A study on meiyu boundary layer characterstics over dongshan china using wind profiler radar

In order to understand the formation mechanism and vertical structure of precipitating cloud systems associated with the Meiyu/Baiu frontal cyclone, special observational campaigns have been conducted in the downstream of the Yangtze River during June-July 2001 and 2002. We deployed a Lower Atmospheric Wind Profiler (LAWP) with Radio Acoustic Sounding System (RASS) at the Meteorological Observatory, Dongshan, China to observe the inner structure of precipitating cloud systems seen frequently in the observational area. The LAWP provides vertical profiles of three-dimensional wind, convective boundary layer (CBL) and temperature from the lower atmosphere with a height resolution of 58 m to 202 m and a time resolution of about 1 to 60 minutes. LAWP had been operated in two modes: low mode and high mode up to 4 km and 11 km height during non-rainy and rain conditions, respectively. A study was carried out during intensive observational period 2002 (IOP-2002) to understand the pre-convective environments in the boundary layer during pre-Meiyu and Meiyu convective days to find out whether there is any precursor before the convection triggering. The LAWP observations demonstrate that during Meiyu period the average CBL is below < 1 km and whereas, pre- and post-Meiyu period the average CBL height above 1 km. The results show that distinguishable CBL evolution was noticed during pre-Meiyu and Meiyu period. LAWP observed eleven precipitating cloud systems in the vicinity of Meiyu frontal zone during IOP-2002. Each precipitating cloud system was divided into three rain types: convective, mixed convective-stratiform, and stratiform rain based on the LAWP observation data from the echo intensity above melting layer and the difference of the fall speed of precipitation particles between 3 and 6 km altitude. In the passage of the cloud system, convective systems embedded within a wide stratiform precipitation were observed. The observed precipitating cloud systems showed a diurnal variation with a peak in the late evening and nighttime. Boundary layer winds often shows strong South/southwesterly flow when the Meiyu precipitating cloud systems passes overhead of the LAWP.