Large-eddy simulation of the oceanic mixed layer showed that Langmuir circulation (LC) is weakened under the surface heating and is ultimately broken down if the intensity of the surface heating becomes sufficiently strong. The critical condition for the breakdown of LC was mainly determined by the Hoenikker number Ho, and the transition occurs in the range Ho ∼ 1-2. The breakdown of LC leads to a drastic change in the characteristics of the oceanic mixed layer, such as the variation of the rms horizontal velocities with time, the ratio of the horizontal spectra of vertical velocity field, and the pitch. The stability condition for LC suggested by Leibovich was still observed in this simulation. Furthermore, it was found that LC is largely responsible for the formation of a thermocline and the maintenance of a well-mixed layer above it, and the depth of a thermocline was estimated in that case.
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