Case Study Of Precipitation Processes Based On Doppler Radar Data

Characteristics of two precipitation cases have been analyzed based on Doppler radar echo intensity, radial velocity, and spectrum width, sounding and surface rainfall intensity observation. The cases occurred on July 5, 2004 in Jilin and on September 7 and 8, 2006 in Guizhou, the former is a large scale strtiform precipitation process, and the later is a mixed one. The results addressed that:1) For large area stratiform precipitation, according to the changes of cold and warm advection and changes of convergence and divergence with altitude retrieved from radar images, the wind field structure of this precipitation can be analyzed, and the occurrence of rainfall can be deduced. And distribution of spectrum width also indicates this is a stable precipitation. While for the large area precipitation ease of mixed clouds, it has typical echo feature of mixed clouds precipitation. The change of radial velocity field's distribution from micro-scale motion to large-scale can well deduce the evolvement of mixed clouds precipitation. And the distribution of spectrum width also well indicates this is a precipitation of mixed clouds.2) Utilizing multi-elevation and self-adjust VAD method respectively, wind field structures are calculated quantitatively of large area stratiform precipitation and that of mixed clouds. And the outcome of quantitative calculation and that of sounding and qualitative analysis are compared. The result shows that the wind field structures derived from three ways are accordant in general. So wind field structure from qualitative analysis is reliable and credible, and can be used to deduce the occurrence of rainfall and to predict large area precipitation.3) That case in Jilin is analyzed in the term of typhoon's spiral rain band. And some important observation facts are got from the evolvement of radar images, which conform to the wind field features of typhoon's spiral rain band. Two different scale systems interact and whole rain band circumvolve and move towards the west. Wind direction changes and speed is increased in middle and high level, velocity centers in low and middle level are distributed asymmetrically, and the speed of some weak echoes in middle and high level is very high.