ESRL/PSD Seminar Series

Abstract

The response of the atmospheric boundary layer to fronts of sea surface temperature (SST) is characterized by an increase of wind speed over warm SST, and correlations between divergence and curl of the wind stress and the down- and crosswind components of the SST gradient, respectively. The associated regression (or coupling) coefficients for the wind stress divergence are consistently larger than those for the wind stress curl. To explore the underlying physics, we introduce a linear model of the atmospheric boundary response to SST fronts in the presence of background advection. The model includes modulation by gradients of SST of boundary layer hydrostatic pressure and vertical mixing, and of the impact of secondary circulations on the stratification outside of the boundary layer. The model solutions are a strong function of the scale of the SST and the background advection, and recover observed characteristics. The coupling coefficients for wind stress divergence and curl are governed by distinct physics. The former is dominated by lee gravity waves and thermally direct 'sea-breezes', while the latter is governed by geostrophic spin-down in the presence of advection of potential vorticity