[A-OS24] Exploring new frontiers of oceanic mixing research in the next decade

[AOS24-05] A new parameterization of tidal mixing enhanced over rough seafloor topography

*日比谷 紀之¹ (1.東京大学大学院理学系研究科地球惑星科学専攻)

キーワード：パラメタリゼーション、乱流散逸率、鉛直減衰スケール、潮汐流、深海凹凸地形、内部風下波

It is believed that tidal interaction with rough seafloor topography can create mixing hotspots extending off the seafloor. Although there exist fine-scale parameterizations of tidal mixing enhanced over rough seafloor, they do not reflect the fact that the internal waves emanating from rough seafloor transform from internal tidal waves to internal lee waves as tide-seafloor interaction strengthens with k_HU₀ /ω exceeding unity where k_H is the dominant horizontal wavenumber of rough seafloor, U₀ is the amplitude of tidal flow, and ω is tidal frequency. Taking into account this fact, we formulate here the vertical decay scale of energy dissipation rates over rough seafloor by multiplying the theoretically obtained vertical group velocities of internal lee waves by the time scale of their nonlinear interaction with the background Garrett-Munk internal wave field. The resulting formulation explicitly shows that the vertical extent of mixing hotspots over rough seafloor becomes independent of k_H but proportional to U₀ squared, which agrees very well with the results of eikonal experiments and consistent with the available data from the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES).