On wind-driven mixed layers with strong horizontal gradients - a theory with application to coastal upwelling.

Abstract

A theory of a two dimensional wind driven diabatic ocean mixed layer with strong horizontal gradients is formulated analytically. An equation that allows the relaxation of the strict Ekman balance - Coriolis force against wind stress - is derived from a careful consideration of the cross gradient momentum balance. The relaxation scale depends implicitly on mixed layer depth and density distributions, which themselves are determined by mixing entrainment and diabatic processes, and in simple situations reduces to the familiar baroclinic Rossby radius of deformation. When mixed layer depth or density contrast at the mixed layer base becomes small, this relaxation scale becomes small and characterizes the width of high gradient front like features in the mixed layer. (from authors' abstract)