ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Analysis on the Mechanism of the 17 March 2012 Precipitation Type Variety in Beijing
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Abstract:
Due to the limitation of data resolution, the understanding of mechanism for precipitation type transition is not deep enough. During the night of March 17, 2012 in Beijing， the precipitation types had gone through three stages of the rain, sleet and snow. By using sounding data, microwave radiometer data and the retrieval results from Doppler radar and mesoscale model, the temperature profiles in 3 precipita tion stages are analyzed and then the mechanism leading to temperature differences is discussed also. The results show that, in snow stage, the depth of ice layer (including snow, ice and supercooled water mixing) becomes thicker and its base is closer to the surface. The main difference of temperature profile for three precipitation stages exists in the lower troposphere, especially around the lifting condensation level. The height of 0℃ level relative to the cloud base is closely related with the precipitation phase. In the rain stage, the 0℃ level is higher than the cloud base; but for the sleet, the 0℃ level goes down below the cloud base when the snow is observed. The cold air causes such difference. However, the way is different. When the rain turns to sleet, the cold air is transported to Beijing by easterly wind. As the result, the boundary layer becomes cooler. However, in sleet to snow stage, the temperature in the lower troposphere reduces further mainly due to the cold air invasion accompanied with a trough passing by. Therefore, the mechanism of precipitation type variety is complicated in Beijing.
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