Tuesday, 25 October 2005
Alvarado F and Atria (Hotel Albuquerque at Old Town)
To understand the formation mechanism and vertical structure of precipitating cloud systems associated with the Meiyu frontal cyclone, special observational campaigns have been conducted in the downstream of the Yangtze River during June and July in the year 2001 (IOP-2001) and 2002 (IOP-2002). We deployed an L-band Wind Profiler (WP) with Radio Acoustic Sounding System (RASS) at the Meteorological Observatory, Dongshan within a mesoscale network which consists of three X-band Doppler radars, three AWS and Micro rain radar to observe the inner structure of precipitating cloud systems seen frequently in the observational area. WP 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. We made an attempt to understand the evolution of the turbulence structure of the convective boundary layer, with an emphasis on the nature of the decay of turbulence during morning and evening transition period during Meiyu period. A study was also carried out during intensive observational period (IOP-2001 and IOP-2002) to understand low-level-jet phenomena that plays a dominate role on the formation of Meiyu precipitating clouds. Zenith pointing WP provides high vertical resolution observations of the precipitating cloud systems that advect overhead. The precipitating cloud systems observed during IOP-2001 and IOP-2002 were divided into three rain [convection, mixed (convection-stratiform) and stratiform] types based on the reflectivity above melting layer and the differences of the falling speed of precipitation particles between 3 and 6 km altitude. In the passage of the cloud systems, during IOP-2001, convective and mixed types of rain systems are pre-dominant whereas during IOP-2001 convective systems embedded within a wide stratiform precipitation were observed. Differences between the cases in IOP-2001 and in IOP-2002 are mainly due to the difference in the distribution of water vapor and local environmental conditions. Our observational results suggest that large difference in relative humidity and horizontal wind speed apart from the large scale systems disturbances.
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