동중국해 난류 소산률 관측

Abstract

The East China Sea (ECS) and the adjacent seas are one of the most important regions for internal wave generation and associated turbulence mixing. These aspects provide a good opportunity to comprehensive understanding of internal waves and turbulence. We measured turbulence structure in the ECS with strong tidal motion during a focused field campaign in August, 2005, using a modern microstructure profiler Turbomap. The Turbomap measurements were conducted at 31 survey stations and 57 profiles were also obtained at a station every 6 minutes on average. The microstructure profiler measures micro-scale velocity shear and temperature, as well as conventional CTD variables (conductivity, temperature and pressure). The turbulent energy dissipation rate shows remarkable differences in vertical structure, ranging from 10-9 to 10-5 W/kg. In the thermocline, the dissipation rate with average value of 10-7 W/kg follows closely the pycnocline displacements caused by internal waves. It was also observed that episodic intrusions of enhanced near-bottom turbulence into the upper layers, which are probably related to the tidal cycle in the region. Vertical eddy diffusivity is generally around 10-3 m2/s. Near bottom, it reaches to 10-1 m2/s due to both of weak stratification and strong dissipation rate. We found that vertical eddy diffusivity is inversely proportional to squared buoyancey frequency, while there is no clear relation between turbulent energy dissipation rate and squared buoyancey frequency.