Observations of the turbulent kinetic energy dissipation rate in the upper central South China Sea

Abstract

Measurements of the turbulent kinetic energy dissipation rate (e), 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 (e ∼ 10−7 W kg−1) at night due to the convective mixing and was weakened (e ∼ 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 e 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 e ∼ 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.