| Two cases of spring stratus precipitation processes occurred during March 30 to April 2, 2003 and April 4 to 5, 2002 have been analyzed in this paper. The macro characteristics of status cloud systems have been studied by using every 3-hour sounding data, satellite cloud pictures, radar echoes, synoptic charts, surface rainfall, raindrop size distribution and microwave radiometer. The spatial distribution of precipitation particles and the mechanisms of their formation were studied by one-dimension stratus model. Thus, spring stratus precipitation conceptual model was primarily established in Henan Province.Analyzed results of macro observed data showed that the configurations of stratus cloud systems were inhomogeneous, and stratus cloud systems consisted of several single clouds. Different clouds were departed by obvious borderline, and the height of cloud top changed between 4 and 8km. The height of 0℃ level occurred at about 3.5km height which was meant that super-cold cloud existed. The temperature of potential instability area was about 0℃ in the warm area and between -10℃ and 0℃ in the cold area. Maximum vapor content existed at 700hPa level, and the vapor came from south or ease-south below 700hPa level and from west-south above 700hPa level. Positive vertical velocity existed between 700hPa and 500hPa. There were wind shear and maximum wind speed occurred above or below the height of potential instability area and one of them happened before potential instability. Heavy rainfall occurred in the warm area, and maximum rainfall lay in the windward slope where the width of raindrop size distribution was broadened and sometimes it was bimodal spectrum. The shape of rain band in cold area was zonal, and the area of rain band was small. The width of raindrop size distribution in the warm area was narrow and its shape was single model.Simulating results of one-dimension stratus model showed that the content of cloud water that grew up by deposition process was the largest in the warm area, andcloud water existed between 2km and 6km. In the warm area, the formation of rain water which existed between 1km and 4km was behind of the formation of cloud water, and the development of rainwater was depend on collecting cloud water. The occurrence of graupel that grew up by the means of collecting cloud water was behind of rain formation, and existed in the lower layer of cloud water. In the cold area, ice phase particles were the main particles in the cloud. Ice crystals were formed by means of deposition process and existed at the top position from 6 to 8km. Snow content was highest in the cloud and existed between 2 and 6km. Snow grew up by deposition primarily and by collecting super cold cloud water secondly. Graupel that grew up primarily by collecting ice crystal existed between 1 and 3km. Collecting cloud water and snow auto conversion were the mainly ways of graupel development.Through synthetic analysis of stratus cloud systems, stratus precipitation concept model has been primarily established. It was well known that the main process of precipitation formation was collecting cloud water in the warm area and ice phase particles melting in the cold area. Positive vertical velocity existed between 700hPa and 500hPa in the warm area and near surface in the cold area. Wind convergence existed at the height of 700hPa, and divergence existed above and below the height of 700hPa. Maximum vapoT content intensified at 700hPa level. Vapor came from south or east-south in the warm area and from south-west in the cold area. Potential instability existed near 0℃ in the warm area and between -10℃ and 0℃ in the cold area. The occurrence of potential instability was corresponding with maximum rainfall and maximum vapor content. |
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