海琴论坛预告第13期（2）：中国东海和孟加拉湾浅水海洋边界层的小尺度动力学研究

报告简介：

Small-scale dynamical processes (Internal waves and turbulence) play a crucial role in understanding and quantifying ocean mixing that influence on bio-geochemical property exchanges in ocean boundary layers and interior waters. Our investigation focused on turbulence and internal wave generation (IW) in the bottom and surface boundary layers (BBL), seasonal pycnoclines of the East China Sea (ECS) and Bay of Bengal (BoB) using a suite of modern instrumentation.

The ECS is a shallow sea, where episodes of strong, high-frequency velocity oscillations were recorded over the entire water column. In this study, we delineate a link between IW episodes in different phases of the barotropic tide. Apart from that BBL dynamics is also explored. Velocity profiles in the BBL contained segments of different length that can be well-fitted to the classic log-layer formula. The friction velocity so deduced, however, appears to be unreasonably high, leading to anomalously high drag coefficients. Similar inferences were made by fitting velocity data to Coles’ log-wake model, although in some cases the model-data fit was excellent. The measurements of turbulent kinetic energy dissipation rate show a significant disagreement with those predicted by the log-layer formula. A more acceptable friction velocity magnitude could be obtained via a Perlin’s modified log-layer model that accounts for density stratification in BBL.

The measurements taken in the Bay of Bengal (BoB) and associate waters around Sri Lanka in 2013 and 2014were used to study turbulence in the upper oceanic layer influenced by monsoon. Filaments and lenses of diluted surface low-saline water led to active frontogenesis. Below low-salinity lenses, the turbulence was readily damped, due to high local stratification that suppresses vertical mixing. Turbulence in the surface layer quickly reacted to the changes of the wind stress. Stirring of horizontal gradients of salinity/density affected entrainment at the pycnocline, and hence the deepening of the mixed layer.