It is believed that the global thermohaline circulation is stronglyinfluenced by small-scale ocean mixing processes. Munk and Wunsch (1998) found that the spatially averaged diapycnal diffusivity of 10-4 m2s-1 is required in the deep ocean to support the thermohaline circulation. In order to reproduce diapycnal diffusivity of order 10-4m2s-1, the power required is about 2.1 TW (1 TW = 1012 W) which is believed to be provided by internal tides as well as wind stress fluctuations (Munk and Wunsch, 1998). Nevertheless, in contrast to the global energy flux from internal tides which is estimated to be about 0.9 TW based on astronomical measurements (Munk, 1997; Munk and Wunsch, 1998), direct estimate of the global energy flux from wind stress fluctuations has not been made.
In the present study, based on a simple numerical model, the annual mean global energy flux to inertial motions in the surface mixed layer is estimated to be about 0.7 TW. This value is about half of the previous estimate by Munk and Wunsch (1998) (1.2 TW) and is comparable to the global estimate of the energy flux from internal tides (0.9 TW). The annual mean global energy flux from internal tides and wind stress fluctuations then sums up to 1.6 TW, obviously falling short of the value required to satisfy the large-scale advective-diffusive balance of the meridional overturning circulation.
The present study indicates that some additional mechanism such aseffects of Ekman upwelling in the Southern Ocean (Webb and Suginohara, 2001) should also be taken into account to sustain the large-scale thermohaline circulation. |
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