Abstract:Based on upper air sounding and surface observations in winter of 2001-2010, the formation physical process of freezing rain and ice pellet at different regions are investigated. It is found that: (1) Except northern China region, the formation mechanism of freezing rain in China is mostly due to a warm rain process. In northern China region, freezing rain with melting process only accounts for 39%, but the higher latitudes, the higher ratio of melting process freezing rain. Warm layer aloft is an important characteristic of freezing rain weather. And its main functions are water vapor supply and frontal system maintaining, thus help to produce precipitation. Negative temperatures at low levels and surface could be the upmost factor for freezing rain. (2) Melting process is the main formation mechanism of ice pellet in China. Generally, cloud top of ice pellet is higher than that of freezing rain. Warm layer’s thickness and intensity of ice pellet are weaker than those of freezing rain. That is because weaker warm layer only partly makes ice crystal and snow aloft melt, thus ensure their refreezing within low levels. Wind speed at 700 hPa of ice pellet is commonly smaller than that of freezing rain, which, on the one hand, reflects the lower requirement of water vapor supply for ice pellet, and weaker warm layer aloft on the other hand. Cloud top, warm layer thickness and intensity, low level dew point depression, wind speed at 700 hPa and surface temperature are good factors to discriminate freezing rain from ice pellet, but in different regions, the effectiveness of these factors is different. The main difference of freezing rain and ice pellet in Southwest China is the surface temperature, and other factors play a secondary role due to unobvious difference of them.