere (explaining 80 to 90% of the variance). It is also observed that medium-scale waves contributed to the diurnal wind component in the upper troposphere from winter to spring (similar to 20% of the variance). For the semidiurnal wind component, only MU radar data are used for the analysis, which confirmed that the semidiurnal migrating tide is dominant through the troposphere and the lower stratosphere. The semidiurnal tidal amplitude shows a marked seasonal variation in the troposphere; the amplitude is largest in winter (similar to 0.4 m s(-1)) and smallest in summer (similar to 0.2 m s(-1)).
  • A. Gettelman, M. I. Hegglin, S. -W. Son, J. Kim, M. Fujiwara, T. Birner, S. Kremser, M. Rex, J. A. Anel, H. Akiyoshi, J. Austin, S. Bekki, P. Braesike, C. Bruehl, N. Butchart, M. Chipperfield, M. Dameris, S. Dhomse, H. Garny, S. C. Hardiman, P. Joeckel, D. E. Kinnison, J. F. Lamarque, E. Mancini, M. Marchand, M. Michou, O. Morgenstern, S. Pawson, G. Pitari, D. Plummer, J. A. Pyle, E. Rozanov, J. Scinocca, T. G. Shepherd, K. Shibata, D. Smale, H. Teyssedre, W. Tian
    JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 115 2010年10月 [査読有り][通常論文]
     
    The performance of 18 coupled Chemistry Climate Models (CCMs) in the Tropical Tropopause Layer (TTL) is evaluated using qualitative and quantitative diagnostics. Trends in tropopause quantities in the tropics and the extratropical Upper Troposphere and Lower Stratosphere (UTLS) are analyzed. A quantitative grading methodology for evaluating CCMs is extended to include variability and used to develop four different grades for tropical tropopause temperature and pressure, water vapor and ozone. Four of the 18 models and the multi-model mean meet quantitative and qualitative standards for reproducing key processes in the TTL. Several diagnostics are performed on a subset of the models analyzing the Tropopause Inversion Layer (TIL), Lagrangian cold point and TTL transit time. Historical decreases in tropical tropopause pressure and decreases in water vapor are simulated, lending confidence to future projections. The models simulate continued decreases in tropopause pressure in the 21st century, along with similar to 1K increases per century in cold point tropopause temperature and 0.5-1 ppmv per century increases in water vapor above the tropical tropopause. TTL water vapor increases below the cold point. In two models, these trends are associated with 35% increases in TTL cloud fraction. These changes indicate significant perturbations to TTL processes, specifically to deep convective heating and humidity transport. Ozone in the extratropical lowermost stratosphere has significant and hemispheric asymmetric trends. O-3 is projected to increase by nearly 30% due to ozone recovery in the Southern Hemisphere (SH) and due to enhancements in the stratospheric circulation. These UTLS ozone trends may have significant effects in the TTL and the troposphere.
  • M. Fujiwara, H. Voemel, F. Hasebe, M. Shiotani, S-Y. Ogino, S. Iwasaki, N. Nishi, T. Shibata, K. Shimizu, E. Nishimoto, J. M. Valverde Canossa, H. B. Selkirk, S. J. Oltmans
    JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 115 2010年09月 [査読有り][通常論文]
     
    We investigated water vapor variations in the tropical lower stratosphere on seasonal, quasi-biennial oscillation (QBO), and decadal time scales using balloon-borne cryogenic frost point hygrometer data taken between 1993 and 2009 during various campaigns including the Central Equatorial Pacific Experiment (March 1993), campaigns once or twice annually during the Soundings of Ozone and Water in the Equatorial Region (SOWER) project in the eastern Pacific (1998-2003) and in the western Pacific and Southeast Asia (2001-2009), and the Ticosonde campaigns and regular sounding at Costa Rica (2005-2009). Quasi-regular sounding data taken at Costa Rica clearly show the tape recorder signal. The observed ascent rates agree well with the ones from the Halogen Occultation Experiment (HALOE) satellite sensor. Average profiles from the recent five SOWER campaigns in the equatorial western Pacific in northern winter and from the three Ticosonde campaigns at Costa Rica (10 N) in northern summer clearly show two effects of the QBO. One is the vertical displacement of water vapor profiles associated with the QBO meridional circulation anomalies, and the other is the concentration variations associated with the QBO tropopause temperature variations. Time series of cryogenic frost point hygrometer data averaged in a lower stratospheric layer together with HALOE and Aura Microwave Limb Sounder data show the existence of decadal variations: The mixing ratios were higher and increasing in the 1990s, lower in the early 2000s, and probably slightly higher again or recovering after 2004. Thus linear trend analysis is not appropriate to investigate the behavior of the tropical lower stratospheric water vapor.
  • Takatoshi Sakazaki, Masatomo Fujiwara
    JOURNAL OF THE METEOROLOGICAL SOCIETY OF JAPAN 88 3 349 - 372 2010年06月 [査読有り][通常論文]
     
    Following on from the observation results obtained from Wind profiler Network and Data Acquisition System (WINDAS) data, as reported by Part I of this study, the dynamical processes responsible for the diurnal component in lower-tropospheric winds are examined using Japan Meteorological Agency (JMA) mesoscale analysis data (MANAL) and four global reanalysis data sets (JRA25/JCDAS, ERA-Interim, NCEP1, and NCEP2). Of these data sets, MANAL and JRA25 perform best in reproducing the WINDAS horizontal wind observations, including their diurnal and semidiurnal components. At 1-3 km height, Diurnal Eastward-moving Eddies (DEEs) with a phase speed of 10-15 m s(-1) and diameter of similar to 700 km move eastward over the Sea of Japan and over the Pacific throughout the year. The superposition of winds associated with DEEs over return currents controls the diurnal wind component over the main Japanese islands, generating diurnal amplitude maxima in spring and autumn at this height range. Analysis of global reanalysis data confirmed that the diurnal wind at 3-5 km in winter-spring is controlled mainly by medium-scale eastward-traveling waves with amplitude maxima around the tropopause. The diurnal wind at 3-5 km in summer-autumn is caused primarily by the diurnal tide with zonal wavenumbers of <= 10. For stations located on small islands south of the Japanese mainland, the diurnal wind is controlled mainly by the diurnal tide for the entire lower troposphere throughout the year.
  • Takatoshi Sakazaki, Masatomo Fujiwara
    JOURNAL OF THE METEOROLOGICAL SOCIETY OF JAPAN 88 3 325 - 347 2010年06月 [査読有り][通常論文]
     
    This study investigates diurnal variations in lower-tropospheric wind over Japan during 2002-2008 using data from 31 stations of the Wind profiler Network and Data Acquisition System (WINDAS) and the Automated Meteorological Data Acquisition System (AMeDAS). The diurnal and semidiurnal components are extracted and analyzed to identify the dominant processes for each height range and for each season. Near the surface, the diurnal component is controlled by local wind systems (e.g., land-sea breezes) throughout the year. At 1-3 km, the diurnal component is primarily controlled by the return currents of local wind systems, with additional influence by other disturbances: the superposition of these two wind systems generates amplitude maxima in spring (similar to 0.5 m s(-1)) and autumn (similar to 0.6 m s(-1)). At 3-5 km, the diurnal wind in DJF-MAM is controlled by medium-scale eastward traveling waves, which generate the amplitude maximum (similar to 0.8 m s(-1)) in winter-spring. In JJA-SON, the diurnal component is controlled by a large-scale wind system with an amplitude of similar to 0.3 m s(-1), probably related to the diurnal tide. At stations located on small islands located south of the Japanese mainland, the diurnal wind within the lower troposphere has different characteristics from those described above throughout the year. Throughout Japan, the semidiurnal wind component is controlled by the semidiurnal migrating tide above similar to 1 km, and is influenced by local wind systems below similar to 1 km. The amplitude of the semidiurnal tide below 5 km is largest in DJF (similar to 0.4 m s(-1)) and smallest in JJA (similar to 0.2 m s(-1)).
  • H. Kubokawa, M. Fujiwara, T. Nasuno, M. Satoh
    JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 115 2010年04月 [査読有り][通常論文]
     
    The dynamical characteristics of the tropical tropopause layer (TTL) are investigated using the Nonhydrostatic Icosahedral Atmospheric Model (NICAM) run on the Earth Simulator under an aqua planet condition. Two experiments are performed: one with a 3.5 km horizontal spacing and a three-dimensional snapshot output and another with a 7 km horizontal spacing and 3-hourly averages for 1 month. The number of vertical levels is 54 and the model top is at 40 km; the vertical spacing in and around the TTL is similar to 700 m. Large-scale organized convection associated with convectively coupled equatorial Kelvin waves prevails around the equator. The zonal mean vertical distribution of cloud top height near the equator shows a realistic trimodal structure. The simulation results reveal that cumulus clouds penetrate the lapse-rate tropopause and the bottom boundary of the TTL (defined as the lapse rate minimum) for similar to 0.1% and similar to 25%, respectively, in the equatorial area. The frequency distribution of vertical wind may provide a good indicator of the TTL bottom boundary. A significant reduction in the speed of strong vertical winds is observed at similar to 16 km. High variability in temperature and the water vapor mixing ratio observed around the tropopause is mainly caused by equatorial Kelvin waves generated by the organized convection in these experiments. Horizontal variability in tropopause height over a large-scale convective system is much smaller than that in the area of Kelvin waves. The gravity waves generated by this large-scale convective system locally control the temperature around the tropopause. In addition, large-amplitude gravity waves with a scale of 600 km are superimposed on the cold phase of Kelvin waves, producing one of the coldest regions around the tropopause. It is suggested that the combination of Kelvin waves and gravity waves may be one of the most effective dehydration processes in the TTL.
  • H. Kubokawa, M. Fujiwara, T. Nasuno, M. Satoh
    Journal of Geophysical Research Atmospheres 115 8 2010年 [査読有り][通常論文]
     
    The dynamical characteristics of the tropical tropopause layer (TTL) are investigated using the Nonhydrostatic Icosahedral Atmospheric Model (NICAM) run on the Earth Simulator under an aqua planet condition. Two experiments are performed: one with a 3.5 km horizontal spacing and a three-dimensional snapshot output and another with a 7 km horizontal spacing and 3-hourly averages for 1 month. The number of vertical levels is 54 and the model top is at 40 km the vertical spacing in and around the TTL is ̃700 m. Large-scale organized convection associated with convectively coupled equatorial Kelvin waves prevails around the equator. The zonal mean vertical distribution of cloud top height near the equator shows a realistic trimodal structure. The simulation results reveal that cumulus clouds penetrate the lapse-rate tropopause and the bottom boundary of the TTL (defined as the lapse rate minimum) for ̃0.1% and ̃25%, respectively, in the equatorial area. The frequency distribution of vertical wind may provide a good indicator of the TTL bottom boundary. A significant reduction in the speed of strong vertical winds is observed at ̃16 km. High variability in temperature and the water vapor mixing ratio observed around the tropopause is mainly caused by equatorial Kelvin waves generated by the organized convection in these experiments. Horizontal variability in tropopause height over a large-scale convective system is much smaller than that in the area of Kelvin waves. The gravity waves generated by this large-scale convective system locally control the temperature around the tropopause. In addition, large-amplitude gravity waves with a scale of 600 km are superimposed on the cold phase of Kelvin waves, producing one of the coldest regions around the tropopause. It is suggested that the combination of Kelvin waves and gravity waves may be one of the most effective dehydration processes in the TTL. Copyright 2010 by the American Geophysical Union.
  • Junko Suzuki, Masatomo Fujiwara, Atsushi Hamada, Yoichi Inai, Jun Yamaguchi, Ryuichi Shirooka, Fumio Hasebe, Toshiaki Takano
    SOLA 6 97 - 100 2010年 [査読有り][通常論文]
     
    Cloud-top height (CTH) variability in the tropical tropopause layer (TTL) in association with equatorial Kelvin waves is investigated using a new CTH dataset based on MTSAT-1R geostationary satellite measurements with a statistical look-up table constructed based on CloudSat measurements. We focus on a case in the tropical Indian Ocean during October-December 2006, when shipboard radiosonde, TTL water vapor, and 95-GHz cloud radar measurements were taken during the Mirai Indian Ocean cruise for the Study of the MJO-convection Onset (MISMO) field campaign. At 10-15 km, the satellite-based CTH data agree well with the radar echo top heights from shipboard radar reflectivity data. During the MISMO campaign, cloud frequency was suppressed in the warm phase of equatorial Kelvin waves propagating in the TTL. The suppressed-cloud region moves eastward to the western Pacific together with Kelvin waves. We found that changes in CTH occurrence frequency over the vessel in association with Kelvin waves are much greater than those associated with the diurnal cycle. It is expected that the phase of equatorial Kelvin waves is important for the intraseasonal variabilities of both the radiative budget of the tropical atmosphere and water vapor transport in the TTL.
  • M. Fujiwara, S. Iwasaki, A. Shimizu, Y. Inai, M. Shiotani, F. Hasebe, I. Matsui, N. Sugimoto, H. Okamoto, N. Nishi, A. Hamada, T. Sakazaki, K. Yoneyama
    Journal of Geophysical Research Atmospheres 114 9 D09304  2009年05月16日 [査読有り][通常論文]
     
    [1] A polarization lidar was continuously operated aboard the research vessel Mirai in the tropical western Pacific over three northern winters: at 2.0°N, 138.0°E during November and December 2001 at 2.0°N, 138.5°E during November and December 2002 and at 7.5°N, 134.0°E during December 2004 and January 2005. Intensive radiosonde soundings were made from the vessel at 3-h intervals during all three campaigns. The mechanisms that underlie the observed variations in cirrus in the tropical tropopause layer (TTL) are discussed from the viewpoint of large-scale dynamics and transport. During the 2001 campaign, the tropopause region was cold, but the TTL was often clear, with only some subvisual cirrus. Potential vorticity data and trajectories show that the TTL during this period was strongly affected by dry air transport from the northern midlatitude lower stratosphere. During the 2002 campaign, a packet of large-amplitude equatorial Kelvin waves was the primary control on the generation and disappearance of cirrus in the TTL. During the 2004-2005 campaign, a cold phase of large-scale waves resulted in cirrus generation in the TTL in late December of 2004, similar to that observed during the 2002 campaign. Outflow from the South Pacific Convergence Zone (SPCZ) caused optically thick cirrus in the TTL, particularly during early January 2005, when we also observed regular diurnal variations in cirrus development within the TTL, that is, apparent sedimentation during the nighttime. We investigated two possible controlling processes, namely, horizontal advection together with diurnal variations in convective activity within the SPCZ and diurnal variations in local temperature due to tides and gravity waves. In the equatorial western Pacific, equatorial Kelvin waves are the important dynamical process that controls cirrus variations in the TTL. Dry-air horizontal transport. from the midlatitude lower stratosphere and wet-air vertical transport near the tropical convergence regions should also be considered in fully explaining the cirrus observations in the TTL. Copyright 2009 by the American Geophysical Union.
  • M. Fujiwara, S. Iwasaki, A. Shimizu, Y. Inai, M. Shiotani, F. Hasebe, I. Matsui, N. Sugimoto, H. Okamoto, N. Nishi, A. Hamada, T. Sakazaki, K. Yoneyama
    JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 114 2009年05月 [査読有り][通常論文]
     
    A polarization lidar was continuously operated aboard the research vessel Mirai in the tropical western Pacific over three northern winters: at 2.0 degrees N, 138.0 degrees E during November and December 2001; at 2.0 degrees N, 138.5 degrees E during November and December 2002; and at 7.5 degrees N, 134.0 degrees E during December 2004 and January 2005. Intensive radiosonde soundings were made from the vessel at 3-h intervals during all three campaigns. The mechanisms that underlie the observed variations in cirrus in the tropical tropopause layer (TTL) are discussed from the viewpoint of large-scale dynamics and transport. During the 2001 campaign, the tropopause region was cold, but the TTL was often clear, with only some subvisual cirrus. Potential vorticity data and trajectories show that the TTL during this period was strongly affected by dry air transport from the northern midlatitude lower stratosphere. During the 2002 campaign, a packet of large-amplitude equatorial Kelvin waves was the primary control on the generation and disappearance of cirrus in the TTL. During the 2004-2005 campaign, a cold phase of large-scale waves resulted in cirrus generation in the TTL in late December of 2004, similar to that observed during the 2002 campaign. Outflow from the South Pacific Convergence Zone (SPCZ) caused optically thick cirrus in the TTL, particularly during early January 2005, when we also observed regular diurnal variations in cirrus development within the TTL, that is, apparent sedimentation during the nighttime. We investigated two possible controlling processes, namely, horizontal advection together with diurnal variations in convective activity within the SPCZ and diurnal variations in local temperature due to tides and gravity waves. In the equatorial western Pacific, equatorial Kelvin waves are the important dynamical process that controls cirrus variations in the TTL. Dry-air horizontal transport from the midlatitude lower stratosphere and wet-air vertical transport near the tropical convergence regions should also be considered in fully explaining the cirrus observations in the TTL.
  • Yoichi Inai, Fumio Hasebe, Kensaku Shimizu, Masatomo Fujiwara
    SOLA 5 109 - 112 2009年 [査読有り][通常論文]
     
    A method of correction for radiosonde pressure and temperature data by using simultaneous global positioning system (GPS) ellipsoidal height (z(GPS)) is proposed. The correction is made by adjusting the observed pressure and temperature so that the ellipsoidal height (z(PTU)) calculated from integrating the hypsometric equation by using the latitude- and altitude-dependent gravity together with the observed pressure, temperature and humidity (PTU) agrees with z(GPS). The temperature bias is assumed to arise only from inaccurate radiation correction so that there is no temperature bias in the nighttime data. Under this assumption, the deviations of z(PTU) from z(GPS) in the nighttime data result only from observational errors in pressure. The pressure adjustment required to remove these deviations is applied also to the daytime data. The daytime temperature bias can then be estimated from the difference between z(PTU) and z(GPS) during the day. The biases in Vaisala RS80 pressure and temperature measurements are estimated using the Soundings of Ozone and Water in the Equatorial Region campaign data. The estimated pressure bias is positive below similar to 7 km and negative above it. The bias above 15 km is statistically significant. The daytime temperature bias lacks statistical significance due to fluctuations in the results.
  • Takatoshi Sakazaki, Masatomo Fujiwara
    JOURNAL OF THE METEOROLOGICAL SOCIETY OF JAPAN 86 5 787 - 803 2008年10月 [査読有り][通常論文]
     
    This study investigates diurnal variations in surface wind in Japan during June-August of 1992-2006 using data from the Automated Meteorological Data Acquisition System (AMeDAS) and the Sapporo City Multisensor (MULTI). Harmonic analysis and hodograph analysis are employed to investigate the rotation direction and rotation rate of the wind vector at about 1000 stations. An analysis of six major plains in Japan reveals distinct clockwise and anticlockwise hodograph regions within each plain. The rotation direction is attributed to two lagged pressure-gradient forces of contrasting orientations: one between the land and sea, and another between the plain and adjacent mountains. An analysis of the linearized equations of motion reveals that rotation of the wind vector is mainly controlled by the balance between the pressure gradient force and the frictional force, with a small but non-negligible contribution by the Coriolis force, particularly near the coast. The observed rotation rates of the hodographs show a brief stagnation during the mid-afternoon and a longer stagnation during the nighttime. This irregular rotation rate is well explained by taking into account the semidiurnal component of the wind. The linearized equations of motion indicate that this semidiurnal component results from the semidiurnal component of the pressure gradient force, which is generated by non-sinusoidal solar heating over the course of a day.
  • Hisahiro Takashima, M. Shiotani, M. Fujiwara, N. Nishi, F. Hasebe
    Journal of Geophysical Research Atmospheres 113 10 2008年05月27日 [査読有り][通常論文]
     
    Ozone and water vapor observations have been conducted at Christmas/ Kiritimati Island (2°N, 157°W) in the equatorial central Pacific as a part of the Soundings of Ozone and Water in the Equatorial Region (SOWER)/Pacific mission. We launched 33 ozonesondes and 33 chilled-mirror hygrometers in nine observation campaigns from 1999 to 2003 for various seasons. We found that ozone concentrations at Christmas Island are low in the whole troposphere (∼10-35 ppbv), particularly in the marine boundary layer (MBL). Ozone variation is small throughout the year compared with other tropical stations, though annual and interannual variations of meteorological fields are large over the equatorial central Pacific. Just below the tropopause, during the August 2002 campaign, we observed substantially reduced ozone concentrations (< 10 ppbv) similar to those found in the MBL, which are maintained at least for the observation period. From meteorological conditions, we found that air mass was advected from the Inter-Tropical Convergence Zone (ITCZ), located to the north of Christmas Island, in accordance with the northeasterly wind that is only observed during northern summer in the upper troposphere. The origin of air mass is supposed to be from the MBL in the ITCZ. Copyright 2008 by the American Geophysical Union.
  • F. Immler, K. Krueger, M. Fujiwara, G. Verver, M. Rex, O. Schrems
    ATMOSPHERIC CHEMISTRY AND PHYSICS 8 14 4019 - 4026 2008年 [査読有り][通常論文]
     
    A number of field-campaigns in the tropics have been conducted in recent years with two different LIDAR systems at Paramaribo (5.8 degrees N, 55.2 degrees W), Suriname. The lidars detect particles in the atmosphere with high vertical and temporal resolution and are capable of detecting extremely thin cloud layers which frequently occur in the tropical tropopause layer (TTL). Radiosonde as well as operational ECMWF analysis showed that equatorial Kelvin waves propagated in the TTL and greatly modulated its temperature structure. We found a clear correlation between the temperature anomalies introduced by these waves and the occurrence of thin cirrus in the TTL. In particular we found that extremely thin ice clouds form regularly where cold anomalies shift the tropopause to high altitudes. These findings suggest an influence of Kelvin wave activity on the dehydration in the TTL and thus on the global stratospheric water vapour concentration.
  • Kunio Yoneyama, Mikiko Fujita, Naoki Sato, Masatomo Fujiwara, Yoichi Inai, Fumio Hasebe
    SOLA 4 13 - 16 2008年 [査読有り][通常論文]
     
    Atmospheric soundings using the Vaisala RS92 radiosonde were intensively conducted during the field experiment MISMO (Mirai Indian Ocean cruise for the Study of the MJO-convection Onset) in the central and eastern equatorial Indian Ocean from October to December 2006. By comparing the RS92 relative humidity data with that from the Meteolabor Snow White (SW) chilled-mirror dew/frost-point hygrometers launched on the same ship around the local noon time, the dry bias was found to increase significantly with height. In addition, it was also revealed that the dry bias had a clear diurnal variation with its maximum at local noon and near-zero at night from the comparison of precipitable water vapor (PWV) with that derived from the shipboard Global Positioning System (GPS) data. Therefore, the dry bias of the RS92 data could be attributed to a solar radiation-induced error that was recently discussed by Vomel et al. (2007). In this study, we developed a correction scheme for the MISMO RS92 humidity data as a function of pressure and local time using SW data, and then confirmed its validity with GPS-derived PWV.
  • Holger Vömel, J. E. Barnes, R. N. Forno, M. Fujiwara, F. Hasebe, S. Iwasaki, R. Kivi, N. Komala, E. Kyrö, T. Leblanc, B. Morel, S. Y. Ogino, W. G. Read, S. C. Ryan, S. Saraspriya, H. Selkirk, M. Shiotani, J. Valverde Canossa, D. N. Whiteman
    Journal of Geophysical Research Atmospheres 112 24 2007年12月27日 [査読有り][通常論文]
     
    Here we present extensive observations of stratospheric and upper tropospheric water vapor using the balloon-borne Cryogenic Frost point Hygrometer (CFH) in support of the Aura Microwave Limb Sounder (MLS) satellite instrument. Coincident measurements were used for the validation of MLS version 1.5 and for a limited validation of MLS version 2.2 water vapor. The sensitivity of MLS is on average 30% lower than that of CFH, which is fully compensated by a constant offset at stratospheric levels but only partially compensated at tropospheric levels, leading to an upper tropospheric dry bias. The sensitivity of MLS observations may be adjusted using the correlation parameters provided here. For version 1.5 stratospheric observations at pressures of 68 hPa and smaller MLS retrievals and CFH in situ observations agree on average to within 2.3% ± 11.8%. At 100 hPa the agreement is to within 6.4% ± 22% and at upper tropospheric pressures to within 23% ± 37%. In the tropical stratosphere during the boreal winter the agreement is not as good. The "tape recorder" amplitude in MLS observations depends on the vertical profile of water vapor mixing ratio and shows a significant interannual variation. The agreement between stratospheric observations by MLS version 2.2 and CFH is comparable to the agreement using MLS version 1.5. The variability in the difference between observations by MLS version 2.2 and CFH at tropospheric levels is significantly reduced, but a tropospheric dry bias and a reduced sensitivity remain in this version. In the validation data set a dry bias at 177.8 hPa of -24.1% ± 16.0% is statistically significant. Copyright 2007 by the American Geophysical Union.
  • Y. B. Jiang, L. Froidevaux, A. Lambert, N. J. Livesey, W. G. Read, J. W. Waters, B. Bojkov, T. Leblanc, I. S. McDermid, S. Godin-Beekmann, M. J. Filipiak, R. S. Harwood, R. A. Fuller, W. H. Daffer, B. J. Drouin, R. E. Cofield, D. T. Cuddy, R. F. Jarnot, B. W. Knosp, V. S. Perun, M. J. Schwartz, W. V. Snyder, P. C. Stek, R. P. Thurstans, P. A. Wagner, M. Allaart, S. B. Andersen, G. Bodeker, B. Calpini, H. Claude, G. Coetzee, J. Davies, H. De Backer, H. Dier, M. Fujiwara, B. Johnson, H. Kelder, N. P. Leme, G. König-Langlo, E. Kyro, G. Laneve, L. S. Fook, J. Merrill, G. Morris, M. Newchurch, S. Oltmans, M. C. Parrondos, F. Posny, F. Schmidlin, P. Skrivankova, R. Stubi, D. Tarasick, A. Thompson, V. Thouret, P. Viatte, H. Vömel, P. von Der Gathen, M. Yela, G. Zablocki
    Journal of Geophysical Research Atmospheres 112 24 2007年12月27日 [査読有り][通常論文]
     
    We present validation studies of MLS version 2.2 upper tropospheric and stratospheric ozone profiles using ozonesonde and lidar data as well as climatological data. Ozone measurements from over 60 ozonesonde stations worldwide and three lidar stations are compared with coincident MLS data. The MLS ozone stratospheric data between 150 and 3 hPa agree well with ozonesonde measurements, within 8% for the global average. MLS values at 215 hPa are biased high compared to ozonesondes by ∼20% at middle to high latitude, although there is a lot of variability in this altitude region. Comparisons between MLS and ground-based lidar measurements from Mauna Loa, Hawaii, from the Table Mountain Facility, California, and from the Observatoire de Haute- Provence, France, give very good agreement, within ∼5%, for the stratospheric values. The comparisons between MLS and the Table Mountain Facility tropospheric ozone lidar show that MLS data are biased high by ∼30% at 215 hPa, consistent with that indicated by the ozonesonde data. We obtain better global average agreement between MLS and ozonesonde partial column values down to 215 hPa, although the average MLS values at low to middle latitudes are higher than the ozonesonde values by up to a few percent. MLS v2.2 ozone data agree better than the MLS v1.5 data with ozonesonde and lidar measurements. MLS tropical data show the wave one longitudinal pattern in the upper troposphere, with similarities to the average distribution from ozonesondes. High upper tropospheric ozone values are also observed by MLS in the tropical Pacific from June to November. Copyright 2007 by the American Geophysical Union.
  • M. R. Schoeberl, J. R. Ziemke, B. Bojkov, N. Livesey, B. Duncan, S. Strahan, L. Froidevaux, S. Kulawik, P. K. Bhartia, S. Chandra, P. F. Levelt, J. C. Witte, A. M. Thompson, E. Cuevas, A. Redondas, D. W. Tarasick, J. Davies, G. Bodeker, G. Hansen, B. J. Johnson, S. J. Oltmans, H. Vömel, M. Allaart, H. Kelder, M. Newchurch, S. Godin-Beekmann, G. Ancellet, H. Claude, S. B. Andersen, E. Kyrö, M. Parrondos, M. Yela, G. Zablocki, D. Moore, H. Dier, P. von der Gathen, P. Viatte, R. Stübi, B. Calpini, P. Skrivankova, V. Dorokhov, H. de Backer, F. J. Schmidlin, G. Coetzee, M. Fujiwara, V. Thouret, F. Posny, G. Morris, J. Merrill, C. P. Leong, G. Koenig-Langlo, E. Joseph
    Journal of Geophysical Research Atmospheres 112 24 2007年12月27日 [査読有り][通常論文]
     
    We estimate the tropospheric column ozone using a forward trajectory model to increase the horizontal resolution of the Aura Microwave Limb Sounder (MLS) derived stratospheric column ozone. Subtracting the MLS stratospheric column from Ozone Monitoring Instrument total column measurements gives the trajectory enhanced tropospheric ozone residual (TTOR). Because of different tropopause definitions, we validate the basic residual technique by computing the 200-hPa-to-surface column and comparing it to the same product from ozonesondes and Tropospheric Emission Spectrometer measurements. Comparisons show good agreement in the tropics and reasonable agreement at middle latitudes, but there is a persistent low bias in the TTOR that may be due to a slight high bias in MLS stratospheric column. With the improved stratospheric column resolution, we note a strong correlation of extratropical tropospheric ozone column anomalies with probable troposphere-stratosphere exchange events or folds. The folds can be identified by their colocation with strong horizontal tropopause gradients. TTOR anomalies due to folds may be mistaken for pollution events since folds often occur in the Atlantic and Pacific pollution corridors. We also compare the 200-hPa-to-surface column with Global Modeling Initiative chemical model estimates of the same quantity. While the tropical comparisons are good, we note that chemical model variations in 200-hPa-to-surface column at middle latitudes are much smaller than seen in the TTOR. Copyright 2007 by the American Geophysical Union.
  • J. P.F. Fortuin, C. R. Becker, M. Fujiwara, F. Immler, H. M. Kelder, M. P. Scheele, O. Schrems, G. H.L. Verver
    Journal of Geophysical Research Atmospheres 112 9 2007年05月16日 [査読有り][通常論文]
     
    The Intertropical Convergence Zone (ITCZ) passes twice a year over tropical Suriname, bringing two wet and two dry seasons. During a pilot study campaign in Suriname, cirrus clouds were observed with a mobile aerosol Raman lidar (MARL) and with balloon sondes containing a frost point hygrometer called Snow White, over the period October-November 2004. These observations are used to study the origin of cirrus clouds and the dynamical processes that determine their transport, using European Centre for Medium-Range Weather Forecasts (ECMWF) operational analyses. The height of cirrus occurrence is in phase with the height of the cold point tropopause, with maximum heights occurring during Northern Hemisphere winter that are about 2 km above the minimum values in summertime. The occurrence of cirrus often corresponds with a northerly meridional wind flow (in a layer underneath the tropopause), also when the ITCZ lies to the south in the period January-May. ECMWF analyses point out that inertial instability flow, in the form of vertically stacked meridional circulation cells in the upper troposphere (UT), can explain the transport of these cirrus events. Also evident is that radiative cooling of a moist layer transported in the UT leads to a thermal wind in the form of an easterly/westerly jet associated with the southward/northward transport of moist air. An interactive play between the inertial instability and thermal wind mechanisms explains many of the observed features of cirrus occurrence over Suriname. The observed cirrus mostly originates from the ITCZ or from deep convective centers to the south that form during the early summer monsoon. Copyright 2007 by the American Geophysical Union.
  • Franz Immler, Kirstin Krüger, Susann Tegtmeier, Masatomo Fujiwara, Paul Fortuin, Gé Verver, Otto Schrems
    Journal of Geophysical Research Atmospheres 112 3 2007年02月16日 [査読有り][通常論文]
     
    In The framework of the European Project STAR the Mobile Aerosol Raman Lidar (MARL) of the Alfred Wegener Institute (AWI) was operated in Paramaribo, Suriname (5.8°N, 55.2°W), and carried out extensive observations of tropical cirrus clouds during the local dry season from 28 September 2004 to 16 November 2004. The coverage with ice clouds was very high with 81% in the upper troposphere (above 12 km). The frequency of occurrence of subvisual clouds was found to be clearly enhanced compared to similar observations performed with the same instrument at a station in the midlatitudes. The extinction-to-backscatter ratio of thin tropical cirrus is with 26 ± 7 sr significantly higher than that of midlatitude cirrus (16 ± 9 sr). Subvisual cirrus clouds often occur in the tropical tropopause layer (TTL) above an upper tropospheric inversion. Our observations show that the ice-forming ability of the TTL is very high. The transport of air in this layer was investigated by means of a newly developed trajectory model. We found that the occurrence of clouds is highly correlated with the temperature and humidity history of the corresponding air parcel. Air that experienced a temperature minimum before the measurement took place was generally cloud free, while air that was at its temperature minimum during the observation and thus was saturated contained ice. We also detected extremely thin cloud layers slightly above the temperature minimum in subsaturated air. The solid particles of such clouds are likely to consist of nitric acid trihydrate (NAT) rather than ice. Copyright 2007 by the American Geophysical Union.
  • Takashi Shibata, Holger Vömel, Saipul Hamdi, Sri Kaloka, Fumio Hasebe, Masatomo Fujiwara, Masato Shiotani
    Journal of Geophysical Research Atmospheres 112 3 2007年02月16日 [査読有り][通常論文]
     
    Simultaneous vertical profiles of cirrus cloud backscattering and frost point temperature were obtained for the first time in the tropopause region over Bandung, Indonesia, (6.9°S, 107.62*E). These profiles were measured by ground-based lidar and by balloon-borne Cryogenic Frost point Hygrometer (CFH) sondes. Supersaturation up to several ten percent was observed by the CFH just below the cold point tropopause at the altitude where a cirrus cloud was observed by lidar. The water vapor mixing ratio decreased slightly at the altitude of the cirrus cloud, suggesting that this decrease was caused by uptake in the cirrus cloud and that the water vapor reduction corresponds to the lower limit of the cloud water content of the observed cirrus cloud. Theoretical calculations of the scattering parameters for the observed cirrus cloud particles and estimations of the time constants for sedimentation and for condensational growth indicate that particles size range is between 4 μm and 30 μm. Copyright 2007 by the American Geophysical Union.
  • F. Hasebe, M. Fujiwara, N. Nishi, M. Shiotani, H. Voemel, S. Oltmans, H. Takashima, S. Saraspriya, N. Komala, Y. Inai
    ATMOSPHERIC CHEMISTRY AND PHYSICS 7 803 - 813 2007年02月 [査読有り][通常論文]
     
    Water vapor observations by chilled-mirror hygrometers were conducted at Bandung, Indonesia (6.90 degrees S, 107.60 degrees E) and Tarawa, Kiribati (1.35 degrees N, 172.91 degrees E) in December 2003 to examine the efficiency of dehydration during horizontal advection in the tropical tropopause layer (TTL). Trajectory analyses based on bundles of isentropic trajectories suggest that the modification of air parcels' identity due to irreversible mixing by the branching-out and merging-in of nearby trajectories is found to be an important factor, in addition to the routes air parcels follow, for interpreting the water vapor concentrations observed by chilled-mirror frostpoint hygrometers in the TTL. Clear correspondence between the observed water vapor concentration and the estimated temperature history of air parcels is found showing that drier air parcels were exposed to lower temperatures than were more humid ones during advection. Although the number of observations is quite limited, the water content in the observed air parcels on many occasions was more than that expected from the minimum saturation mixing ratio during horizontal advection prior to sonde observations.
  • Ge Verver, Masatomo Fujiwara, Pier Dolmans, Cor Becker, Paul Fortuin, Larry Miloshevich
    JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 23 11 1506 - 1518 2006年11月 [査読有り][通常論文]
     
    In climate research there is a strong need for accurate observations of water vapor in the upper atmosphere. Radiosoundings provide relative humidity profiles but the accuracy of many routine instruments is notoriously inadequate in the cold upper troposphere. In this study results from a soundings program executed in Paramaribo, Suriname (5.8 degrees N, 55.2 degrees W), are presented. The aim of this program was to compare the performance of different humidity sensors in the upper troposphere in the Tropics and to test different bias corrections suggested in the literature. The payload of each sounding consisted of a chilled-mirror "Snow White" sensor from Meteolabor AG, which was used as a reference, and two additional sensors from Vaisala, that is, either the RS80A, the RS80H, or the RS90. In total 37 separate soundings were made. For the RS80A a clear, dry bias of between -4% and -8% RH is found in the lower troposphere compared to the Snow White observation, confirming the findings in previous studies. A mean dry bias was found in the upper troposphere, which could be effectively corrected. The RS80H sensor shows a significant wet bias of 2%-5% in RH in the middle and upper troposphere, which has not been reported before. Comparing observations with RS80H sensors of different ages gives no indication of sensor aging or sensor contamination. It is therefore concluded that the plastic cover introduced by Vaisala to avoid sensor contamination is effective. Finally, the RS90 sensor yields a small but significant wet bias of 2%-3% below 7-km altitude. The time-lag error correction from Miloshevich et al. was applied to the Vaisala data, which resulted in an increased variability in the relative humidity profile above 9- (RS80A), 8- (RS80H), and 11-km (RS90) altitude, respectively, which is in better agreement with the Snow White data. The averaged Snow White profile is compared with the average profiles of relative humidity from the European Centre for Medium-Range Weather Forecasts (ECMWF). No significant bias is found in either the analyses or the forecasts. The correlation coefficient for the Snow White and ECMWF data between 200 and 800 hPa was 0.66 for the 36-h forecast and 0.77 for the analysis.
  • NM Gavrilov, S Fukao, H Hashiguchi, K Kita, K Sato, Y Tomikawa, M Fujiwara
    GEOPHYSICAL RESEARCH LETTERS 33 9 2006年05月 [査読有り][通常論文]
     
    Turbulent diffusivity and turbulent ozone fluxes in the tropo-stratosphere are studied employing simultaneous observations with the Middle and Upper ( MU) Atmosphere radar and ozonesondes in Shigaraki, Japan during April 16 - 24, 1998. A broad region around the tropopause was dynamically active. Maxima of turbulent diffusivity were observed at 8 - 14 km altitude. Such maxima may produce vertical turbulent ozone fluxes across the tropopause with magnitudes comparable to those required for the global ozone budget. Mesometeorological ozone intrusions may enhance the fluxes.
  • Y. Yokouchi, F. Hasebe, M. Fujiwara, H. Takashima, M. Shiotani, N. Nishi, Y. Kanaya, S. Hashimoto, P. Fraser, D. Toom-Sauntry, H. Mukai, Y. Nojiri
    Journal of Geophysical Research Atmospheres 110 23 1 - 9 2005年12月16日 [査読有り][通常論文]
     
    Bromoform (CHBr< inf> 3< /inf> ), dibromochloromethane (CHBr< inf> 2< /inf> Cl), and dibromomethane (CH< inf> 2< /inf> Br< inf> 2< /inf> ) in the atmosphere were measured at various sites, including tropical islands, the Arctic, and the open Pacific Ocean. Up to 40 ppt of bromoform was observed along the coasts of tropical islands under a sea breeze. Polybromomethane concentrations were highly correlated among the coastal samples, and the ratios CH< inf> 2< /inf> Br< inf> 2< /inf> /CHBr< inf> 3< /inf> and CHBr< inf> 2< /inf> Cl/CHBr< inf> 3< /inf> showed a clear tendency to decrease with increasing CHBr< inf> 3< /inf> concentration. These findings are consistent with the observations that polybromomethanes are emitted mostly from macroalgae whose growth is highly localized to coastal areas and that CHBr< inf> 3< /inf> has the shortest lifetime among these three compounds. The relationship between the concentration ratios CHBr< inf> 3< /inf> /CH< inf> 2< /inf> Br< inf> 2< /inf> and CHBr< inf> 2< /inf> Cl/CH< inf> 2< /inf> Br< inf> 2< /inf> suggested a large mixing/dilution effect on bromomethane ratios in coastal regions and yielded a rough estimate of 9 for the molar emission ratio of CHBr< inf> 3< /inf> / CH< inf> 2< /inf> Br< inf> 2< /inf> and of 0.7 for that of CHBr< inf> 2< /inf> Cl/CH< inf> 2< /inf> Br< inf> 2< /inf> . Using these ratios and an global emission estimate for CH< inf> 2< /inf> Br< inf> 2< /inf> (61 Gg/yr (Br)) calculated from its background concentration, the global emission rates of CHBr< inf> 3< /inf> and CHBr< inf> 2< /inf> Cl were calculated to be approximately 820(±310) Gg/yr (Br) and 43 (±16) Gg/yr (Br), respectively, assuming that the bromomethanes ratios measured in this study are global representative. The estimated CHBr< inf> 3< /inf> emission is consistent with that estimated in a very recent study by integrating the sea-to-air flux database. Thus the contribution of CHBr< inf> 3< /inf> and CHBr< inf> 2< /inf> Cl to inorganic Br in the atmosphere is likely to be more important than previously thought. Copyright 2005 by the American Geophysical Union.
  • M. Venkat Ratnam, T. Tsuda, M. Shiotani, M. Fujiwara
    SOLA 1 185 - 188 2005年 [査読有り][通常論文]
     
    Structure and variability of the tropical tropopause are presented using radio occultation measurements by CHAMP/GPS (CHAllenging Mini satellite Payload/Global Positioning System) from May 2001 to December 2004 (with a total of 175,149 occultations). The tropopause heights defined by both lapse rate and cold point generally show large-scale, off-equatorial maxima (tropopause increase at 20 degrees N or S than at equator), and sometimes even a high tropopause for about 0.3 to 0.65 km (on an average) at 20 degrees N and S simultaneously than at the equator along a particular meridian, in contrast to our previous knowledge. Although this feature has already been reported partially during the summer monsoon season, the present study shows the seasonal and geographical distributions of the tropical tropopause comprehensively using a new promising observational technique. In addition, the vertical shape of the tropopause is found to be sharp in the equatorial region and broad in the subtropics especially in northern winter. Possible mechanisms are discussed in light of dynamical and radiative processes.
  • A Gettelman, PMD Forster, M Fujiwara, Q Fu, H Vomel, LK Gohar, C Johanson, M Ammerman
    JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 109 D7 2004年04月 [査読有り][通常論文]
     
    [1] The radiation balance of the tropical tropopause layer (TTL) is examined using several different radiation codes with standard profiles compiled from observations in the tropics assuming clear sky conditions. These codes include detailed radiative transfer models and simplified codes for global climate models. The importance of the various radiatively active gases are examined. Water vapor is the most important contributor to the TTL radiation balance, but carbon dioxide and ozone also play a role. Differences in radiative heating between radiation models are mostly due to treatments of shortwave radiation. Differences between models below the TTL are due to different treatments of water vapor continuum absorption. The level of zero clear sky radiative heating, a level important for understanding the transport of air into the stratosphere, is generally found near 15 km, 125 hPa and 200 degreesK ( 360 K potential temperature), consistent with previous work. Changes in time and space can modify this level by +/- 500 m, and individual profiles vary from these averages by +/- 400 m (1sigma). Increases in water vapor in the TTL would tend to increase the altitude of the level at which the net heating is zero, while increases in carbon dioxide or ozone would tend to decrease this level. Clouds in the TTL tend to increase the level due to enhancements in longwave cooling above clouds. The implications for transport are discussed.
  • M Fujiwara, SP Xie, M Shiotani, H Hashizume, F Hasebe, H Vomel, SJ Oltmans, T Watanabe
    JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 108 D24 2003年12月 [査読有り][通常論文]
     
    Shipboard radiosonde measurements revealed a persistent temperature inversion layer with a thickness of similar to200 m at 12-13 km in a nonconvective region over the tropical eastern Pacific, along 2degreesN, in September 1999. Simultaneous relative humidity measurements indicated that the thin inversion layer was located at the top of a very wet layer with a thickness of 3-4 km, which was found to originate from the intertropical convergence zone (ITCZ) to the north. Radiative transfer calculations suggested that this upper tropospheric inversion (UTI) was produced and maintained by strong longwave cooling in this wet layer. A strong easterly jet stream was also observed at 12-13 km, centered around 4degrees-5degreesN. This easterly jet was in the thermal wind balance, with meridional temperature gradients produced by the cloud and radiative processes in the ITCZ and the wet outflow. Furthermore, the jet, in turn, acted to spread inversions further downstream through the transport of radiatively active water vapor. This feedback mechanism may explain the omnipresence of temperature inversions and layering structures in trace gases in the tropical troposphere. Examination of high-resolution radiosonde data at other sites in the tropical Pacific indicates that similar UTIs often appear around 12-15 km. The UTI around 12-15 km may thus be characterized as one of the "climatological" inversions in the tropical troposphere, forming the lower boundary of the so-called tropical tropopause layer, where the tropospheric air is processed photochemically and microphysically before entering the stratosphere.
  • H Vomel, M Fujiwara, M Shiotani, F Hasebe, SJ Oltmans, JE Barnes
    JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 20 11 1560 - 1567 2003年11月 [査読有り][通常論文]
     
    The Snow White hygrometer, made by Meteolabor AG, Switzerland, is a new chilled-mirror instrument using a thermoelectric Peltier cooler to measure atmospheric water vapor. Its performance under dry conditions is evaluated in simultaneous measurements using the NOAA/CMDL frost-point hygrometer at Boulder, Colorado; San Cristobal, Galapagos Islands, Ecuador; Watukosek, Indonesia; and Mauna Loa Observatory, Hawaii. The Snow White exhibits a lower detection limit of about 3%-6% relative humidity, depending on the sensor configuration. This detection limit is determined by the temperature depression attainable by the thermoelectric cooler. In some cases, loss of frost-point control within layers with relative humidity below this detection limit caused inaccurate measurements above these dry layers, where the relative humidity was within the detection range of the instrument. The sensor does not operate in the stratosphere because of the large frost-point depression and the large potential for outgassing of water from the instrument box and the sensor housing. The instrument has some capabilities in the tropical tropopause region; however, the results are somewhat mixed.
  • M Fujiwara, M Shiotani, F Hasebe, H Vomel, SJ Oltmans, PW Ruppert, T Horinouchi, T Tsuda
    JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 20 11 1534 - 1542 2003年11月 [査読有り][通常論文]
     
    The "Snow White'' hygrometer is a low-cost, chilled-mirror hygrometer for radiosonde applications provided by a Swiss company, Meteolabor AG. A total of 54 Snow White soundings were conducted at five tropical stations in different seasons in 2000-01. All soundings were made with Vaisala RS80 radiosondes equipped either with the A-Humicap (22 soundings) or H-Humicap (32) relative humidity (RH) sensor. Comparisons of the RH with respect to liquid water between the Snow White and the different RS80 Humicap sensors are made. The Snow White measurements show reasonable agreement with the H-Humicap measurements from the surface up to similar to12 km (above -50degreesC air temperature), the region where the H-Humicap sensor can be considered reliable. Above 12 km, the H-Humicap sensor tends to miss small vertical-scale structures in RH due to the time lag error, but on average both instruments show no significant difference up to 14 km(-65degreesC). The comparison between the Snow White and A-Humicap sensors shows the known A-Humicap dry bias error at low temperatures and second dry bias error in the wet lower troposphere. The latter error [(A-Humicap RH)similar or equal to0.93 (Snow White RH) above 50% RH] may be a common problem for the recent A-Humicap sensors. These intercomparisons confirm the validity of the Snow White measurements at least up to the tropical upper troposphere and above 3%-6% RH.
  • MK Yamamoto, M Fujiwara, T Horinouchi, H Hashiguchi, S Fukao
    GEOPHYSICAL RESEARCH LETTERS 30 9 2003年05月 [査読有り][通常論文]
     
    [1] In November 2001, the Equatorial Atmosphere Radar (0.20degreesS, 100.32degreesE) observed a continuous strong eastward wind shear (10-50 m s(-1) km(-1)), westward wind (2-27 m s(-1)), and the radar echo layer tilted downward to the west in the region 0-1 km above the tropopause. During the same period, the Richardson number calculated with hourly-averaged horizontal wind and radiosonde temperature data was almost continuously <0.5 and sometimes <0.25, which seems to indicate that the Kelvin-Helmholtz instability (KHI) frequently occurs in that region. The existence of the tilted radar echo layer can be explained by KHI billows. A spurious updraft caused by the KHI-induced tilted echo layer and by the strong westward wind was also observed in the region.
  • M Fujiwara, MK Yamamoto, H Hashiguchi, T Horinouchi, S Fukao
    GEOPHYSICAL RESEARCH LETTERS 30 4 2003年02月 [査読有り][通常論文]
     
    The Equatorial Atmosphere Radar ( EAR) installed in Sumatra Island, Indonesia, observed significant enhancement of turbulence in the tropopause region, 15-17 km, intermittently for similar to5 days in November 2001. The turbulence intensity was estimated with the spectral width of the radar echo power spectrum, and the turbulence during the period was a factor of up to similar to5 larger in kinetic energy than that in other periods. Further analyses confirm that the enhanced turbulence was convectively generated in the breaking phase of an equatorial Kelvin wave. Between July and December 2001, we observed at least three more prominent cases of the turbulence generation by breaking Kelvin waves in the tropopause region.
  • H Vomel, SJ Oltmans, BJ Johnson, F Hasebe, M Shiotani, M Fujiwara, N Nishi, M Agama, J Cornejo, F Paredes, Enriquez, II
    JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 108 D4 2003年02月 [査読有り][通常論文]
  • AM Thompson, JC Witte, SJ Oltmans, FJ Schmidlin, JA Logan, M Fujiwara, VWJH Kirchhoff, F Posny, GJR Coetzee, B Hoegger, SJ Kawakami, T Ogawa, JPF Fortuin, HM Kelder
    JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 108 D2 2003年01月 [査読有り][通常論文]
     
    The first view of stratospheric and tropospheric ozone variability in the Southern Hemisphere tropics is provided by a 3-year record of ozone soundings from the Southern Hemisphere Additional Ozonesondes (SHADOZ) network (http://croc.gsfc.nasa.gov/shadoz). Observations covering 1998-2000 were made over Ascension Island, Nairobi ( Kenya), Irene ( South Africa), Reunion Island, Watukosek (Java), Fiji, Tahiti, American Samoa, San Cristobal (Galapagos), and Natal (Brazil). Total, stratospheric, and tropospheric column ozone amounts usually peak between August and November. Other features are a persistent zonal wave-one pattern in total column ozone and signatures of the quasi-biennial oscillation (QBO) in stratospheric ozone. The wave-one is due to a greater concentration of free tropospheric ozone over the tropical Atlantic than the Pacific and appears to be associated with tropical general circulation and seasonal pollution from biomass burning. Tropospheric ozone over the Indian and Pacific Oceans displays influences of the waning 1997-1998 El Nino, seasonal convection, and pollution transport from Africa. The most distinctive feature of SHADOZ tropospheric ozone is variability in the data, e. g., a factor of 3 in column amount at 8 of 10 stations. Seasonal and monthly means may not be robust quantities because statistics are frequently not Gaussian even at sites that are always in tropical air. Models and satellite retrievals should be evaluated on their capability for reproducing tropospheric variability and fine structure. A 1999 2000 ozone record from Paramaribo, Surinam (6degreesN, 55degreesW) (also in SHADOZ) shows a marked contrast to southern tropical ozone because Surinam is often north of the Intertropical Convergence Zone (ITCZ). A more representative tropospheric ozone climatology for models and satellite retrievals requires additional Northern Hemisphere tropical data.
  • AM Thompson, JC Witte, RD McPeters, SJ Oltmans, FJ Schmidlin, JA Logan, M Fujiwara, VWJH Kirchhoff, F Posny, GJR Coetzee, B Hoegger, S Kawakami, T Ogawa, BJ Johnson, H Vomel, G Labow
    JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 108 D2 2003年01月 [査読有り][通常論文]
     
    A network of 10 southern hemisphere tropical and subtropical stations, designated the Southern Hemisphere Additional Ozonesondes (SHADOZ) project and established from operational sites, provided over 1000 ozone profiles during the period 1998-2000. Balloon-borne electrochemical concentration cell (ECC) ozonesondes, combined with standard radiosondes for pressure, temperature, and relative humidity measurements, collected profiles in the troposphere and lower to midstratosphere at: Ascension Island; Nairobi, Kenya; Irene, South Africa; Reunion Island; Watukosek, Java; Fiji; Tahiti; American Samoa; San Cristobal, Galapagos; and Natal, Brazil. The archived data are available at: <http://croc.gsfc.nasa.gov/shadoz>. In this paper, uncertainties and accuracies within the SHADOZ ozone data set are evaluated by analyzing: (1) imprecisions in profiles and in methods of extrapolating ozone above balloon burst; (2) comparisons of column-integrated total ozone from sondes with total ozone from the Earth-Probe/Total Ozone Mapping Spectrometer ( TOMS) satellite and ground-based instruments; and (3) possible biases from station to station due to variations in ozonesonde characteristics. The key results are the following: (1) Ozonesonde precision is 5%. (2) Integrated total ozone column amounts from the sondes are usually to within 5% of independent measurements from ground-based instruments at five SHADOZ sites and overpass measurements from the TOMS satellite (version 7 data). (3) Systematic variations in TOMS-sonde offsets and in ground-based-sonde offsets from station to station reflect biases in sonde technique as well as in satellite retrieval. Discrepancies are present in both stratospheric and tropospheric ozone. (4) There is evidence for a zonal wave-one pattern in total and tropospheric ozone, but not in stratospheric ozone.
  • M Fujiwara, Y Tomikawa, K Kita, Y Kondo, N Komala, S Saraspriya, T Manik, A Suripto, S Kawakami, T Ogawa, E Kelana, B Suhardi, SWB Harijono, M Kudsy, T Sribimawati, MD Yamanaka
    ATMOSPHERIC ENVIRONMENT 37 3 353 - 362 2003年01月 [査読有り][通常論文]
     
    Ozonesonde observation campaigns were conducted over the Indonesian maritime continent in September-October 1998 and in August-September 1999. Three stations were used for each campaign, Watukosek (7.5degreesS, 112.6degreesE), Kototabang (0.20degreesS, 100.3degreesE), and Pontianak (0.03degreesN, 109.3degreesE) for the 1998 campaign, and Watukosek, Kototabang, and Darwin (12.25degreesS, 130.55degreesE) for the 1999 campaign. Both periods were basically characterized as the La Nina period, and the tropospheric ozone concentrations showed normal values. Temporal variation and horizontal distribution of an ozone layered structure with a 1-1.5-km thickness were obtained just below the tropopause at the two equatorial stations during the 1998 campaign. Meteorological data analyses including the reverse domain filling technique suggested that the most plausible explanation for the layer is the quasi-horizontal, thin intrusion from the northern midlatitude lower stratosphere associated with a breaking Rossby wave and large-scale flow pattern. (C) 2002 Elsevier Science Ltd. All rights reserved.
  • H Hashizume, SP Xie, M Fujiwara, M Shiotani, T Watanabe, Y Tanimoto, WT Liu, K Takeuchi
    JOURNAL OF CLIMATE 15 23 3379 - 3393 2002年12月 [査読有り][通常論文]
     
    Tropical instability waves (TIWs), with a typical wavelength of 1000 km and period of 30 days, cause the equatorial front to meander and result in SST variations on the order of 1degrees-2degreesC. Vertical soundings of temperature, humidity, and wind velocity were obtained on board a Japanese research vessel, which sailed through three fully developed SST waves from 140degrees to 110degreesW along 2degreesN during 21-28 September 1999. A strong temperature inversion is observed throughout the cruise along 2degreesN, capping the planetary boundary layer (PBL) that is 1-1.5 km deep. Temperature response to TIW-induced SST changes penetrates the whole depth of the PBL. In response to an SST increase, air temperature rises in the lowest kilometer and shows a strong cooling at the mean inversion height. As a result, this temperature dipole is associated with little TIW signal in the observed sea level pressure (SLP). The cruise mean vertical profiles show a speed maximum at 400-500 m for both zonal and meridional velocities. SST-based composite profiles of zonal wind velocity show weakened ( intensified) vertical shear within the PBL that is consistent with enhanced ( reduced) vertical mixing, causing surface wind to accelerate ( decelerate) over warm (cold) SSTs. Taken together, the temperature and wind soundings indicate the dominance of the vertical mixing over the SLP-driving mechanism. Based on the authors' measurements, a physical interpretation of the widely used PBL model proposed by Lindzen and Nigam is presented.
  • M Shiotani, M Fujiwara, F Hasebe, H Hashizume, H Vomel, SJ Oltmans, T Watanabe
    JOURNAL OF THE METEOROLOGICAL SOCIETY OF JAPAN 80 4B 897 - 909 2002年09月 [査読有り][通常論文]
     
    We have conducted GPS radiosonde and ozonesonde observations on board the research vessel "Shoyo-Maru" in the equatorial eastern Pacific. These observations took place in September and October 1999 as a part of the Soundings of Ozone and Water in the Equatorial Region (SOWER)/Pacific mission. The mean profile of ozone is similar to that for the dry season (September to October) at San Cristobal, Galapagos (0.9degreesS, 89.6degreesW) located in the equatorial eastern Pacific. The mean tropospheric ozone concentration is about 40 ppbv with a maximum in the mid-troposphere. Compared with the mean profile during the dry season at Watukosek,. Indonesia (7.5degreesS, 112.6degreesE), this mid-tropospheric maximum is larger, and a sharp increase of ozone below the tropopause begins at a lower altitude for the Shoyo-Maru profile. We frequently observed layers in which ozone and humidity are highly anti-correlated. These layers have vertical scales from several kilometers to several hundred meters. Horizontal scales of these layers are roughly 1000 km, which may correspond to time scales of about 2 days, since the vessel sailed about 500 km/day. These layers are related to northerly winds, which bring in wet and ozone-poor air from the inter-tropical convergence zone situated in the northern side of the main cruise track. Similar layers were observed in ozone profiles at San Cristobal and Watukosek, mostly during the dry season, suggesting the existence of layers advected without vertical mixing.
  • H Vomel, SJ Oltmans, BJ Johnson, F Hasebe, M Shiotani, M Fujiwara, N Nishi, M Agama, J Cornejo, F Paredes, H Enriquez
    JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 107 D14 2002年07月 [査読有り][通常論文]
     
    [1] Balloon-borne observations of frost-point temperature and ozone in the equatorial western, central and eastern Pacific as well as over equatorial eastern Brazil provide a highly accurate data set of water vapor across the tropical tropopause. Data were obtained at San Cristobal, Galapagos, Ecuador (0.9degreesS, 89.6degreesW), during the late northern winter and the late northern summer in 1998 and 1999 and at Juazeiro do Norte, Brazil (7.2degreesS, 39.3degreesW), in February and November 1997. Earlier data in the western Pacific region in March 1993 were reanalyzed to extend the scope of the observations. The data show three different circumstances in which saturation or supersaturation occurs and imply different mechanisms for dehydration at the tropical tropopause: (1) convective dehydration, (2) slow-ascent dehydration, and (3) large-scale wave-driven dehydration. Furthermore, air that crosses the tropical tropopause in the late northern summer may be dehydrated further during late northern fall, as the average tropical tropopause rises and cools. Not all soundings show dehydration, and there are clear differences in the frequency and depth of saturation in different regions and seasons. The tropopause transition region can be identified in accurate measurements of relative humidity, even under conditions where ozone observations are ambiguous. Deep convection plays an important role in setting up this transition region, which is then subject to large-scale wave activity and wave breaking at the tropopause or midlatitude intrusions. High relative humidities over regions of strong subsidence show that descending motion in the troposphere is limited to levels below the transition region.
  • F Murata, MD Yamanaka, M Fujiwara, SY Ogino, H Hashiguchi, S Fukao, M Kudsy, T Sribiawati, SWB Harijono, E Kelana
    JOURNAL OF THE METEOROLOGICAL SOCIETY OF JAPAN 80 3 347 - 360 2002年06月 [査読有り][通常論文]
     
    Simultaneous observations with a UHF-band boundary layer radar (hereafter referred as BLR), GPS rawinsondes and a tipping-bucket-type rain gauge were conducted at Kototabang (0.20degreesS, 100.32degreesE, 865 m MSL), which is located on the mountainous region near Bukittinggi, West Sumatera Province, during 27 September-7 October 1998 (rainy season). Low-level (1-3 km) westerly wind stronger than 10 m/s was observed, and precipitation tended to occur when the low-level westerly wind became weak (2-5 October). Similar relationship was observed for two months (1 September-31 October 1998) during which only BLR and surface meteorological instruments were operated at Kototabang. NCEP/NCAR objective analysis, and GMS T-BB data showed that the low-level (850 hPa) wind field, and cloud distribution, were both completely different between the Indonesian Archipelago (east of Kototabang) and the eastern Indian Ocean-including the Bay of Bengal (west of Kototabang)-during the analysis period. Two large-scale cloud disturbances existed along the equator in the western side (80degrees-100degreesE), but precipitation at Kototabang did not correspond to these cloud disturbances. The implication is that effects of the mountain range of Sumatera blocked the large-scale cloud disturbances over the Indian Ocean. The precipitation by local-scale cloud systems prevailed at Kototabang. The convergences of local circulations, which are generally dominant under weak background winds, are considered as the major cause of local-scale cloud systems.
  • Y Tomikawa, K Sato, K Kita, M Fujiwara, M Yamamori, T Sano
    JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 107 D10 2002年05月 [査読有り][通常論文]
     
    [1] An intensive observation with ozonesondes, radiosondes, and the Middle and Upper atmosphere (MU) radar was conducted at Shigaraki (34.9degreesN, 136.1degreesE), Japan, from 16 through 24 April 1998 to investigate the formation mechanism of ozone laminae in the midlatitude lower stratosphere. In these observations the temporal variation of an ozone lamina at Shigaraki was continuously observed through a short time interval of 8 hours. During the observation period an ozone lamina with a thickness of 2-3 km appeared and ascended with a speed of similar to1 km day(-1) in the height region of 18-21 km. It is deduced that inertia gravity waves existing in this height region did not contribute to formation of the ozone lamina, because their amplitudes were too small and their vertical phase propagation was in the opposite direction. The reverse domain filling method was used to reconstruct the "high-resolution'' modified potential vorticity field using backward trajectory calculations. The results indicate that this ozone lamina was caused by differential advection due to the vertical shear associated with the subtropical westerly jet and embedded stationary Rossby wave therein. This means that large-scale motions concurrent with vertical wind shear can produce much smaller-scale structures in material fields than those of the large-scale motions themselves.
  • M Fujiwara, M Takahashi
    JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 106 D19 22763 - 22780 2001年10月 [査読有り][通常論文]
     
    Large-scale disturbances which cause the variations of ozone and water around the equatorial tropopause axe investigated with a general circulation model incorporating a simplified ozone photochemistry, realistic topography, and seasonal cycle of the sea surface temperature. Eastward moving large-scale equatorial gravity waves are found to be dominant to modulate the minor constituents' distribution around the equatorial tropopause. A case over the Indian Ocean in the northern summer was investigated in detail. The disturbance had the characteristics of the equatorial Kelvin wave at the tropopause level, coupled with organized active convections in the troposphere. Associated with the downward displacement (and suppressed-convection) phase of this system, dry, ozone-rich stratospheric air moved downward into the upper troposphere. At the opposite phase, physical and dynamical processes above the organized active convections prevented the lower stratosphere from accumulating excess water. Thus the dryness around the equatorial tropopause is maintained during the passage of such a system. Analysis of 4-year integration data reveals that such disturbances axe especially active over the Indian Ocean during the northern summer through autumn. This is probably related to the development of the summer monsoon circulation over south Asia. This model has also simulated the zonal wave one structure of tropical tropospheric ozone and suggested the important contribution of convective transport to the structure.
  • M Fujiwara, F Hasebe, M Shiotani, N Nishi, H Vomel, SJ Oltmans
    GEOPHYSICAL RESEARCH LETTERS 28 16 3143 - 3146 2001年08月 [査読有り][通常論文]
     
    Soundings of frost-point hygrometers, ozonesondes, and radiosondes at San Cristobal Island (0.9 degreesS, 89.6 degreesW) in September 1998 provide an observational evidence that equatorial Kelvin waves around the tropopause act as a dehydration pump for the stratosphere. During the downward-displacement phase of a Kelvin wave, dry and ozone-rich stratospheric air is transported into the upper troposphere. During the upward-displacement phase, on the other hand, higher specific-humidity air moves up in the tropopause region, but at the same time, this upward motion causes cooling of the air that limits the water vapor amount entering the stratosphere. Also, wave breaking contributes to the irreversible transport of ozone across the tropopause. Considering their omnipresence at the equatorial tropopause, we suggest that Kelvin waves may be one of the important agents for maintaining the dryness of the tropical lower stratosphere.
  • AM Thompson, JC Witte, RD Hudson, H Guo, Herman, JR, M Fujiwara
    SCIENCE 291 5511 2128 - 2132 2001年03月 [査読有り][通常論文]
     
    New methods for retrieving tropospheric ozone column depth and absorbing aerosol (smoke and dust) from the Earth Probe-Total Ozone Mapping Spectrometer (EP/TOMS) are used to follow pollution and to determine interannual variability and trends. During intense fires over Indonesia (August to November 1997), ozone plumes, decoupled from the smoke below, extended as far as India, This ozone overlay a regional ozone increase triggered by atmospheric responses to the El Nino and Indian Ocean Dipole. Tropospheric ozone and smoke aerosol measurements from the Nimbus 7 TOMS instrument show El Nino signals but no tropospheric ozone trend in the 1980s. Offsets between smoke and ozone seasonal maxima point to multiple factors determining tropical tropospheric ozone variability.
  • Masatomo Fujiwara, Kazuyuki Kita, Toshihiro Ogawa, Shuji Kawakami, Takuki Sano, Ninong Komala, Slamet Saraspriya, Agus Suripto
    Journal of Geophysical Research Atmospheres 105 2 1879 - 1888 2000年 [査読有り][通常論文]
     
    Regular ozonesonde observation and total ozone observation with the Brewer spectrophotometer have been conducted at Watukosek (7.5°S, 112.6°E), Indonesia, since 1993. Three seasons are recognized for the vertical distribution of tropospheric ozone. (1) During the local wet season, between December and March, the ozone mixing ratio is nearly constant at 25 ppbv throughout the troposphere. (2) During the transition season from wet to dry, between April and July, the mixing ratio is often enhanced in the uppermost troposphere. (3) During the local dry season, between August and November, the concentration is enhanced in the planetary boundary layer, and extensive forest fires in Indonesia associated with the strong El Niño events of 1994 and of 1997 have enhanced the ozone mixing ratio in the middle troposphere, the integrated tropospheric ozone, and the total ozone at Watukosek. Copyright 2000 by the American Geophysical Union.
  • Ozonesonde observations in Indonesia during the BIBLE-A period
    M. Fujiwara, K. Kita, S. Kawakami, T. Ogawa, S. Saraspriya, T. Manik, A. Suripto, N. Komala, E. Kelana, T. Sribimawati, M. Kudsy, S. W, B. Harijono, M. D. Yamanaka
    Proceedings of Quadrennial Ozone Symposium Sapporo 2000 389-390  2000年 [査読無し][通常論文]
  • Ozone-increased layers in the free troposphere observed over Indonesia and Northern Australia in BIBLE-A and B aircraft observation campaigns
    Y. Higashi, K. Kita, Y. Miyazaki, Y. Tomikawa, M. Fujiwara, S. Kawakami, T. Shirai, N. Nishi, Y. Kondo, D. Blake, B. Liley, N. Komala, S. Saraspriya, A. Suripto, M. Timbul, T. Ogawa
    Proceedings of the Quadrennial ozone symposium Sapporo 2000 427-428  2000年 [査読無し][通常論文]
  • Observation and origin of dry sir with high mixing ratios of ozone and its precursor gases in the tropical and subtropical upper troposphere during BIBLE aircraft observations
    S. Kawakami, K. Kita, Y. Miyazaki, Y. Higashi, M. Fujiwara, Y. Tomikawa, N. Nishi, Y. Kondo, D. Blake, B. Liley, N. Komala, S. Saraspriya, A. Suripto, A. Shirai, T. Ogawa
    Proceedings of Quadrennial Ozone Symposium Sapporo 2000 95-96  2000年 [査読無し][通常論文]
     
    Proceedings of Quadrennial Ozone Symposium Sapporo 2000
  • K Kita, M Fujiwara, S Kawakami
    ATMOSPHERIC ENVIRONMENT 34 17 2681 - 2690 2000年 [査読有り][通常論文]
     
    Significant increases of total ozone were observed both by the total ozone mapping spectrometer (TOMS) and by the Brewer spectrophotometer in Indonesia in September and October of 1994 and 1997, during the El Nino periods, when extensive forest fires were reported in Sumatra Island, Kalimantan (the southern part of Borneo Island) and south New Guinea. The two observations were consistent with each other, and the total ozone increases were attributed to the tropospheric ozone increases because their amplitudes agreed with those of integrated tropospheric ozone increases derived from ozonesonde observations. The TOMS data indicated that the horizontal distributions and temporal variations of the ozone increases were similar in both years; the ozone increases were found mainly over Sumatra Island and the Malay Peninsula in September, and spread out from Kalimantan to the central Indian Ocean in October. This ozone distribution was partly different from the reported fire areas. This difference suggested the importance of the horizontal advection due to the easterly wind in the lower troposphere and of the vertical transport due to the upward wind at the west of Sumatra Island, in the ozone maximum area. Distinctive total ozone increases similar to those in 1994 and 1997 repeatedly appeared over the Indonesian region in the TOMS data between 1979 and 1998. The average ozone increase in this region was estimated by subtracting the background structure of total ozone in the tropics, and this analysis showed that large ozone increases mostly occurred in the dry season during the El Nino periods when the precipitation decreased significantly and extensive forest fires occurred frequently in Indonesia. (C) 2000 Elsevier Science Ltd. All rights reserved.
  • M Fujiwara, K Kita, T Ogawa, S Kawakami, T Sano, N Komala, S Saraspriya, A Suripto
    JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 105 D2 1879 - 1888 2000年01月 [査読有り][通常論文]
     
    Regular ozonesonde observation and total ozone observation with the Brewer spectrophotometer have been conducted at Watukosek (7.5 degrees S, 112.6 degrees E), Indonesia, since 1993. Three seasons are recognized for the vertical distribution of tropospheric ozone. (1) During the local wet season, between December and March, the ozone mixing ratio is nearly constant at 25 ppbv throughout the troposphere. (2) During the transition season from wet to dry, between April and July, the mixing ratio is often enhanced in the uppermost troposphere. (3) During the local dry season, between August and November, the concentration is enhanced in the planetary boundary layer, and extensive forest fires in Indonesia associated with the strong El Nino events of 1994 and of 1997 have enhanced the ozone mixing ratio in the middle troposphere, the integrated tropospheric ozone, and the total ozone at Watukosek.
  • M Fujiwara, K Kita, S Kawakami, T Ogawa, N Komala, S Saraspriya, A Suripto
    GEOPHYSICAL RESEARCH LETTERS 26 16 2417 - 2420 1999年08月 [査読有り][通常論文]
     
    Pronounced enhancements of total and tropospheric ozone were observed with the Brewer spectrophotometer and ozonesondes at Watukosek (7.5 degrees S, 112.6 degrees E), Indonesia in 1994 and in 1997 when extensive forest fires were reported in Indonesia. The integrated tropospheric ozone increased from 20 DU to 40 DU in October 1994 and to 55 DU in October 1997. On October 13, 1994, most ozone mixing ratios were more than 50 ppbv throughout the troposphere and exceeded 80 ppbv at some altitudes. On October 22, 1997, the concentrations were more than 50 ppbv throughout the troposphere and exceeded 100 ppbv at several altitudes. The coincidences of the ozone enhancements with the forest fires suggest the photochemical production of tropospheric ozone due to its precursors emitted from the fires for both cases. The years of 1994 and 1997 correspond to El Nino events when convective activity becomes low in Indonesia. Thus, in this region, it is likely that pronounced enhancements of tropospheric ozone associated with extensive forest fires due to sparse precipitation may take place with a period of a few years coinciding with El Nino events. This is in a marked contrast to the situation in South America and Africa where large-scale biomass burnings occur every year.
  • M Fujiwara, K Kita, T Ogawa
    JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 103 D15 19173 - 19182 1998年08月 [査読有り][通常論文]
     
    An intensive observation with ozonesondes and rawinsondes was conducted in Indonesia in May and June 1995 to investigate a phenomenon of ozone enhancement in the tropical upper troposphere. We obtained the characteristics of an enhancement that continued for about 20 days, concurring with a zonal wind oscillation associated with the equatorial Kelvin wave around the tropopause and the Madden-Julian oscillation (MJO) in the troposphere. The isoline of ozone mixing ratio of 40 nmol/mol moved by 5.0 km downward from 17.8 km to 12.8 km, while the tropopause height was 16.2-17.8 km throughout the period. Moreover, the maximum ozone concentration of 300 nmol/mol at the tropopause was concurrent with the maximum eastward wind phase of the Kelvin wave. The detailed mechanism of the ozone transport is interpreted as follows: The downward motion associated with the Kelvin wave and the MJO transported the stratospheric ozone into the troposphere, and the air mixing due to the Kelvin wave breaking at the tropopause also caused stratosphere-troposphere exchange. The upper limit of the net amount of ozone transported from the stratosphere was estimated to be 9.9 Dobson units with the zonal and meridional extents of the ozone-increased region of more than 6.6 x 10(6) m and 1.8 x 10(6) m, respectively, to imply the potential to affect the photochemistry around the tropical tropopause.
  • Tropospheric ozone over Pacific and Indonesian Region: Relation with ENSO activity and a preliminary report on BIBLE aircraft campaign
    K. Kita, M. Fujiwara, Y. Miyazaki, S. Kawakami, T. Ogawa, N. Komala, S. Saraspriya, Y. Kondo, M. Koike, T. Machida, B. Liley, D. Blake, M. Watanabe, N. Nishi
    Proceedings of International symposium on tropospheric ozone in East Asia and its potential impacts on vegetation 45-46  1998年 [査読無し][通常論文]

書籍

  • Masatomo Fujiwara, Gloria L. Manney, Lesley J. Gray, Jonathon S. Wright (担当:共編者(共編著者)範囲:Co-editor, Chapters 1, 2, 3, 4, 8, 9, 11, 12)
    WCRP/SPARC 2022年01月 612
  • Vömel, H, M. Fujiwara (担当:共著範囲:Chapter 46. Aerological measurements)
    edited by Thomas Foken, Springer Nature, Switzerland 2021年 1247-1280
  • 低温環境の科学事典
    河村公隆, 大島慶一郎, 小達恒夫, 川村賢二, 佐﨑元, 杉山慎, 関宰, 高橋晃周, 西岡純, 原登志彦, 福井学, 藤吉康志, 三寺史夫, 宮﨑雄三, 本山秀明, 渡部直樹 (担当:分担執筆範囲:ブリューワー-ドブソン循環(成層圏の大気大循環))
    朝倉書店 2016年
  • 第2版 地球惑星科学入門
    在田一則, 竹下徹, 見延庄士郎, 渡部重十 (担当:分担執筆範囲:第18章共同執筆)
    北海道大学出版会 2015年
  • 地球と宇宙の化学事典
    日本地球化学会 (担当:分担執筆範囲:成層圏大気の組成)
    朝倉書店 2012年
  • 地球惑星科学入門
    在田一則, 竹下徹, 見延庄士郎, 渡部重十 (担当:分担執筆範囲:第18章共同執筆)
    北海道大学出版会 2010年
  • オゾン層破壊の科学
    北海道大学大学院環境科 (担当:分担執筆範囲:序章, 1章, 5-1章, 5-2章, 終章)
    北海道大学出版会 2007年 (ISBN: 9784832981799)

講演・口頭発表等

その他活動・業績

受賞

  • 2018年 Sustainability Science 2017 Sustainability Science Best Paper Awards - Outstanding Article (Sugiyama et al., SS, 2017)
     
    受賞者: Sugiyama et
  • 2010年 日本気象学会 2010年気象集誌論文賞
     for papers by Sakazaki and Fujiwara (JMSJ, 2010a, 2010b) 
    受賞者: 坂崎 貴俊;藤原 正智
  • 2000年 日本気象学会 2000年度山本・正野論文賞
     for paper by Fujiwara et al. (JGR, 1998) 
    受賞者: 藤原 正智

教育活動情報

主要な担当授業

  • 大気海洋物理学基礎論
    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 : 気象学, 海洋学, 大気大循環, 地衡風(流), 温帯高低気圧, 熱帯気象学, 数値予報, 大気境界層, 大気化学, オゾン層, 気候変動, 地球温暖化; 熱塩循環, 風成循環, ポテンシャル渦度, 西岸境界流, 海洋混合層, 潮汐 Meteorology, Oceanography, General Circulation, Geostrophic Flow, Midlatitude Weather System, Tropical Meteorology, Numerical Weather Prediction, Atmospheric Boundary Layer, Atmospheric Chemistry, Ozone Layer, Climate Change, Global Warming; Thermohaline Circulation, Wind-driven Circulation, Potential Vorticity, Western Boundary Current, Ocean Mixed Layer, Tide
  • 一般教育演習(フレッシュマンセミナー)
    開講年度 : 2021年
    課程区分 : 学士課程
    開講学部 : 全学教育
    キーワード : 流れの科学、回転水槽実験、大気、海洋、気象、海流、地球流体、天気図

大学運営

委員歴

  • 2021年07月 - 現在   環境省・オゾン層保護に関する検討会・科学分科会・委員
  • 2018年02月 - 現在   WCRP Task Team for Intercomparison of ReAnalyses (TIRA)   Co-chair
  • 2016年10月 - 現在   WCRP Task Team for Intercomparison of ReAnalyses (TIRA)   Member
  • 2016年09月 - 現在   International Ozone Commission (IO3C)   Member
  • 2014年04月 - 現在   気象庁・長期再解析推進委員会/懇談会   委員
  • 2011年06月 - 現在   WCRP SPARC Reanalysis Intercomparison Project (S-RIP)   Co-lead
  • 2010年 - 現在   GRUAN Task Team Radiosonde   Co-chair
  • 2007年12月 - 現在   日本気象学会   「天気」北海道地区編集委員   日本気象学会
  • 2007年03月 - 現在   日本学術会議   環境学委員会・地球惑星科学委員会合同 IGBP・WCRP・DVERSITAS合同分科会SPARC小委員会委員
  • 2006年08月 - 現在   GCOS/AOPC, Working Group on GRUAN (former WG on Atmospheric Reference Observations, renamed in 2012)   Member
  • 2006年07月 - 2022年12月   日本気象学会   Journal of the Meteorological Society of Japan (JMSJ) 編集委員会委員   日本気象学会
  • 2017年 - 2020年07月   Assessment of Operating Procedures for Ozone Sondes (ASOPOS) 2.0   Panel Member
  • 2011年07月 - 2019年   International Commission on the Middle Atmosphere (ICMA)   Member
  • 2016年07月 - 2017年   Scientific Steering Committee of the Ozone Data Quality Assessment (O3S-DQA) and the Jülich Ozone Sonde Intercomparison Experiment (JOSIE)   Member
  • 2004年04月 - 2008年03月   日本気象学会   北海道支部幹事   日本気象学会


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