南方两次降雪过程的降水相态模拟研究

Simulation Study on Precipitation Phase State in Two Snowfall Processes of South China

利用常规地面观测资料、NCEP GFS分析资料、卫星及多普勒雷达资料和中尺度数值模式WRF,通过对比分析寒潮型暴雪和冷暖空气对峙型(下称对峙型)雨雪两类天气过程的大气环流形势、温湿廓线和对流层中低层风场特征,发现温度平流的强度和高度层次是两类雨雪天气过程的最大差异。东部沿海地区的低层风向可以用来判定冷空气的强度和爆发时间。从热量的收支来看,温度垂直廓线的主要影响因子是温度的水平平流和非绝热过程。逆温层的出现主要是温度水平平流项的贡献;强降水期间,非绝热加热与温度水平平流的增温效果相当。对峙型降雪的平流降温明显小于寒潮型降雪,对峙型降雪的中低层更多的是暖平流。950hPa混合降水凝结比可作为降水相态的预报因子,混合降水凝结比接近100%,雪混合比>0.2g.kg-1,地面降雪;凝结比在95%～100%之间为降水类型过渡区,结合非绝热降温幅度和地面温度,可以用来判定过渡区的降水类型;凝结比<90%,地面温度在0℃以上,类型为降雨。

Atmospheric circulation, temperature and humidity profiles, and middle-low level wind field characteristics in weather processes of cold wave blizzard and the cold and warm air confrontational snow types were comparative analyzed. Results show that the maximum difference in the two processes is the in- tensity and height level of the temperature advection. The intensity and outbreak time of the strong cold air can be judged by the low-level wind direction in the eastern coast of China. In view of heat budget, the main impact factors for vertical profiles of temperature are horizontal advection of temperature and non-adi- abatic process. The emergence of temperature inversion layer is main attributed to horizontal advection of temperature. Non-adiabatic heating with the increasing of horizontal temperature advection is equivalent during the severe pricipitation period. Advection cooling in cold and warm air confrontational snowfall is significantly smaller than of cold-wave snowfall, there is more warm advection in the lower level of con- frontational type snow. The mixed precipitation condensation ratio on 950 hPa can be used for a predictor of precipitation phase state. When the mixed precipitation condensation ratio is close to 100% and snow mixing ratio is above 0.2 g · kg-1 , the precipitation type is snow. Condensation ratio between 95% and 100% is the transition region of precipitation type, combined with non-adiabatic temperature cooling am- plitude and ground temperature, which can be determined as ground precipitation types in the transition re- gion. If the condensation ratio is below 90% and surface temperature is above 0 ℃, the precipitation type is rain.