| Studies show that cumulus embedded stratus, an efficient precipitation cloud system, has a quite typically microphysical and thermodynamic structure which is different from either usual cumulus or stratus, and has not only a mixing of forms of cumulus and stratus but also a mixing of processes of cold-cloud precipitation and warm-cloud precipitation. Therefore, the studying of the natural mechanism of this type of precipitation is very meaningful not only to enhance the forecasting level but also to guide weather modification of such type of precipitation.The precipitation of cumulus embedded stratus on April18th-19th2009in Zhang Jiakou is simulated using a new generation of meso-scale numerical model WRF-ARW (V3.2) and comparatively analyzed from different scales with observation data. Based on comparison and analysis of different scales are the links between the further analysis. Get the following main results:(1) It is showed through comparatively analysis that the simulation of this precipitation process by WRF well. And from the simulations of weather situation, the distribution of cumulus embedded statistic cloud band and precipitation and radar echo, there is no temporal lag and the location is very accurate compared to the actual happening which means WRF has a very high ability of simulating. What’s more, through the comparison of microphysical features, it is found that the model behaves well in term of microphysics.(2) Results show that the west wind trough and the low from Mongolian area on700hPa. and the low vortex on850hPa are the main influential weather systems. The warm wet air from the southern and the low vortex from northwest Inner Mongolia, which converge in Zhang Jiakou region and thus are conducive to precipitation, are the main vapor suppliers. The cloud systems distribute in a northeast-southwest band which is1000km long and300km wide, and have lots of centers of cloud water, which are about tens of kilometers. The precipitation band is northeast-southwest too, and has number of rain cores. The hydrometeor in the cloud system is heterogeneous generally, and has the echo characteristics of typical cumulus embedded stratus as columnar echo of cumulus cloud embedded in uniform echo layer. Cumulus has the echo of columned with peak of50dBz and the horizontal scale of10-20km. From the cross-sectional map of cumulus echo, the cloud water content is heterogeneous either horizontally or vertically. The centers of precipitation are corresponding with the centers of graupel and snow in the upper layer,10-20km in horizontal. The locations of the above three are in accord with cumulus in the cross-sectional map of radar echo, which means that graupel, snow and rain are the main precipitation particles and the principle factor of radar echo.(3) The links between different scales of process in this precipitation are analyzed using model results and measurement data. Results show that large scale weather situation has great relationship with wind field, whose distribution determines directly the transport of vapor. The water vapor transported converges in the precipitation area, and is sent from lower to upper layer by low pressure and vortex, and vertical wind velocity, which is the necessary condition of cloud forming and developing, and thus is the links large scale weather situation and meso-scale cloud field. In this paper, the link between meso-scale and micro-scale systems is found by the analysis of cloud from macro and micro aspects. |
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