2008年初中国南方持续性冰冻雨雪灾害形成的温度场结构分析

2008年初，中国南方发生了大范围、持续性低温冰冻雨雪天气，冻雨、暴雪灾害历史罕见，许多地方打破50年记录。文中主要从3种降水类型，特别是冻雨的地域分布和促使其形成的温度场层结及地面温度分布特征方面讨论了1月25日到2月2日冰冻雨雪灾害最为严重的过程阶段。分析表明，降雨、冻雨和降雪3种类型降水物的自南向北分布特征是由对流层中低层向北后倾的锋区在南北不同区域上的层结特征和地面温度条件决定的；在倾斜锋区存在背景下，在对流层中低层形成了产生冻雨的大气逆温特征和较低的地面（表）温度条件。逆温区大于0 ℃的暖层应具有合适的强度、厚度和高度，既不能太厚太低，也不能太薄太高。如果太厚太低，降水将会以雨的类型降落地面，如果太薄太高，降水则会以雪或冰粒子的类型出现。这次过程中0—6 ℃的暖层在650—850 hPa,其下为低于0 ℃的次冻层，在次冻层温度较低的情况下，即使地面（表）温度在0—1 ℃，也可能形成冻雨或冰冻灾害。此外，在没有适宜逆温区存在的条件下，较低的地面（表）温度也能使“冰包水”物质、过冷却水滴降落到地面或雪融化成水后迅速凝冻成冰，或使冰冻维持而至灾。

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.