Energetics of wind-induced turbulent mixing in the ocean |
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| Authors: | Michio Watanabe Toshiyuki Hibiya |
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| Institution: | (1) Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, Tokyo 113-0033, Japan;(2) Present address: Center for Climate System Research, The University of Tokyo, Chiba 277-8568, Japan |
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| Abstract: | The pattern and magnitude of the global ocean overturning circulation is believed to be strongly controlled by the distribution
of diapycnal diffusivity below 1000 m depth. Although wind stress fluctuation is a candidate for the major energy sources
of diapycnal mixing processes, the global distribution of wind-induced diapycnal diffusivity is still uncertain. It has been
believed that internal waves generated by wind stress fluctuations at middle and high latitudes propagate equatorward until
their frequency is twice the local inertial frequency and break down via parametric subharmonic instabilities, causing diapycnal
mixing. In order to check the proposed scenario, we use a vertically two-dimensional primitive equation model to examine the
spatial distribution of “mixing hotspots” caused by wind stress fluctuations. It is shown that most of the wind-induced energy
fed into the ocean interior is dissipated within the top 1000 m depth in the wind-forced area and the energy dissipation rate
at low latitudes is very small. Consequently, the energy supplied to diapycnal mixing processes below 1000 m depth falls short
of the level required to sustain the global ocean overturning circulation. |
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| Keywords: | Turbulence diffusivity and mixing processes internal and inertial waves numerical modeling upper ocean and mixed layer processes |
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