Boundary Layer Characteristics over Areas of Inhomogeneous Surface Fluxes

Abstract

This paper describes results from a June 1992 field program to study the response of the boundary layer over a site with well-defined extreme differences in sensible and latent heat fluxes over clearly separated areas, each with characteristic length scales of 10 km or more. The experiment region consisted of semiarid grassland steppe and irrigated farmland. Sensible heat flux maxima over the steppe regularly reached values in excess of 300 W m−2 and were typically a factor of 4 or more greater than those over the farmland. Two days were selected for analysis: one with moderate winds of 7–10 m s−1 and one with lighter winds of 4–7 m s−1 over the steppe. In both cases the wind directions were nearly perpendicular to the boundary between the steppe and farm. An analysis of potential temperature soundings showed that mixed-layer characteristics over both the farm and the steppe were largely determined by heating over the steppe, with advection from the steppe to the farm playing a significant role. ... Abstract This paper describes results from a June 1992 field program to study the response of the boundary layer over a site with well-defined extreme differences in sensible and latent heat fluxes over clearly separated areas, each with characteristic length scales of 10 km or more. The experiment region consisted of semiarid grassland steppe and irrigated farmland. Sensible heat flux maxima over the steppe regularly reached values in excess of 300 W m−2 and were typically a factor of 4 or more greater than those over the farmland. Two days were selected for analysis: one with moderate winds of 7–10 m s−1 and one with lighter winds of 4–7 m s−1 over the steppe. In both cases the wind directions were nearly perpendicular to the boundary between the steppe and farm. An analysis of potential temperature soundings showed that mixed-layer characteristics over both the farm and the steppe were largely determined by heating over the steppe, with advection from the steppe to the farm playing a significant role. ...