Vertical mixing observed on the continental slope of the southwestern East/Japan Sea

Abstract

Over the southwestern East/Japan Sea, 25 hours long hourly CTD, and a free falling microstructure profiler (TurboMAP) data were obtained during a spring and neap tidal period. Vertical diffusivities estimated density inversion from CTD profiles using the Thorpe scale, and shear from the microstructure profiler are compared. When converting the Thorpe scale into the diffusivity two different mixing efficiency parameterizations were utilized. One is a widely used method proposed by Osborn (1980) in which the functional form is independent of turbulent intensity. The other is relatively recent one by Shih et al. (2005) in which the functional form is dependent on turbulent intensity. Both methods produce similar vertical structure, but the one based on Shih et al. (2005) is smaller than that based on Osborn (1980), The diffusivity estimated from microstructure measurement below the main thermocline was much greater during the spring tidal period (5.5e-4(Osborn), 9.2e-5(Shih) m2/s) than the neap (2.6e-4(Osborn), 5.3e-5(Shih) m2/s) suggesting internal tide induced mixing.