A study of the structure and microphysical processes of a precipitating stratiform cloud in Jilin

Based on airborne cloud particle probe observations, Doppler radar measurements and surface precipitation data, the macroand microstructure as well as precipitation mechanisms of one precipitating stratiform cloud occurring on 1 July 2004 in Jilin Province were studied comprehensively by using a onedimensional stratiform cloud model. With those quantitative results, we had a further insight into the Koo Chenchao's threelayer cloud conceptual model and also got some new conclusions referring to the seederfeeder processes. According to field observations, the nonuniform precipitation was produced by a typical stratiform cloud. The cloud structure could be explained well with the threelayer cloud model where the first layer is the ice crystal layer, including primarily small amounts of ice crystals. The mixedphase layer (the second layer), with altostratus and stratocumulus as the main cloud region, includes such processes as depositional growth, riming, aggregation and freezing of supercooled cloud water. And the remaining layer is the warm layer, in which obvious radar bright band was observed from Doppler radar. Based on the above observations, the numerical simulations of cloud structure and precipitation formation processes were conducted. The numerical results showed the presence of the three layer structure at the mature stage of cloud development. In the first layer (7.8－10.0 km), there was little ice and snow crystals which grew mainly by depositional growth. And in the second layer (3.8－7.8 km) the ice and snow crystals falling partly from the first layer grew through the Bergeron process initially and later grew predominantly by riming processes. After that, the grownup snow and graupel fell to the third layer. Therefore, the melting of snow and graupel combined with subsequent collection of cloud water was the main source of rain drop mass growth. Our results indicated that 50%-60% of rain drop mass growth was associated with melting of ice particles falling from the second layer.  In summary, the seederfeeder processes existed between not only the first and second layers, but also the second and the third layers. In terms of the contribution to the total surface precipitation, the first, second and third layers produced precipitation mass of about 0.2%－0.4%, around 75% and 25%, respectively. Besides, sensitivity tests also suggested that the decrease of ice crystals in the first layer could cause a decrease of snow concentration of about 40%－90% at the upper part of the second layer, which had relatively higher degree of influence at the initial stage of cloud development, and later became less important with decreasing height and time. And variations of ice crystal concentration could cause average precipitation rate changes of between 2% and 8%. Therefore, although the first layer produced precipitation mass of less than 1%, its important influence could not be ignored.