Shallow Great Lake–Scale Atmospheric Thermal Circulation Imaged by Synthetic Aperture Radar

Abstract

Synthetic aperture radar (SAR) has proven to be a useful tool for observing a wide variety of oceanographic and atmospheric phenomena. This is because capillary waves whose amplitudes are modulated in space and time by oceanic and atmospheric processes are efficient scatterers at SAR wavelengths. In this paper, a SAR image of Lake Michigan taken during the Lake-Induced Convection Experiment is analyzed. The image shows three broad parallel bands identifiable as the components of a shallow, Great Lake?induced thermal circulation:two bands associated with opposing land-breeze circulations, and a middle band containing the signature of boundary layer convection. A cross-frontal cut shows that the width of the two land-breeze fronts varies in a manner consistent with previously reported observations of land and sea breezes superimposed on synoptic flows. The SAR image analysis in conjunction with a mesoscale analysis of a Great Lake?scale convection pattern substantially increases the available knowledge of that pattern. Specifically, the SAR image provides information concerning the precise placement of the surface land-breeze fronts not available from other means. Finally, the SAR analysis shows that the western land-breeze brightness patterns are affected by the shallow terrain along the western shore of Lake Michigan. The latter point therefore suggests that SAR can provide valuable information about the link between variations in surface roughness and/or land use patterns and the horizontal structure of the surface wind stress over coastal regions.