The Interactive Evolution of the Oceanic and Atmospheric Boundary Layers in the Source Regions of the Trades

Abstract

Subtropical status tends to form over relatively cold water, its presence then keeps the water cold. We have investigated the resultant downstream development in the framework of an interactive, two-dimensional, steady-state model of the oceanic and atmospheric mixed layers. Upstream boundary and interior conditions in both media, and irradiance and advection velocities are specified; mixed-layer temperature salinity, heat and moisture content are evolving dependent variables. The integration is continued downstream until convective instability develops or, failing that, for a distance of 2000 km. Sensitivity tests show this development to be strongly affected by the upstream boundary conditions, implying an effect of coastal upwelling processes upon oceanic and atmospheric temperature profiles for a long distance downstream. The dependence on the advection velocity is very nonlinear. The amplitude of temperature changes is of the same order in both media, despite the greater oceanic heat capacity. This is due to the unequal advection rate, which causes a water column to remain in the affected area some fifty times longer than the air above.