Warm-Season Effects of the Gulf Stream on Mesoscale Characteristics of the Atmospheric Boundary Layer

Abstract

The meteorological regime off the coast of North Carolina exhibits little synoptic-scale baroclinity during the summer months. As a result, the large-scale atmospheric forcing in this region is frequently weak. Given this weak synoptic forcing, mesoscale boundary layer circulations are dominant. One such circulation develops in response to the sea surface temperature discontinuity between the Gulf Stream and the relatively cooler water of the Continental Shelf. When synoptic conditions are favorable, differences in surface fluxes of heat and moisture across this discontinuity cause the development of an ageostrophic solenoidal circulation and the creation of an atmospheric boundary layer convergence zone. This resulting frontal zone, or Gulf Stream atmospheric front (GSAF), is a commonly observed feature in this region during the warm season. Simulations using The Pennsylvania State University–National Center for Atmospheric Research mesoscale model are combined with data gathered from the High-Resolution Remote Sensing Experiment to study the effects of the Gulf Stream on mesoscale circulations in the warm-season marine atmospheric boundary layer. Particular attention was given to determining whether a model with resolution and physics similar to those of operational mesoscale forecast models can adequately predict this phenomenon. Although limitations in the horizontal and vertical resolution of the model prevent detailed reproduction of the meso-γ-scale structure of the GSAF, the model does produce a significant meso-β boundary layer convergence zone in response to the local SST maximum associated with the Gulf Stream. The magnitude of the modeled response is primarily a function of air–sea temperature difference, the local wind vector, and the depth of the boundary layer.