ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Effect of Shape Parameter of Raindrop Spectrum on the Simulation of Meiyu Rainfall
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Abstract:
The raindrop spectrum shape parameter, which has significant spatiotemporal distribution features, is set as a constant in the Doublemoment Bulk Microphysics Scheme (DBMS) using Gamma distribution function. Based on Milbrandt 2mon (MY) DBMS, four Meiyu precipitation cases are simulated coupled with four empirical relationships between shape parameter (μr) and slope parameter of raindrops which are concluded from the observations of raindrop distribution. The analysis results suggest that μr has some influences on precipitation. Adopting the diagnostic formulas of μr is positively helpful for improving systematic biases of Meiyu rainfall and shows certain correction ability to the localization of rainfall distribution. The good response of heavy precipitation to μr reflects the clear tendency of improvement. Calculated by the empirical formula, μr increases generally. In the mid and lowertroposphere, μr decreases with the increase of rainfall intensity. The decline in raindrop water content and the increased raindrop massweighted average terminal velocity, which is directly related to μr, are the direct causes for the changes of precipitation. The difference in improving degree between the light and heavy rainfalls mainly results from the different response features of their variable fields. The varying trend of warmcloud particle features of severe rainfalls is consistent with that of light rainfalls, but there are considerable differences in their varying degrees. While it rains lightly, the response characteristics of physical fields to μr present similar varying trends and some linear features. However, in the case of heavy precipitation, the cloud microphysical process and ambient condition experience complex interactions with each other and no significant laws can be followed.
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