PNNL

Abstract

We have used data from several surface meteorological networks in the vicinity of the U.S. Department of Energy's Southern Great Plains Cloud and Radiation Testbed (CART) to investigate the relationship between boundary layer circulations, as reflected in composited divergence fields, and variations in vegetation, surface temperature, and topography. The study is unique in using data from a dense collection of surface meteorological instruments that are distributed over a region comparable in size to a GCM grid cell in a region of sharply varying land use. These land use differences provide variations in surface heat flux on a scale O(100 km) that has been postulated to produce the strongest surface-induced mesoscale circulations in the boundary layer. We have found what we believe to be the first signature in data of a boundary layer circulation that can be attributed to land use differences at this scale. We have also found, however, that in our composited fields the majority of the divergence extrema persist over seasons, are present in all observed wind conditions, are geographically fixed, and are more likely related to gentle topographic features rather than to land use differences.