Observations of the turbulent kinetic energy dissipation rate in the upper central South China Sea
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Measurements of the turbulent kinetic energy dissipation rate (ε), velocity, temperature, and salinity were obtained for the upper ocean of the central South China Sea (14.5° N, 117.0° E) during an experimental campaign from May 11 to 13, 2010. Dissipation in the diurnal mixed layer showed a diurnal variability that was strongly affected by the surface buoyancy flux. Dissipation was enhanced (ε ∼ 10−7 W kg−1) at night due to the convective mixing and was weakened (ε ∼ 10−9 W kg−1) in daytime due to the stratification. Dissipation in the thermocline varied with time under the influence of internal waves. Shear from high-frequency internal waves (period ∼8 h) played an important role in enhancing the turbulent mixing in the thermocline. In the period of strong high-frequency internal waves, the shear from high-frequency internal waves became strong and the depth-averaged ε in the thermocline was elevated by almost one order of magnitude. Compared with the dissipation in the thermocline, dissipation below was weaker (the time-averaged ε ∼ 10−10 W kg−1). The observation indicates that the dissipation rates during the measurements can be parameterized by the MacKinnon-Gregg model that is widely used in the continental shelf but are not in agreement with the Gregg-Henyey model used for the open ocean.
KeywordsDissipation rate Surface buoyancy flux Internal wave Parameterization
This work is supported by the National Natural Science Foundation of China: 41630970, 41376022, 41676022, and 41521005. The data we used is from South China Sea Institute of Oceanology.
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