Analysis of wind data in the low atmosphere from a RASS sodar

摘要

This paper focuses on the ability of a sodar to describe somecharacteristics of the atmospheric vertical structure and presents sometechniques for meteorological data evaluation. The measuring campaign tookplace in April 2001 and consisted of 10-min averages covering the loweratmosphere from 40 to 500 m at 20-m levels. Three methods were considered,the first of which was a scalar analysis performed using a combination ofwind and temperature median profiles. A noticeable contrast between day andnight was obtained. Flat wind profiles during the day were a consequence ofprevailing convective conditions that determined thermal turbulence. Astable layer above 260 m capped the unstable layer situated below andguaranteed the stability of the boundary layer. During the night, thepresence of a low level jet was the most significant feature. The height ofthe core was 340 m and the higher vertical winds defined it clearly. Thesecond method focused on the wind vector. In this analysis, theanti-cyclonic rotation of hourly averages was considered in the lower levelswhere it was observed. After a translation of the origin, an empirical,robust model with two parts was then proposed for the resulting vector. Theangle was described linearly and the module by a second order model forcylindrical data. Finally, as a third method, three regression analyses wereinvestigated: vectorial, taking every wind component separately and scalar.The two first seemed to be more complete due to their description ofanti-cyclonic wind rotation when height increased. Correlation coefficientsalso proved to be more satisfactory. As a consequence, these techniques,although less frequently used, are more suitable to study wind in the lowatmosphere.