Observations of systematic boundary layer divergence patterns and their relationship to land use and topography

Data from several surface meteorological networks in the vicinity of the U. S. Department of Energy's Southern Great Plains Cloud and Radiation Testbed were used to investigate the relationship between boundary layer circulati ons, as reflected in composited divergence fields, and variations in vegeta tion, surface temperature, and topography. The study is unique in using dat a from a dense collection of surface meteorological instruments that are di stributed over a region comparable in size to a GCM grid cell in a region o f sharply varying land use. These land use differences provide variations i n surface heat flux on a scale O(100 km) that has been postulated to produc e the strongest surface-induced mesoscale circulations in the boundary laye r. This paper details the first signature in data of a boundary layer circu lation that can be attributed to land use differences at this scale. It is found, however, that in the composited fields the majority of the divergenc e extrema persist over seasons, are present in all observed wind conditions , are geographically fixed, and are more likely related to gentle topograph ic features rather than to land use differences.