Sensitivity of the surface equatorial ocean to the parameterization of vertical mixing

Abstract

A new high-resolution, numerical model of a zonally independent equatorial channel helps to explore this question and includes three parameterizations, all of which increase mixing for decreasing Richardson numbers. The meridional and vertical velocity fields in the surface layer are very sensitive to the strength of mixing implied by the different parameterizations. For the smooth Richardson number dependence of the eddy coefficients, equatorial upwelling due to easterly winds reaches the surface. The dramatically increasing eddy coefficients for small Richardson numbers yield reduced equatorial upwelling rates in the surface layer. The diagnostic adjustment of the Richardson number shows in the surface layer close to the equator reversed meridional shear and downwelling in response to easterly winds! A simple model for the low-latitude wind current in the presence of horizontal density gradients reproduces this reversal of the meridional and vertical flows. -from Authors