On Height of the Surface Air Layer by Sodar Data

Abstract

Average empirical estimations of the surface air layer height in Moscow have been received by the data of long-term acoustic remote sensing of the atmosphere using the MODOS Doppler sodar (METEK, Germany). Based on the assumption that the average conditions are close to neutral stratification, this height, as the top of the quasi-linear section of the average long-term wind velocity profile in semilogarithmic coordinates, is 40–60 m. The wind rotation height, i.e., the height of intersection of day and night wind profiles, is 95 m per year on average. The roughness length in conditions of loosely packed but high urban development in the vicinity of Moscow State University in Moscow is 5 m. According to the criterion of the constant wind direction in the surface air layer, its height manifests itself in the monthly average wind direction profiles over the “dead zone” of the sodar (40 m) in approximately one out of three cases and usually amounts to 60 m (less often 80 or 100 m). In all other cases, it is apparently masked by the dead zone. According to this approach, the average height of the surface layer is probably a little less than 50 m, which is close to the estimate obtained from the logarithmic distribution of wind velocity with height in this layer. The daily variation of the surface air layer height is noted by the largest values in the afternoon (80–100 m in summer under conditions of prevailing unstable stratification and 60–80 m in winter) and the smallest ones (less than 40 m) in the late evening and at night in summer and from evening to noon in winter.