日本地球惑星科学連合2018年大会

講演情報

[EE] Eveningポスター発表

セッション記号 A (大気水圏科学) » A-OS 海洋科学・海洋環境

[A-OS11] What we have learned about ocean mixing in the last decade

2018年5月21日(月) 17:15 〜 18:30 ポスター会場 (幕張メッセ国際展示場 7ホール)

コンビーナ:日比谷 紀之(東京大学大学院理学系研究科地球惑星科学専攻)、Louis St Laurent (Woods Hole Oceanographic Institution)、Ren-Chieh Lien(None、共同)、Robin Ann Robertson (Xiamen University Malaysia)

[AOS11-P05] Observed variations in mixing efficiency in the deep ocean

*伊地知 敬1日比谷 紀之1 (1.東京大学大学院理学系研究科)

キーワード:乱流混合

Recent progress in direct numerical simulations (DNS) of stratified turbulent flows has led to increasing attention to the applicability of the constant mixing coefficient Γ in the Osborn’s eddy diffusivity model, Γ = 0.2. Motivated by lack of observational estimates of Γ particularly in the deep ocean, this study examines variations of Γ using deep microstructure profiles collected in various regions of the North Pacific and the Southern Ocean. It is shown that Γ is not constant but varies significantly with the ratio of the Ozmidov scale to the Thorpe scale ROT in a fashion similar to that obtained by previous DNS studies. Efficient mixing events with Γ ~ O(1) and ROT ~ O(0.1) tend to be frequently observed in the deep ocean, while moderate mixing events with Γ ~ O(0.1) and ROT ~ O(1) tend to be observed in the upper ocean. Furthermore, the observed negative relationship between Γ and ROT is consistent with a simple scaling Γ proportional to ROT−4/3 that can be derived from classical turbulence theories. In contrast, the observed results exhibit no definite relationships between Γ and the buoyancy Reynolds number Reb, although Reb has long been thought to be another key parameter controlling Γ.