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FUJIWARA Yasushi
Graduate School of Maritime Sciences / Department of Maritime Sciences
Assistant Professor

Research activity information

■ Award
  • Sep. 2019 日本海洋学会, 2019年秋季大会 若手優秀発表賞, 水面波との双方向相互作用によるLangmuir循環の自己強化機構
    藤原泰

  • Oct. 2017 日本海洋学会, 2017年秋季大会 若手優秀発表賞, 直接数値計算されたLangmuir循環の駆動機構 – Euler的視点での解釈
    藤原泰

  • Sep. 2016 日本海洋学会, 2016年秋季大会 若手優秀発表賞, 深水波の直接数値計算: CL2機構によるLangmuir循環
    藤原泰

■ Paper
  • Yasushi Fujiwara, Takuji Waseda, Tsubasa Kodaira, Takehiko Nose, Tomotaka Katsuno, Koya Sato
    Elsevier BV, May 2025, Cold Regions Science and Technology, 233, 104449
    [Refereed]
    Scientific journal

  • Haruka Imamura, Yutaka Yoshikawa, Yasushi Fujiwara
    Abstract Direct numerical simulations of the turbulence induced by nonbreaking surface waves were conducted to clarify the turbulence generation mechanism and evaluate the turbulent mixing intensity with a sigma-coordinate free-surface nonhydrostatic model. One of the simulations was modeled after a previously reported laboratory experiment with a wave of 30 cm wavelength and 1 cm amplitude freely propagating on the initially stratified water under a windless condition. The simulation showed that organized vortex pairs like Langmuir circulations (LCs) grew, and the water was mixed vertically. The enstrophy budget analysis revealed that the vortex pairs were generated nonlocally through the interaction between surface waves and a surface shear flow, the same mechanism for the LCs, except that the flow is forced by not the wind but the virtual wave stress due to viscous wave attenuation. The analysis also revealed that the local turbulence generation mechanism by the wave orbital motions (as inferred by the previous laboratory study) did not work in our simulated turbulence. The simulated eddy diffusivity was $$\varvec{O}$$ (10 $$^{\varvec{-5 } }$$  m $$^{\varvec{2 } }$$  s $$^{\varvec{-1 } }$$ ) and its vertical profile and temporal changes were different from those of the parameterized diffusivity based on the local turbulence generation mechanism. The nonbreaking wave-induced mixing observed in our simulations under windless conditions is expected to occur in the real open ocean. These results suggest that to parameterize this mixing, parameterization of the nonlocal Langmuir turbulence, with wind stress replaced by virtual wave stress, could be an effective approach.
    Springer Science and Business Media LLC, Mar. 2025, Ocean Dynamics, 75(3) (3)
    [Refereed]
    Scientific journal

  • Yasushi Fujiwara
    Even without breaking or wind influence, ocean surface waves are observed to produce turbulence in the water, possibly influencing ocean surface dynamics and air–sea interactions. Based on the water-side free-surface simulations, recent studies suggest that such turbulence is produced through the interaction between the waves and the near-surface Eulerian current associated with the viscous attenuation of waves. To clarify the dynamical role of the air–water interface in the turbulence production, the attenuating interfacial gravity waves were simulated directly using a newly developed two-phase wave-resolving numerical model. The air–water coupling enhanced the wave energy dissipation through the formation of a strong shear at the air-side viscous boundary layer. This led to an enhancement of the wave-to-current momentum transfer and the formation of the down-wave Eulerian mean sheared current, which is favourable for the CL2 instability responsible for the production of Langmuir circulations. As a result, the water-side turbulence grew stronger compared with the corresponding free surface (water-only) wave-resolving simulation. The evolution of the wave-averaged field was well reproduced with the Craik–Leibovich equation with the upper boundary condition provided with the virtual wave stress based on linear theory. The wave energy dissipation by air–water coupling plays a significant role in the quantitative understanding of the wave-induced turbulence at the laboratory and field scales.
    Cambridge University Press (CUP), Nov. 2024, Journal of Fluid Mechanics, 999, A97, English
    [Refereed]
    Scientific journal
    Link to Kobe Univ. Repository (Kernel)

  • Takehiko Nose, Jean Rabault, Takuji Waseda, Tsubasa Kodaira, Yasushi Fujiwara, Tomotaka Katsuno, Naoya Kanna, Kazutaka Tateyama, Joey Voermans, Tatiana Alekseeva
    Norwegian Polar Institute, Aug. 2023, Polar Research, 42
    [Refereed]
    Scientific journal

  • Takuji Waseda, Alberto Alberello, Takehiko Nose, Takenobu Toyota, Tsubasa Kodaira, Yasushi Fujiwara
    Waves in the Marginal Ice Zone in the Okhotsk Sea are less studied compared to the Antarctic and Arctic. In February 2020, wave observations were conducted for the first time in the Okhotsk Sea, during the observational program by Patrol Vessel Soya. A wave buoy was deployed on the ice, and in situ wave observations were made by a ship-borne stereo imaging system and Inertial Measurement Unit. Sea ice was observed visually and by aerial photographs by drone, while satellite synthetic aperture radar provided basin-wide spatial distribution. On 12 February, a swell system propagating from east northeast was detected by both the stereo imaging system and the buoy-on-ice. The wave system attenuated from 0.34 m significant wave height to 0.25 m in about 90 km, while the wave period increased from 10 s to 15–17 s. This anomalous spectral downshifting was not reproduced by numerical hindcast and by applying conventional frequency-dependent exponential attenuation to the incoming frequency spectrum. The estimated rate of spectral downshifting, defined as a ratio of momentum and energy losses, was close to that of uni-directional wave evolution accompanied by breaking dissipation: this indicates that dissipation-driven nonlinear downshifting may be at work for waves propagating in ice. This article is part of the theme issue 'Theory, modelling and observations of marginal ice zone dynamics: multidisciplinary perspectives and outlooks'.
    The Royal Society, Oct. 2022, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 380(2235) (2235), English
    [Refereed]
    Scientific journal

  • Yasushi Fujiwara, Yutaka Yoshikawa, Yoshimasa Matsumura
    Elsevier BV, Oct. 2020, Ocean Modelling, 154, 101679 - 101679
    [Refereed]
    Scientific journal

  • Yasushi Fujiwara, Yutaka Yoshikawa
    Abstract Wave-resolving simulations of monochromatic surface waves and Langmuir circulations (LCs) under an idealized condition are performed to investigate the dynamics of wave–current mutual interaction. When the Froude number (the ratio of the friction velocity of wind stress imposed at the surface and wave phase speed) is large, waves become refracted by the downwind jet associated with LCs and become amplitude modulated in the crosswind direction. In such cases, the simulations using the Craik–Leibovich (CL) equation with a prescribed horizontally uniform Stokes drift profile are found to underestimate the intensity of LCs. Vorticity budget analysis reveals that horizontal shear of Stokes drift induced by the wave modulation tilts the wind-driven vorticity to the downwind direction, intensifying the LCs that caused the waves to be modulated. Such an effect is not reproduced in the CL equation unless the Stokes drift of the waves modulated by LCs is prescribed. This intensification mechanism is similar to the CL1 mechanism in that the horizontal shear of the Stokes drift plays a key role, but it is more likely to occur because the shear in this interaction is automatically generated by the LCs whereas the shear in the CL1 mechanism is retained only when a particular phase relation between two crossing waves is kept locked for many periods.
    American Meteorological Society, Aug. 2020, Journal of Physical Oceanography, 50(8) (8), 2323 - 2339
    [Refereed]
    Scientific journal

  • Yasushi Fujiwara, Yutaka Yoshikawa, Yoshimasa Matsumura
    Abstract Fujiwara et al. explicitly simulated Langmuir circulations using a wave-resolving simulation (WRS) technique and found that the residual wave effect on vorticity was well represented by the vortex force of the Craik–Leibovich (CL) equation, at least in the simulated situation. In response to the simulation results, Mellor has proposed a view that ubiquitous applicability of the CL formulation is still questionable and that the three-dimensional radiation stress (3DRS) formulation that he has derived encompasses both of the vortex force effect and an effect that is lower order in terms of wave steepness. Here, these opinions are discussed in terms of the approximations used in the wave-averaged formulations. The asymptotic expansion of the Eulerian-averaged momentum equation allows the separate discussion of two different wave effects: pressure correction and torque. It is argued that the approximation adopted in Mellor’s 3DRS formulation is presumably not accurate enough to properly parameterize the wave torque effect, and possible approaches to examine its performance are proposed. We agree with the view that the applicability of the CL formulation needs further investigation. WRS will be a helpful tool for this purpose.
    American Meteorological Society, Mar. 2019, Journal of Physical Oceanography, 49(3) (3), 889 - 892
    Scientific journal

  • Yasushi Fujiwara, Yutaka Yoshikawa, Yoshimasa Matsumura
    Abstract The present study performs a wave-resolving simulation of wind-driven currents under monochromatic surface gravity waves using the latest nonhydrostatic free-surface numerical model. Here, phase speed of the waves is set much greater than the current speed. Roll structures very similar to observed Langmuir circulations (LCs) appear in the simulation only when both waves and down-wave surface currents are present, demonstrating that the rolls are driven by the wave–current interaction. A vorticity analysis of simulated mean flow reveals that the rolls are driven by the torque associated with wave motion, which arises from a correlation between wave-induced vorticity fluctuation and the wave motion itself. Furthermore, it is confirmed that the wave-induced torque is very well represented by the curl of the vortex force (VF), that is, the vector product of mean vorticity and Stokes drift velocity. Therefore, it is concluded that the simulated rolls are LCs and that the wave effects are well represented by the VF expression in the present simulation. The present study further revisits the scaling assumptions made by previous studies that derived VF formulation and shows that there is disagreement among the previous studies regarding the applicability of VF formulation when the wave orbital velocity (proportional to the amplitude times the frequency) is much smaller than the mean flow velocity. The result from the present simulation shows that the VF expression is still valid even with such small wave amplitudes, as long as phase speed of the waves is much greater than the current speed.
    Aug. 2018, Journal of Physical Oceanography, 48(8) (8), 1691 - 1708, English
    [Refereed]
    Scientific journal

■ MISC
  • 第6回非静力学モデルに関する国際ワークショップ（第25回非静力学モデルに関するワークショップ）の報告
    佐藤陽祐, 稲津將, 南出将志, 柳瀬友朗, 近藤誠, 大塚成徳, 吉田龍二, 佐藤拓人, 宮本佳明, 藤原泰, 末木健太, 高須賀大輔, 伊藤純至, 橋本明弘, 八代尚
    Feb. 2024, 天気, 75(2) (2), Japanese
    Meeting report

■ Lectures, oral presentations, etc.
  • 海洋表層LESを用いたマイクロプラスチック水平輸送のラングミュア数依存性
    福本剛史, 藤原泰
    日本地球惑星科学連合2025年大会, May 2025, Japanese
    Oral presentation

  • Numerical study of turbulence production by nonbreaking surface waves
    藤原泰
    日本地球惑星科学連合2025年大会, May 2025, Japanese
    [Invited]
    Invited oral presentation

  • 海洋物理分野における波と流れの相互作用
    藤原泰
    名古屋大学宇宙地球環境研究所共同利用研究集会「海洋波および大気海洋相互作用に関するワークショップ」, Mar. 2025
    [Invited]

  • オホーツク海で発達した爆弾低気圧でのうねりと風波
    野瀬 毅彦, 早稲田 卓爾, 小平 翼, 藤原 泰, 豊田 威信
    第39回北方圏国際シンポジウム「オホーツク海と流氷」, Feb. 2025
    Oral presentation

  • Nonlinear growth of swell by wind under cross sea
    T. Nose, T. Waseda, K. Nishizawa, T. Kodaira, Y. Fujiwara, A. Alberello
    The 6th Workshop on Waves and Wave-Coupled Processes, Jan. 2025

  • Direct numerical simulation of air-sea momentum exchange through irregular waves
    Yasushi Fujiwara
    第38回数値流体力学シンポジウム, Dec. 2024, Japanese
    Oral presentation

  • むつ小川原試験サイトにおける小型係留式海象観測ブ イSpotterの波浪･風況の精度検証
    佐野 朝昭, 門 安曇, 麻生 裕司, 中尾 徹, 永山 龍之介, 田中 仁, 大澤 輝夫, 藤原 泰
    第46回 風力エネルギー利用シンポジウム, Nov. 2024, Japanese
    Oral presentation

  • 風波の発達と運動量フラックスについて - 直接数値計算の初期解析結果 -
    藤原泰
    愛媛大学LaMer 2024年度共同利用研究集会 「海洋乱流の観測およびモデリングに関する研究集会」, Nov. 2024, Japanese
    Oral presentation

  • 風波の発達と運動量フラックス
    藤原泰
    海洋の統合的理解に向けた新時代の力学理論の構築, Oct. 2024, Japanese
    Oral presentation

  • Numerical study of the wave-induced mass transport and consequent counter-current response in the coastal ocean
    Yasushi Fujiwara, Yoshimasa Matsumura
    the 14th International Workshop on Modeling the Ocean, Jun. 2024, English
    Oral presentation

  • 北極海カナダ海盆の海氷縁付近におけるメゾスケール渦とサブメゾスケール渦
    小平 翼, 早稲田 卓爾, 藤原 泰, 君塚 政文, 勝野 智嵩, 川口 悠介, 野瀬 毅彦, 藤原 周
    日本地球惑星科学連合2024年大会, May 2024, Japanese
    Poster presentation

  • LESを用いた浮遊物水平輸送の混合層深度による影響評価
    福本剛史, 藤原泰
    日本地球惑星科学連合2024年大会, May 2024, Japanese
    Poster presentation

  • Mass transport and consequent counter-transport induced by waves (2) - response in a rotating system
    藤原泰, 松村義正
    日本地球惑星科学連合2024年大会, May 2024, Japanese
    Poster presentation

  • Short-term wave and ice forecast for navigation assistance in the Arctic Ocean
    Takuji Waseda, Yasushi Fujiwara, Xingkun Xu, Tak Nose, Tsubasa Kodaira
    The 5th workshop on waves and wave-coupled processes, Apr. 2024

  • 減衰するうねりに伴う気液間運動量・エネルギー輸送の解析
    藤原泰
    名古屋大学宇宙地球環境研究所共同利用研究集会「海洋波および大気海洋相互作用に関するワークショップ」, Mar. 2024
    Oral presentation

  • Research on spectral downshifting of waves propagating under sea ice
    佐藤公哉, 早稲田卓爾, 小平翼, 藤原泰, 野瀬毅彦, 勝野智嵩
    第38回 北方圏国際シンポジウム, Feb. 2024

  • Direct observation of submesoscale and mesoscale eddies by ocean surface drifters near the sea ice edge in the Canada Basin, Arctic Ocean
    小平翼, 早稲田卓爾, 勝野智嵩, 君塚政文, 藤原泰, 野瀬毅彦, 川口悠介, 藤原周
    第38回 北方圏国際シンポジウム, Feb. 2024

  • 波浪による海水輸送と波と流れの相互作用
    藤原泰, 松村義正
    北海道大学低温科学研究所共同利用研究集会「海洋乱流の観測およびモデリングに関する研究集会」, Dec. 2023
    Oral presentation

  • 波浪による海水輸送と反流
    藤原泰, 松村義正
    北海道大学低温科学研究所共同利用研究集会「海洋の統合的理解に向けた新時代の力学理論の構築」, Nov. 2023
    Oral presentation

  • 地球自転影響下でのストークス輸送と反流応答の数値計算
    藤原泰, 松村義正
    微細規模から惑星規模にかけての海洋力学過程と規模間相互作用の研究, Oct. 2023
    Oral presentation

  • 波浪に伴う海水輸送と反流応答 (1)：直接数値計算による検証
    藤原泰, 松村義正
    日本海洋学会2023年秋季大会, Sep. 2023, Japanese
    Oral presentation

  • ストークス輸送と海洋モデリング
    藤原泰
    マクロ沿岸海洋学2023年度サマースクール, Sep. 2023, Japanese
    Public discourse

  • A numerical model for the direct simulation of wind-wave interaction
    Yasushi Fujiwara
    The 6th International Workshop on Nonhydrostatic Numerical Models, Sep. 2023, English
    Oral presentation

  • A non-hydrostatic ocean model for multi-scale/multi-process simulations
    Yoshimasa Matsumura, Yasuhiro Hoshiba, Yasushi Fujiwara, Shinichiro Kida, Takateru Yamagishi
    The 6th International Workshop on Nonhydrostatic Numerical Models, Aug. 2023, English
    Oral presentation

  • ミクロスケール大気海洋相互作用の研究のための波解像二相数値モデルの開発
    藤原泰
    日本地球惑星科学連合2023年大会, May 2023, Japanese
    Poster presentation

  • A direct numerical simulation of nonbreaking-surface-waves induced mixing
    Yutaka Yoshikawa, Haruka Imamura, Yasushi Fujiwara
    EGU General Assembly 2023, English
    Oral presentation

  • Impacts of non-breaking wave induced mixing on the modelling of Arctic Cyclone through the two-way coupled numerical model
    Xingkun Xu, Yasushi Fujiwara, Takehiko Nose, Tsubasa Kodaira, Takuji Waseda
    Seventh International Symposium on Arctic Research, English
    Poster presentation

  • Experimental research on spectral downshift of propagating waves under sea ice
    Koya Sato, Takuji Waseda, Tsubasa Kodaira, Yasushi Fujiwara, Takehiko Nose, Tomotaka Katsuno
    Seventh International Symposium on Arctic Research, English
    Poster presentation

  • Laboratory experiment of ice group formation under waves
    Yasushi Fujiwara, Takuji Waseda, Tsubasa Kodaira, Takehiko Nose, Tomotaka Katsuno, Koya Sato
    Seventh International Symposium on Arctic Research, English
    Poster presentation

  • 界面追従座標に基づく気液結合境界層数値モデルの開発
    藤原泰
    海洋波および大気海洋相互作用に関するワークショップ, Mar. 2023, Japanese
    Oral presentation

  • Waves, ice, and current measurements using 5-beam ADCP at the Barrow Canyon - one year of mooring observation from September 2021
    Tsubasa Kodaira, Yasushi Fujiwara, Motoyo Itoh, Takehiko Nose, Tomotaka Katsuno, Takuji Waseda
    the 37th International Symposium on Okhotsk Sea and Polar Oceans
    Oral presentation

  • 波浪境界層の直接計算のための気液非静力学モデルの開発
    藤原 泰
    北海道大学低温科学研究所共同研究「海洋の統合的理解に向けた新時代の力学理論の構築」, Nov. 2022
    Oral presentation

  • 大気海洋結合境界層数値モデルの開発
    藤原 泰
    九州大学応用力学研究所共同利用研究 「微細規模から惑星規模にかけての海洋力学過程と規模間相互作用の研究」研究集会, Nov. 2022
    Oral presentation

  • Development of MEMS-IMU based and solar powered wave buoy FZ
    Tsubasa Kodaira, Tomotaka Katsuno, Yasushi Fujiwara, Takehiko Nose, Jean Rabault, Joey Voermans, Masafumi Kimizuka, Takuji Waseda
    OCEANS Conference 2022 Hampton Roads, Oct. 2022
    Oral presentation

  • 融解期の北極海で観測された海氷漂流の密接度依存性
    藤原泰, 小平翼, 早稲田卓爾, 野瀬毅彦
    日本海洋学会 2022年秋季大会, Sep. 2022
    Oral presentation

  • MEMS-IMUを用いた漂流型波浪ブイ開発の試み
    小平翼, 勝野智嵩, 藤原泰, 野瀬毅彦, Jean Rabault, Joey Voermans, 君塚政文, 早稲田卓爾, 豊田威信
    日本海洋学会 2022年秋季大会, Sep. 2022
    Oral presentation

  • 海氷運動の時間スケールと要因の解析
    藤原泰, 小平翼, 早稲田卓爾, 野瀬毅彦
    海洋表層関連過程に関する分野間交流ワークショップ, Jul. 2022
    Oral presentation

  • Direct numerical simulation of nonbreaking surface-wave-induced mixing: intensity and mechanism of the mixing
    Haruka Imamura, Yutaka Yoshikawa, Yasushi Fujiwara
    The 12th International Workshop on Modeling the Ocean, Jun. 2022
    Oral presentation

  • Verification of the use of Google Cloud Platform for calculating a real-time forecast model
    照井 健志, 藤原 泰, 野瀬 毅彦, 大山 元夢
    日本地球惑星科学連合2022年大会, May 2022
    Poster presentation

  • 海氷漂流の風への応答 - 太平洋側北極海での観測
    藤原 泰, 小平 翼, 早稲田 卓爾, 野瀬 毅彦, 西澤 啓太, 内山 亮介
    日本地球惑星科学連合2022年大会, May 2022
    Oral presentation

  • Direct numerical simulation of vertical mixing due to the nonbreaking surface wave: Eddy diffusivity estimation and enstrophy analysis
    Haruka Imamura, Yutaka Yoshikawa, Yasushi Fujiwara
    Ocean Sciences Meeting 2022, Feb. 2022

  • Interannual variation of sea ice concentration over the Canada Basin
    Kodaira T, Waseda T, Nose T, Fujiwara Y
    the 36th International Symposium on Okhotsk Sea and Polar Oceans, Feb. 2022
    Oral presentation

  • Analysis on long-term trend of vessel icing predictor in the Arctic Ocean and measurement of sea spray and waves on R/V Mirai
    Uchiyama R, Waseda T, Nose T, Kodaira T, Fujiwara Y, Yamaguchi H
    the 36th International Symposium on Okhotsk Sea and Polar Oceans, Feb. 2022
    Oral presentation

  • Radar observation of sea-ice and waves in a controlled laboratory environment
    Waseda T, Matsuzawa T, Tateyama T, Kodaira T, Fujiwara Y, Katsuno T, Nose T, Nishizawa K, Sato K, Uchiyama R
    the 36th International Symposium on Okhotsk Sea and Polar Oceans, Feb. 2022
    Oral presentation

  • Lagrangian observation of sea ice drift
    Fujiwara, Y, Kodaira, K, Waseda, T, Nose, T, Nishizawa, K, Uchiyama, R
    the 36th International Symposium on Okhotsk Sea and Polar Oceans, Feb. 2022
    Oral presentation

  • 海氷漂流のラグランジュ的観測
    藤原泰, 小平翼, 早稲田卓爾, 野瀬毅彦, 西澤啓太, 内山亮介
    北極域研究に関する分野横断研究の発展のためのボトムアップ型研究集会, Dec. 2021
    Oral presentation

  • 北極海における波浪海氷相互作用の観測的・実験的研究
    藤原泰
    北極環境研究コンソーシアム2021年度全体集会および講演会, Nov. 2021, Japanese
    [Invited]

  • MEMSセンサを用いた波浪計測機器開発の試み
    小平翼, 麻崎和大, 勝野智嵩, 野瀬毅彦, 藤原泰, 内山亮介, Jean Rabault, Joey Voermans, 早稲田卓爾
    日本船舶海洋工学会 令和3年秋季講演会, Nov. 2021
    Oral presentation

  • 波浪存在下における氷盤形成の水槽実験
    藤原泰, 勝野智嵩, 早稲田卓爾, 野瀬毅彦, 小平翼
    日本地球惑星科学連合2021年大会, Jun. 2021
    Oral presentation

  • 砕波しない波単独による混合についての波解像数値実験
    今村春香, 吉川裕, 藤原泰
    日本地球惑星科学連合2021年大会, Jun. 2021
    Oral presentation

  • Analysing trend of MIZ fraction and largest waves in the Arctic Ocean and the Antarctic
    Takehiko Nose, Takuji Waseda, Tsubasa Kodaira, Yasushi Fujiwara
    Joint Seminar on Mombetsu Sea Ice Symposium, Mar. 2021

  • 氷海造波水槽における波浪・海氷相互作用の実験
    藤原泰, 勝野智嵩, 早稲田卓爾, 野瀬毅彦, 小平翼
    海洋波および大気海洋相互作用に関するワークショップ, Mar. 2021
    Oral presentation

  • Verification of the use of Google Cloud Platform by calculating a real-time forecast model
    Takeshi Terui, Yasushi Fujiwara, Takehiko Nose
    The 11th Symposium on Polar Sciences, Dec. 2020
    Poster presentation

  • 波と Langmuir 循環の結合過程のパラメタ依存性
    藤原泰, 吉川裕
    海洋乱流に関する観測およびモデリング研究集会, Oct. 2020
    Oral presentation

  • Directly Simulated Wave-Current Mutual Interaction: Surface Wave Modulation Intensifies Langmuir Circulations
    Fujiwara, Y, Yoshikawa, Y
    Ocean Sciences Meeting 2020, Feb. 2020
    Oral presentation

  • On the Physical Mechanisms of the Two-Way Coupling between a Surface Wave Field and a Circulation Consisting of a Roll and Streak
    Suzuki, N, Fujiwara, Y
    Ocean Sciences Meeting 2020, Feb. 2020
    Oral presentation

  • 水面波との双方向相互作用によるLangmuir循環の自己強化機構
    藤原泰, 吉川裕
    日本海洋学会2019年度秋季大会, Sep. 2019
    Oral presentation

  • 直接数値計算された波とLangmuir循環の双方向相互作用
    藤原泰, 吉川裕
    第4回新海洋混合学 OMIX YMR サマースクール, Aug. 2019
    Oral presentation

  • Wave-resolving simulation as a tool of wave-induced mixing studies
    Fujiwara, Y, Yoshikawa, Y, Matsumura, Y
    26th meeting on Waves In the Shallow Water, May 2019
    Poster presentation

  • 水面波と乱流の直接数値計算 – 平均流理論との比較に向けて
    藤原泰, 吉川裕, 松村義正
    海洋波および大気海洋相互作用に関するワークショップ, Mar. 2019
    Oral presentation

  • 水面波とLangmuir循環の研究 — 平均流理論から直接数値計算へ —
    藤原泰, 吉川裕, 松村義正
    大気海洋相互作用に関する研究集会, Dec. 2018
    Poster presentation

  • Virtual wave stressの直接数値計算
    藤原泰, 吉川裕, 松村義正
    微細規模から惑星規模にかけての海洋力学過程と規模間相互作用の研究, Nov. 2018
    Oral presentation

  • Wave resolving simulation of Langmuir circulations and an Eulerian view of their driving mechanism
    Fujiwara, Y, Yoshikawa, Y, Matsumura, Y
    ACCME 3rd Workshop on Ocean Surface Waves and Wave-coupled Processes, Oct. 2018
    Oral presentation

  • Explicit simulation of deep-water waves and Langmuir circulations
    Fujiwara, Y, Yoshikawa, Y, Matsumura, Y
    NHOM-Brest: Workshop on Non-Hydrostatic Ocean Modeling, Oct. 2018
    Oral presentation

  • 曲線座標自由表面数値モデルの開発と、それを用いた水面波と流れの相互作用の研究
    藤原泰, 吉川裕, 松村義正
    第3回新海洋混合学 OMIX YMR サマースクール, Oct. 2018
    Poster presentation

  • 水面波に伴う粘性応力の数値計算
    藤原泰, 吉川裕, 松村義正
    日本海洋学会2018年度秋季大会, Sep. 2018
    Oral presentation

  • A wave resolving numerical simulation of Langmuir circulations: dynamical analysis of driving mechanism and comparison with Craik-Leibovich theory
    Fujiwara, Y, Yoshikawa, Y, Matsumura, Y
    Frontiers in Oceanic, Atmospheric, and Cryospheric Boundary Layers, May 2018
    Poster presentation

  • 波浪・乱流相互作用の研究のための鉛直可変格子自由表面モデルの開発
    藤原泰, 吉川裕, 松村義正
    海洋乱流の観測およびモデリングに関する研究集会, Mar. 2018
    Oral presentation

  • 水面波と海洋表層乱流の双方向相互作用のシミュレーションに向けて
    藤原泰, 吉川裕, 松村義正
    海洋波および大気海洋相互作用に関するワークショップ, Mar. 2018
    Oral presentation

  • A Direct Numerical Simulation of Langmuir Circulations with Nonhydrostatic Free-surface Model: Dynamical Analysis of Driving Mechanism and Comparison with Vortex Force Formulation
    Fujiwara, Y, Yoshikawa, Y, Matsumura, Y
    Ocean Sciences Meeting 2018, Feb. 2018
    Poster presentation

  • ラングミュア循環の観測と数値シミュレーション
    吉川裕, 藤原泰
    2017年度日本海洋学会西南支部・水産海洋学会合同シンポジウム, Dec. 2017

  • 水面波と風成流の双方向相互作用のシミュレーション
    藤原泰, 吉川裕, 松村義正
    海洋大循環の力学 -- エクマン層から中深層循環まで, Oct. 2017
    Oral presentation

  • 直接数値計算されたLangmuir循環の駆動機構 – Euler的視点での解釈
    藤原泰, 吉川裕, 松村義正
    日本海洋学会2017年度秋季大会, Oct. 2017
    Oral presentation

  • 直接数値計算によるLangmuir乱流の研究
    藤原泰
    学際大規模情報基盤共同利用・共同研究拠点第9回シンポジウム, Jul. 2017
    Poster presentation

  • 水面波の直接数値計算によるLangmuir循環の力学に関する研究
    藤原泰, 吉川裕, 松村義正
    海洋波および大気海洋相互作用に関するワークショップ, Mar. 2017
    Oral presentation

  • 深水波の直接数値計算: CL2機構によるLangmuir循環
    藤原泰, 吉川裕, 松村義正
    日本海洋学会2016年度秋季大会, Sep. 2016
    Oral presentation

  • 回転系における深水波の直接数値シミュレーション
    藤原泰, 吉川裕, 松村義正
    日本地球惑星科学連合2016年度大会, May 2016
    Oral presentation

  • 深水波の直接数値計算: 深水波が表層流に及ぼす影響
    藤原泰, 吉川裕, 松村義正
    日本海洋学会2016年春季大会, Mar. 2016

  • エクマン・ストークス流のシミュレーション
    藤原泰, 吉川裕, 松村義正
    海洋乱流の観測およびモデリングに関する研究集会, Jan. 2016

  • エクマン・ストークス流のシミュレーション
    藤原泰, 吉川裕, 松村義正
    日本海及び日本周辺海域の海況モニタリングと波浪計測に関する研究集会, Dec. 2015

■ Research Themes
  • 日本近海における波浪・海流相互作用の描像と次世代モデリングの探求
    藤原 泰
    日本学術振興会, 科学研究費助成事業, 学術変革領域研究(A), 神戸大学, 01 Apr. 2025 - 31 Mar. 2027

  • 風と波の非平衡状態における大気海洋相互作用の数値的研究
    藤原 泰
    日本学術振興会, 科学研究費助成事業, 若手研究, 神戸大学, 01 Apr. 2024 - 31 Mar. 2027

  • 波浪による海水輸送と反流応答の力学の解明
    藤原 泰
    日本学術振興会, 科学研究費助成事業 学術変革領域研究(A) 公募研究, 学術変革領域研究(A) 公募研究, 神戸大学, Apr. 2023 - Mar. 2025, Principal investigator

  • 波浪を介した大気海洋間運動量輸送の数値的研究
    藤原 泰
    日本学術振興会, 科学研究費助成事業 研究活動スタート支援, 研究活動スタート支援, 神戸大学, 31 Aug. 2022 - 31 Mar. 2024

  • A study on wave-mean flow interaction in the oceanic surface boundary layer through direct numerical simulations of surface waves
    藤原 泰
    Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for JSPS Fellows, Grant-in-Aid for JSPS Fellows, Kyoto University, 26 Apr. 2017 - 31 Mar. 2020
    前年度までに開発した自由表面数値モデルと解析手法を用いて、相互作用する波とLangmuir循環の直接数値計算を多様な強制力パラメタのもとで行った。具体的にはFroude数（風応力に対応する摩擦速度と波の位相速度の比）および波形勾配（振幅と波数の積）を様々に変化させて、同一の初期条件からスタートして単色波の直接計算と対応する波平均計算の比較を行った。 その結果、特にFroude数が大きい状況において、直接数値計算で生じるLangmuir循環は従来の波平均計算によるものよりも強くなることが明らかになった。これは、海洋表層乱流の数値的研究において広く用いられているCraik-Leibovich方程式の枠組みではLangmuir循環の強度が過小評価されてしまうことを示唆する結果である。さらに、そのような状況では波が流れの影響を受けて峰方向（伝播方向に直交する方向）に振幅変調することが観測できた。 循環強度差の原因を調べるため、前年度に開発した曲線座標上の診断手法を用いて渦度収支を解析した。その結果、直接計算と波平均計算との差は波の空間変調によって生じるStokesドリフトの水平変化によって生じていることがわかった。この機構では流れから波への影響が中心的な役割を果たしており、それゆえこの結果は波平均理論単独では表現されないものである。 以上の結果はLangmuir循環を記述する従来の理論に取り入れられていなかった過程の重要性を示す画期的なものであり、新たな枠組みでの波・流れ相互作用過程のモデル化を動機づけるものである。

  • Turbulent mixing of momentum due to Langmuir circulation: Field and numerical experiments
    Yoshikawa Yutaka, Baba Yasuyuki, Mizutani Hideaki, Yufu Kei, Ushijima Yusuke, Fujiwara Yasushi, Mannen Takahiro
    Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (B), Kyoto University, 01 Apr. 2013 - 31 Mar. 2017
    Field experiments of turbulent velocities were conducted in order to reveal Langmuir circulation, a potential ingredient of ocean surface mixing. Coherent structures of Langmuir circulation were successfully captured in our field experiments. Observed turbulence was intense when surface waves, a driver of Langmuir circulation, were strong, while its intensity was also affected by surface heat flux. We also find that wind forcing play an important role in Langmuir turbulence when wind and wave are misaligned. Numerical experiments support these observed features. These results indicate that Langmuir turbulence mixes ocean surface strongly when surface waves are intense, but associated mixing properties are highly dependent on wind and wave directions.

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