Wind Direction and Equilibrium Mixed Layer Depth: General Theory

Abstract

A usually neglected Coriolis term in the turbulent kinetic energy budget of the ocean surface mixed layer is examined for the special case of a steady-state mixed layer depth with no entrainment. In this term, the Reynolds stresses interact with the northward component of planetary rotation to exchange turbulent kinetic energy between horizontal and vertical components. The direction of the exchange depends upon the sign of east-west component of the wind stress. A vertically integrated or bulk theory is derived for a non-entraining mixed layer in equilibrium. The results show that the vertical turbulent kinetic energy and hence the vertical mixing and mixed layer depth will be reduced for westerly winds. Fasterly winds will increase vertical mixing and mixed layer depth.