Wave-current interaction in the ocean surface layer; New perspective in its dynamics and global evaluation of resultant mixing

2021 Fiscal Year Final Research Report

• Project/Area Number: 19H01968
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Basic Section 17020:Atmospheric and hydrospheric sciences-related
• Research Institution: Kyoto University
• Principal Investigator: Yoshikawa Yutaka 京都大学, 理学研究科, 教授 (40346854)
• Co-Investigator(Kenkyū-buntansha): 馬場 康之 京都大学, 防災研究所, 准教授 (30283675)
• Project Period (FY): 2019-04-01 – 2022-03-31
• Keywords: 波と流れの相互作用 / 海洋表層混合 / 波解像数値実験

Outline of Final Research Achievements

Wave-induced turbulence in the ocean surface layer, one of major sources of prediction errors in recent climate simulations, was investigated using the wave-resolving numerical model. In this model, waves and turbulence can be resolved simultaneously without parameterization. Simulations show that the non-breaking surface waves induce mixing even without surface wind. Mechanics and properties of the mixing observed in the simulations were quantified. Vorticity budget analysis reveals that the non-breaking wave-induced mixing without surface wind is caused by secondary circulations generated by rectified vorticity stretching/shrinking/tilting by the waves, as the non-breaking wave-induced mixing with surface waves is. Eddy diffusivity due to the surface waves was also quantified as a function of wave length and amplitude.

Free Research Field

海洋力学

Academic Significance and Societal Importance of the Research Achievements

海面の波による乱流混合の影響を正しく表現することは、現状の気候モデルの精度向上に大きく貢献すると期待されている。これまで二つの説で別々に説明されていた波による混合の機構を、波による指向性のある渦の伸縮と傾斜として統一したことにより、今後行われるべき混合の定式化に道筋をつける結果となった。また、波の波長や振幅を変えた実験の結果は、定式化を構築する際の基盤となる資料として有用である。今後の波による混合の定式化と、それを組み込んだ気候モデルの予測・再現精度向上が期待される。