Abstract: Using the ground meteorological observations and meteorological sounding data during November to March from 1999 to 2014 in Anqing station,this paper analyzed the temporal-spatial distribution characteristics of different precipitation phases and the performance and transform of weather systems affecting conversion process between rain and snow.The relationships of different precipitation phases with temperature and thickness stratification were investigated under three weather phenomena,i.e.,conversion between rain and snow,snow,and ice rain or ice particles.The results reveal that solid precipitation in Anqing city mostly appears from November to March.The phase transform is better identified when considering the temperature at 850 hPa and between 850 hPa and ground.The precipitation is liquid when the temperatures at 850 hPa,925 hPa,1000 hPa,and surface are larger than or equal to -4℃,-4℃,-1℃,and 1℃ respectively.The further decrease in temperature below 850 hPa level results in the transforming from rain to snow.Except for the above temperature conditions for transforming from rain to snow,direct snow will happen when the temperature at 850 hPa decreases to -6℃.For the transforming between rain and snow,the critical values of thicknesses for 850-700 hPa and 1000-850 hPa are 154 dagpm and 129 dagpm,respectively.When they are less than critical values,it is snow;when they are larger than critical values,it is rain.The atmospheric level at 0℃ (L0) can be regarded as one of an index for the phase conversion of precipitation.The transforming from rain to snow will happen when L0 is approximately equal to 1000 hPa.The inversion temperature phenomenon generally appears during the precipitation period.When a warm layer above 0℃ exists between 850-700 hPa,it is ice rain or ice particle.While the temperature at inversion temperature layer is less than 0℃,it is snow.

Key words: Precipitation phase, Rain and snow conversion, Influencing system, Thickness stratification, Inversion temperature, Criterion test