Diurnal and Seasonal Variations of Boundary-Layer Structure Observed with a Radar Wind Profiler and RASS

Abstract

A wind profiler-radio acoustic sounding system at Denver collected hourly wind and virtual-temperature data through the boundary layer in the latter half of 1989. Analyzed monthly averages of 24-h time-height cross sections of the daily measurements show a number of significant features. The growth of the nocturnal temperature inversion is observed, followed by a rapid transition to a deep daytime mixed layer. The progression from a strong diurnal temperature signal in the summer to weak diurnal variability in the winter is documented. A mean upslope wind component is found in the middle-to-late afternoon in the summer and autumn months, with a reverse, return flow aloft. Boundary-layer winds show a strong inertial oscillation, with the phase closely following the diurnal heating cycle. Perturbation winds in the return-flow region aloft oscillate almost 180° out of phase with the boundary-layer winds.