09:30 〜 09:45
[AOS09-02] A new parameterization of turbulent mixing caused by tidal flow over abyssal rough bathymetry
キーワード：潮汐混合、深海底凹凸地形、パラメタリゼーション、内部潮汐波、内部風下波、三波共鳴干渉
It is believed that tidal interaction with abyssal rough bathymetry can create mixing hotspots extending upward from the ocean bottom. Although there exist parameterizations of bottom-enhanced tidal mixing, they do not take into account that the internal waves generated by tide-topography interactions transform from internal tidal waves to quasi-steady internal lee waves as kHU0 /ω increases and exceeds unity (kH is the horizontal wavenumber of the bottom topography; U0 is the amplitude of the tidal flow; ω is the tidal frequency) (Mohri et al., 2010).
In this study, we formulate a new parameterization of tidal mixing over abyssal rough bathymetry in which the vertical decay scale of the energy dissipation rate (ε) is estimated by multiplying the theoretically obtained vertical group velocity of the internal tidal wave or the quasi-steady internal lee wave by the time scale of its nonlinear interaction (induced diffusion) with the background Garrett-Munk (GM) internal wave field (McComas and Müller, 1981). The resulting parameterization explicitly shows that the vertical decay scale of ε becomes independent of U0 but inversely proportional to kH squared when kHU0 /ω < 1 and independent of kH but proportional to U0 squared when kHU0 /ω > 1.
It is confirmed that the formulated parameterization predicts the vertical distribution of ε in agreement with that obtained from the eikonal calculation for the internal tidal wave or the quasi-steady internal lee wave propagating from the ocean bottom up into the background GM internal wave field (Iwamae et al., 2009; Hibiya et al., 2017).
In this study, we formulate a new parameterization of tidal mixing over abyssal rough bathymetry in which the vertical decay scale of the energy dissipation rate (ε) is estimated by multiplying the theoretically obtained vertical group velocity of the internal tidal wave or the quasi-steady internal lee wave by the time scale of its nonlinear interaction (induced diffusion) with the background Garrett-Munk (GM) internal wave field (McComas and Müller, 1981). The resulting parameterization explicitly shows that the vertical decay scale of ε becomes independent of U0 but inversely proportional to kH squared when kHU0 /ω < 1 and independent of kH but proportional to U0 squared when kHU0 /ω > 1.
It is confirmed that the formulated parameterization predicts the vertical distribution of ε in agreement with that obtained from the eikonal calculation for the internal tidal wave or the quasi-steady internal lee wave propagating from the ocean bottom up into the background GM internal wave field (Iwamae et al., 2009; Hibiya et al., 2017).