Komori, Nobumasa



Research Centers and Institutes, Research and Education Center for Natural Sciences (Hiyoshi)


Researcher (Non-tenured) / Project Researcher(Non-tenured)

External Links

Career 【 Display / hide

  • 2002.04

    Japan Marine Science and Technology Center, Earth Simulator Center, Research Scientist

  • 2004.04

    Japan Agency for Marine-Earth Science and Technology, Earth Simulator Center, Scientist

  • 2005

    Tokyo Institute of Technology, Graduate School of Information Science and Engineering, 非常勤講師

  • 2010

    Niigata University, Graduate School of Science and Technology, 非常勤講師

  • 2011.04

    Japan Agency for Marine-Earth Science and Technology, Earth Simulator Center, Senior Scientist

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Academic Background 【 Display / hide

  • 1993.04

    Kyoto University, Faculty of Science, Department of Geophysics

  • 1997.04

    Kyoto University, Graduate School of Science, Division of Earth and Planetary Science

  • 1999.04

    Kyoto University, Graduate School of Science, Division of Earth and Planetary Science


Research Areas 【 Display / hide

  • Natural Science / Atmospheric and hydrospheric sciences

  • Environmental Science/Agriculture Science / Environmental dynamic analysis

Research Keywords 【 Display / hide

  • climatology

  • simulation

  • sea ice

  • physical oceanography

  • ocean general circulation model

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Books 【 Display / hide

  • データ同化―観測・実験とモデルを融合するイノベーション

    淡路 敏之, 池田 元美, 石川 洋一, 蒲地 政文, 京都大学学術出版会, 2009.08,  Page: 284

  • オホーツク海の気象 —大気と海洋の双方向作用—(気象研究ノート 第214号)

    立花, 義裕, 本田, 明治, 日本気象学会, 2007.08,  Page: vi, 178p

    Scope: 第15章 全球大気海洋結合モデルにおけるオホーツク海の海氷

Papers 【 Display / hide

  • EFSO at different geographical locations verified with observing-system experiments

    Akira Yamazaki, Takemasa Miyoshi, Jun Inoue, Takeshi Enomoto, Nobumasa Komori

    Weather and Forecasting (American Meteorological Society)   2021.04

    Accepted,  ISSN  0882-8156

     View Summary

    <title>Abstract</title>An ensemble-based forecast sensitivity to observations (EFSO) diagnosis has been implemented in an atmospheric general circulation model–ensemble Kalman filter data assimilation system to estimate the impacts of specific observations from the quasi-operational global observing system on weekly short-range forecasts. It was examined whether EFSO reasonably approximates the impacts of a subset of observations from specific geographical locations for 6-hour forecasts, and how long the 6-hour observation impacts can be retained during the 7-day forecast period. The reference for these forecasts was obtained from 12 data denial experiments in each of which a subset of three radiosonde observations launched from a geographical location was excluded. The 12 locations were selected from three latitudinal bands comprising (i) four Arctic regions, (ii) four midlatitude regions in the Northern Hemisphere, and (iii) four tropical regions during the Northern Hemisphere winter of 2015/16. The estimated winter-averaged EFSO-derived observation impacts well corresponded to the 6-hour observation impacts obtained by the data denials and EFSO could reasonably estimate the observation impacts by the data denials on short-range (6-hour to 2-day) forecasts. Furthermore, during the medium-range (4-day to 7-day) forecasts, it was found that the Arctic observations tend to seed the broadest impacts and their short-range observation impacts could be projected to beneficial impacts in Arctic and midlatitude North American areas. The midlatitude area located just downstream of dynamical propagation from the Arctic toward the midlatitudes. Results obtained by repeated Arctic data-denial experiments were found to be generally common to those from the non-repeated experiments.

  • A global eddying hindcast ocean simulation with OFES2

    Hideharu Sasaki, Shinichiro Kida, Ryo Furue, Hidenori Aiki, Nobumasa Komori, Yukio Masumoto, Toru Miyama, Masami Nonaka, Yoshikazu Sasai, Bunmei Taguchi

    Geoscientific Model Development (Copernicus GmbH)  13 ( 7 ) 3319 - 3336 2020.07


     View Summary

    Abstract. A quasi-global eddying ocean hindcast simulation using a
    new version of our model, called OFES2 (Ocean General Circulation Model for
    the Earth Simulator version 2), was conducted to overcome several issues with
    unrealistic properties in its previous version, OFES. This paper
    describes the model and the simulated oceanic fields in OFES2 compared with
    OFES and also observed data. OFES2 includes a sea-ice model and a tidal
    mixing scheme, is forced by a newly created surface atmospheric dataset
    called JRA55-do, and simulated the oceanic fields from 1958 to 2016. We found
    several improvements in OFES2 over OFES: smaller biases in the global sea
    surface temperature and sea surface salinity as well as the water mass properties
    in the Indonesian and Arabian seas. The time series of the Niño3.4 and
    Indian Ocean Dipole (IOD) indexes are somewhat better in OFES2 than in OFES.
    Unlike the previous version, OFES2 reproduces more realistic anomalously low
    sea surface temperatures during a positive IOD event. One possible cause of
    these improvements in El Niño and IOD events is the replacement of the
    atmospheric dataset. On the other hand, several issues remained unrealistic,
    such as the pathways of the Kuroshio and Gulf Stream and the unrealistic
    spreading of salty Mediterranean overflow. Given the worldwide use of the
    previous version and the improvements presented here, the output from
    OFES2 will be useful in studying various oceanic phenomena with broad
    spatiotemporal scales.

  • Ensemble-Based Atmospheric Reanalysis Using a Global Coupled Atmosphere-Ocean GCM

    Komori Nobumasa, Enomoto Takeshi, Miyoshi Takemasa, Yamazaki Akira, Kuwano-Yoshida Akira, Taguchi Bunmei

    MONTHLY WEATHER REVIEW (AMER METEOROLOGICAL SOC)  146 ( 10 ) 3311 - 3323 2018.10

    Accepted,  ISSN  0027-0644

     View Summary

    Ensemble-based atmospheric data assimilation (DA) systems are sometimes afflicted with an underestimation of the ensemble spread near the surface caused by the use of identical boundary conditions for all ensemble members and the lack of atmosphere-ocean interaction. To overcome these problems, a new DA system has been developed by replacing an atmospheric GCM with a coupled atmosphere-ocean GCM, in which atmospheric observational data are assimilated every 6 h to update the atmospheric variables, whereas the oceanic variables are subject to no direct DA. Although SST suffers from the common biases among many coupled GCMs, two months of a retrospective analysis-forecast cycle reveals that the ensemble spreads of air temperature and specific humidity in the surface boundary layer are slightly increased and the forecast skill in the midtroposphere is rather improved by using the coupled DA system in comparison with the atmospheric DA system. In addition, surface atmospheric variables over the tropical Pacific have the basinwide horizontal correlation in ensemble space in the coupled DA system but not in the atmospheric DA system. This suggests the potential benefit of using a coupled GCM rather than an atmospheric GCM even for atmospheric reanalysis with an ensemble-based DA system.

  • Using Observations near the Poles in the AFES-LETKF Data Assimilation System

    Akira Yamazaki, Takeshi Enomoto, Takemasa Miyoshi, Akira Kuwano-Yoshida, Nobumasa Komori

    SOLA (METEOROLOGICAL SOC JAPAN)  13   41 - 46 2017

    Accepted,  ISSN  1349-6476

     View Summary

    The observation operators in the local ensemble transform Kalman filter (LETKF) were improved to enable use of observations in the vicinity of the poles in the data assimilation system composed of the atmospheric general circulation model for the Earth Simulator (AFES) and the LETKF. The improved observation operators allow to assimilate the observations located south (north) of southernmost (northernmost) Gaussian grid latitudes. An algorithm for searching the nearest observations from an analyzed grid for error covariance localization was also modified to efficiently assimilate observations near the poles.
    The new algorithms were incorporated into the LETKF, and the impacts of routine radiosonde observations at the South Pole during the periods of July 2012 and January 2013 were assessed. The radiosonde observations suppressed an artificial expansion of the analysis ensemble spread which occasionally caused numerical instability in the upper troposphere and the lower stratosphere over the Antarctic regions. The analysis was also improved in the Antarctic regions.

  • Frontolysis by surface heat flux in the Agulhas Return Current region with a focus on mixed layer processes: observation and a high-resolution CGCM

    Shun Ohishi, Tomoki Tozuka, Nobumasa Komori

    CLIMATE DYNAMICS (SPRINGER)  47 ( 12 ) 3993 - 4007 2016.12

    Accepted,  ISSN  0930-7575

     View Summary

    Detailed mechanisms for frontogenesis/frontolysis of the Agulhas Return Current (ARC) Front, defined as the maximum of the meridional sea surface temperature (SST) gradient at each longitude within the ARC region (40A degrees-50A degrees E, 55A degrees-35A degrees S), are investigated using observational datasets. Due to larger (smaller) latent heat release to the atmosphere on the northern (southern) side of the front, the meridional gradient of surface net heat flux (NHF) is found throughout the year. In austral summer, surface warming is weaker (stronger) on the northern (southern) side, and thus the NHF tends to relax the SST front. The weaker (stronger) surface warming, at the same time, leads to the deeper (shallower) mixed layer on the northern (southern) side. This enhances the frontolysis, because deeper (shallower) mixed layer is less (more) sensitive to surface warming. In austral winter, stronger (weaker) surface cooling on the northern (southern) side contributes to the frontolysis. However, deeper (shallower) mixed layer is induced by stronger (weaker) surface cooling on the northern (southern) side and suppresses the frontolysis, because the deeper (shallower) mixed layer is less (more) sensitive to surface cooling. Therefore, the frontolysis by the NHF becomes stronger (weaker) through the mixed layer processes in austral summer (winter). The cause of the meridional gradient of mixed layer depth is estimated using diagnostic entrainment velocity and the Monin-Obukhov depth. Furthermore, the above mechanisms obtained from the observation are confirmed using outputs from a high-resolution coupled general circulation model. Causes of model biases are also discussed.

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Reviews, Commentaries, etc. 【 Display / hide

  • 第11回データ同化ワークショップの報告

    川畑拓矢, 上野玄太, 中野慎也, 藤井陽介, 三好建正, 小守信正, 増田周平, 伊藤耕介, 村上大輔, 大石俊, 青木邦弘, 青梨和正

    天気 68 ( 9 ) 465 - 468 2021.09

    ISSN  0546-0921

  • 第10回データ同化ワークショップの報告

    川畑拓矢, 上野玄太, 中野慎也, 藤井陽介, 三好建正, 小守信正, 増田周平, 眞木貴史, 土居知将, 野村俊一, 雨宮新, 山崎哲, 露木義

    天気 67 ( 8 ) 455 - 458 2020.08

    ISSN  0546-0921

  • 研究集会「季節予測システムの進展と異常気象の要因分析」の報告

    小林ちあき, 上田学, 竹村和人, 若松俊哉, 小守信正, 時長宏樹, 野口峻佑, 榎本剛

    天気 66 ( 6 ) 451 - 456 2019.06

  • 第9回データ同化ワークショップの報告

    川畑拓矢, 上野玄太, 中野慎也, 藤井陽介, 三好建正, 小守信正, 増田周平, 茂木耕作, 小槻峻司, 澤田洋平, Peter Jan van LEEUWEN 長尾大道

    天気 66 ( 2 ) 161 - 164 2019.02

    ISSN  0546-0921

  • 準全球高解像度海洋過去再現シミュレーションOFES2

    佐々木英治, 古恵亮, 木田新一郎, 木田新一郎, 相木秀則, 相木秀則, 小守信正, 升本順夫, 升本順夫, 美山透, 野中正見, 笹井義一, 田口文明

    日本海洋学会大会講演要旨集 2019 2019

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Research Projects of Competitive Funds, etc. 【 Display / hide

  • Roles of the Kuroshio and Oyashio frontal zones in the air-sea interaction system and predictability of their interannual variability


    Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area), Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area), No Setting

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  • アンサンブルデータ同化を利用した大気海洋結合モードの抽出とその短期予測への応用


    日本学術振興会, 科学研究費助成事業 基盤研究(C), 基盤研究(C), No Setting

     View Summary

    短期変動予測への応用に資するため、全球大気海洋結合モデル CFES へ海面水温の観測データのみを簡便な手法(ナッジ法)を用いて同化する試験的な季節予測システムについて、前年度同様に、毎月1日から6ヶ月間・12メンバーでの予測実験を準リアルタイムで継続した。
    また、大気大循環モデル AFES において、黒海やカスピ海など、全球を対象とした数値モデルでは三次元的に計算することが困難な内海に関して、非一様な水深分布を入力可能なように改良し、より現実的な水温変動が再現できることを確認した。さらに、内海に高温偏差が存在する場合、内海と周辺の陸域との熱的コントラストに起因して、風上側で発散偏差・風下側で収束偏差が生じ、海岸線に沿った発散域で少雨偏差・収束域で多雨偏差が生じ得ること、これらに伴い、内海周辺での降水分布も改善することを見出した。
    AFES と局所アンサンブル変換カルマンフィルタ (LETKF) を用いたアンサンブルデータ同化システム ALEDAS2 に、一つ一つの観測データに対する予報感度を診断できる EFSO と呼ばれる手法を導入し、実験結果をまとめた共著論文が、アメリカ気象学会が出版する Weather and Forecasting 誌に受理・オンライン公開された。この論文では、北極域・中緯度域・熱帯域のいずれの緯度帯においても2-3日先までの予報に対する影響を正しく推定できること、特に北極域の観測データは北米の6-7日先の予報を改善しうることを示した。

  • Ekman-pumping forced model: Basic concept and implementation for causality understanding of tropical ocean variability


    Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Challenging Exploratory Research, Minobe Shoshiro, Grant-in-Aid for Challenging Exploratory Research, No Setting

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    Ekman pumping is a fundamental tool for understanding the causality in ocean variability except for the equator, where Ekman pumping becomes infinity. We have solved this difficulty by proposing and producing Ekman-pumping forced model for the first time and its adjuring backward integration version. By conducting a series of numerical experiments, we have found that off-equatorial Ekman pumping contribute more strongly in the Indian Ocean rather than in the Pacific Ocean for the equatorial upper layer thickness variability. Also, off-equatorial Ekman pumping contributes more for large-magnitude events of Indian Ocean dipole mode than for small magnitude events.

  • 大気海洋結合データ同化システムを用いた大気と海洋表層の共変動過程の解明


    文部科学省, 科学研究費補助金(基盤研究(C)), 基盤研究(C), Principal investigator

  • 人工衛星観測データを用いた実験的海氷変動予測システムの開発


    文部科学省, 科学研究費補助金(若手研究(B), 若手研究(B)), 若手研究(B), 若手研究(B), Principal investigator

     View Summary

    データ同化の成否は、観測データの質・量のみならず、使用する数値モデルの性能にも大きく左右されるため、平成23年度も引き続き、海洋海氷結合モデルOFES(Ocean General Circulation Model for the Earth Simulator)の改良を行った。特に、OFESの基となった海洋大循環モデルMOM3(Modular Ocean Model version3)における短波透過の取扱いの問題点とその影響を定量的に評価した。一方、実験的海氷変動予測システムESPreSSOの開発に当たり、当初は海洋海氷結合モデルOFESを使用する予定であったが、検討した結果、海氷および海洋表層におけるアンサンブルメンバー間のばらつき(スプレッド)を十分大きくするためには、大気海洋海氷結合モデルCFES(Coupled Atmoephere-Ocean Model for the Earth Simulator)を使用する方がより適切であることが判明した。そこで計画をやや変更し、CFESを用いた大気海洋海氷結合アンサンブルデータ同化システムのプロトタイプを構築した。現状では大気の観測データのみを同化可能であるが、数ヶ月間の解析・予報サイクルが安定して動作していることを確認した。平成24年度には、海面水温と海氷密接度・海氷厚の観測データを同化する機能を実装する予定である。ま...

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Courses Previously Taught 【 Display / hide

  • 自然環境科学



  • 環境数値シミュレーション2




Academic Activities 【 Display / hide

  • データ同化研究連絡会


Memberships in Academic Societies 【 Display / hide

  • Japan Geoscience Union, 

  • Meteorological Society of Japan, 

  • Oceanographic Society of Japan, 


Committee Experiences 【 Display / hide

  • 2014.05

    2014年度春季大会実行委員, 日本気象学会

  • 2011.11

    JOSニュースレター編集委員, 日本海洋学会

  • 2008.05

    2008年度春季大会実行委員, 日本気象学会