Are Radiosonde Time Scales Appropriate to Characterize Boundary Layer Wind Profiles?

Abstract

One approach under investigation for obtaining regional-scale surface fluxes of water vapor, heat, and momentum from complex terrain involves the applicability of flux-profile relationships in the atmospheric boundary layer (ABL). Mean humidity, temperature, and wind speed profiles in the ABL can be measured by means of radiosondes. A disadvantage, however, of this method is the relatively quick passage of the sonde through the ABL compared to the characteristic time scales or memory of the turbulence. Remote sensing with sodar (Sound Detection and Ranging) allows the measurement of mean wind profiles over time scales which are perhaps more appropriate for the turbulence. Wind profiles measured by both radiosondes and sodar over the Landes Forest in southwestern France, as part of the HAPEX-MOBILHY experiment, are compared under conditions of neutral stability. The sodar wind profiles were measured by a team from the CRPE (Centre de Recherches en Physique de l'Environnement, Saint-Maur-des-Fossés/Issy-les-Moulineaux, France); the sodar measurements were taken over 15-min periods. The lower limit of the inner region of the ABL was found to be the same for both sets of profiles. Approximately the same regional scale surface roughness was obtained with both types of sounders, namely z0 = 1.2 m; the corresponding shear stresses derived from both sets of profiles were well correlated.