Turbulent Kinetic Energy Production in a Far‐Field River Plume Under Upwelling‐Favorable Winds

Abstract

An idealized three‐dimensional numerical model is used to investigate turbulent kinetic energy (TKE) production in a far‐field river plume under upwelling‐favorable winds. TKE production decreases over longer length scales as the river plume thickens. Maximum TKE production appears in the surface layer and is mainly generated by the alongshore component of the velocity shear. The large velocity shear and weak stratification in the surface layer result in a gradient Richardson number (Ri) of <0.25, which corresponds to the locally high TKE production. We find that asymmetrical TKE production occurs at the two edges of the river plume, due to the opposite nonlinear interaction of the Ekman and geostrophic effects at the shoreward and seaward edges of the river plume. This asymmetrical TKE production combines with secondary upwelling circulation in the river plume under upwelling‐favorable winds, which may generate more intense biological activity at the shoreward edge of the river plume than at the seaward edge. Numerical model experiments are performed to examine the effects of wind, river discharge, and stratified conditions on TKE production in the river plume. Finally, we propose a conceptual model in which the depth‐averaged TKE production in the river plume is proportional to the alongshore wind stress (τy2.5 ${{\tau }_{y}}^{2.5}$) and inversely proportional to the cube of the surface boundary layer thickness (D3), which is consistent with the results of numerical experiments.