Analysis of temperature structure for persistent disasterous freezing rain and snow over southern China in early 2008.

Early 2008, a largescale and persistent low-temperature, freezing rain and snow weather occurred in southern China. The disaster caused by freezing rain and snow storm was unprecedented, and broke the 50 years record in many areas. In this paper, we mainly discussed the geographical distribution characteristics of the three different types of precipitation, especially freezing rain, and reasons from temperature stratification status and horizontal distribution of surface and ground temperature. Analysis showed that the distributive characteristics of rain, freezing rain and snow from south to north was determined by different stratification status in different regions of northward inclined cold front zone in the mid-low troposphere and surface temperature conditions. Under above front conditions, there must also be a specific vertical temperature structure in the mid-lower troposphere, i.e. the existence of obvious inversion layer and lower surface or ground temperature conditions. The inversion layer exceeding 0 ℃ should possess suitable strength, thickness and height, it should be neither too thick and low nor thin and high. The type of precipitation will be rain if the inversion layer is too thick and low, and it will be snow or ice vice versa. It seemed that a subfreezing layer below 0 ℃ existed beneath the warm layer of 0-6 ℃ between 650 and 850 hPa. And under colder conditions in the subfreezing layer, freezing might occur even if the surface temperature was between 0-1 ℃. Besides, if there is no suitable inversion layer for freezing rain, the ice-covered water drop, supercooled water or melted snow will freeze rapidly under conditions of lower surface and ground temperatures.