安庆市降水相态识别判据研究

Analysis of identification criterion of precipitation phase in Anqing city

利用1999—2014年11月至翌年3月安庆站逐日地面气象观测资料和探空资料,分析了安庆站不同降水相态的时空分布特征和雨雪转换过程中影响系统的配置及转变,选取雨雪转换、降雪和冰粒(包括冻雨)3种天气现象,研究不同降水相态与特性层温度及厚度层结的关系。结果表明:1999—2014年安庆市固态降水集中出现在11月至翌年3月;有降水相态转换的过程中,将850hPa及以下各层温度与地面温度结合对降水相态转变的识别具有更好的效果,当T_(850hPa)≥-4℃、T_(925hPa)≥-4℃、T_(1000hPa)≥-1℃、T_(地面温度)≥1℃时可以判定降水相态为降雨,各层温度继续降低将出现雨转雪,直接降雪在以上指标的基础上需要850hPa的温度降至-6℃及以下;H_(850—700hPa)和H_(1000—850hPa)厚度层结雨雪转换的临界值分别为154dagpm、129dagpm,低于此值则为雪,反之为雨;0℃层高度也可以作为降水相态转换的指标之一,当0℃层高度下降至1000hPa左右时为雨转雪;降水过程中逆温层普遍存在,各种降水类型的区别在于冰粒(冻雨)在850—700hPa之间存在一个0℃以上的暖层,而降雪需要逆温层温度小于0℃。

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 above0 ℃ 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.