Doppler Radar Detection of Heavy Snow Distributed in South of Northeast China

Based on data from the China new-generation weather radar (CINRAD), a comprehensive study is performed of three heavy snow processes in the south of Northeast China during 2004-2007. Results show that the heavy snow in the south of Northeast China (HSSNC) is characterized as follows: 1) the area of echo over 18 dBZ is larger than 5×103km2in the CINRAD base reflectivity product and hourly snowfall is positively correlated with the snow echo; 2) there is large gradient of echo intensity at the boundary between rainfall and snowfall; 3) the echo intensity of the study snow is usually less than 30 dBZ, and the snow is mainly made up of liquid precipitation particles or melting solid precipitation particles when the intensity is larger than 40 dBZ; 4) the precipitation features and rain-snow boundary can be distinguished according to the echo intensity and its gradient, and the radiosonde and surface temperature records, which is meaningful to the forecast. At the beginning of heavy snowfall process, the zero line is clear with a structure like "S", which is the structure of warm advection wind. At the mature stage, the recombination wind field which is superposition of warm advection and large scale convergence predicts that the echo would be strongest. For the products of wind profile, the low-level water vapour transport has a direct intuitive significance for the change of precipitation intensity. During the heavy snow processes, the height of the echo top (ET) is low, slightly changing and relatively even, with its area a little smaller than that of the base intensity product. Meanwhile, products of the vertically integrated liquid (VIL) underestimate evidently the snowfall, and its area is much smaller than area of base reflectivity. Doppler radar detection and estimation of the hourly snowfall by optimization method on the extremely heavy snow on March 4th, 2007 has the similar trend with the observation, showing that the samples 50-100 km away from the radar are most in accord with the observation, and that up to 72% of the samples within a distance of 100 km from the radar overvalue the snowfall, which should be noted and revised in operational application.