WARM-SEASON EFFECTS OF THE GULF-STREAM ON MESOSCALE CHARACTERISTICS OF THE ATMOSPHERIC BOUNDARY-LAYER

The meteorological regime off the coast of North Carolina exhibits lit tle 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 circulatio ns are dominant. One such circulation develops in response to the sea surface temperature discontinuity between the Gulf Stream and the rela tively cooler water of the Continental Shelf. When synoptic conditions are favorable, differences in surface fluxes of heat and moisture acr oss this discontinuity cause the development of an ageostrophic soleno idal circulation and the creation of an atmospheric boundary layer con vergence zone. This resulting frontal zone, or Gulf Stream atmospheric front (GSAF), is a commonly observed feature in this region during th e warm season. Simulations using The Pennsylvania State University-Nat ional Center for Atmospheric Research mesoscale model are combined wit h 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 wa s given to determining whether a model with resolution and physics sim ilar to those of operational mesoscale forecast models can adequately predict this phenomenon. Although limitations in the horizontal and ve rtical resolution of the model prevent detailed reproduction of the me so-gamma-scale structure of the GSAF, the model does produce a signifi cant meso-beta boundary layer convergence zone in response to the loca l SST maximum associated with the Gulf Stream. The magnitude of the mo deled response is primarily a function of air-sea temperature differen ce, the local wind vector, and the depth of the boundary layer.