Summertime low-level jet characteristics measured by sodars over rural and urban areas

Abstract

This work is devoted to the study of nocturnal low-level jet streams (LLJ) at altitudes up to 400 m agl, with the help of Doppler sodars. The objective was twofold: firstly, to study the origin and behavior of LLJ in a mid-latitude region, and secondly, to compare the LLJ characteristics over urban and rural areas. To this end, simultaneous measurements of wind velocity profiles over the center of Moscow city and over a nearby countryside were carried out. The sodar data on wind speed and direction collected continuously during 27 days in July 2005 were analyzed together with in situ data from a meteorological mast. A good correlation between the height of the LLJ core and the inversion height was found. Empirical distributions of the maximum speed of the jet streams, the height of the jet core, and the wind turning across the stream were obtained. The relationships between the LLJs characteristics and some surface layer parameters were found. Over the urban area the jet streams appeared less frequently and at heigher altitudes than over the countryside.