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Advanced Taiwan Ocean Prediction System

Tseng, Tsu-Lun - ALL News | 2020-06-04 | Count:82


Title: Dynamics and Variability of Topography-induced Shear Instabilities in Western Boundary Currents


Shear instability is one of the most important turbulence generation mechanisms in the ocean, in which flow instabilities develop in stratified shear flows and dominate the flow dynamics and mixing. Proper parameterization of small-scale physical processes is required in large-scale ocean models because the horizontal grid resolution (O(km)) in these models is typically much greater than the size of instability waves. The accurate prediction of shear instabilities and the corresponding mixing efficiency can improve model accuracy of the large-scale circulation and transport in the ocean. Therefore, studies on small-scale processes, for example, shear instabilities, provide insight on turbulent mixing processes in the ocean. The properties of shear instabilities, such as the length scales in both horizontal and vertical directions and the frequency, are of key interest in determining the mixing efficiency. A high resolution model with Large Eddy Simulation (LES) closure is applied to investigate the dominant mechanism controlling the scale of shear instabilities in stratified shear flow at high Reynolds Number (Re ~ O(105)). Model experiments indicate the criterion of Froude number (Fr=U/NL) for the characteristic scales of instability waves. The analyses of model experiment and direct measurements of turbulence suggest that the period of instability waves strongly depend on the Froude number and high turbulence is mainly populated in the forward inclined, asymmetric, cusp-like bands.

Keywords:  shear instability, mixing, direct measurements of turbulence, LES model


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