华北北部相似形势下的两次雨转暴雪过程对比

利用加密自动站资料、风廓线资料、NCEP／NCAR1°×1°再分析资料和常规观测等气象资料，对2009年10月31日至11月1日和2012年3月17～18日发生在华北北部的2场相似形势的典型雨转暴雪天气过程进行了对比分析。结果表明：2次雨转暴雪天气过程都发生在过渡季节，并伴随雨雪转换，850hPa有明显锋区，锋前有倒槽发展，雨转暴雪出现在850hPa湿正压位涡项负值区（MPV1〈0）、湿斜压位涡项正值区（MPV2〉0）、整层大气可降水量大值区和700hPa的锋生函数脊线的重叠区域。700hPa出现冷平流中心且高度降低，近地层偏东风的有组织增强，850hPa温度≤-4℃，地面温度≤1℃是雨转雪的一个重要特征。

Comparison of Two Rain to Heavy Snowstorm Weather Processes Under the Similar Weather Situation in Northern Part of North China

Based on automatic weather station data, the wind profile data, NCEP 1 ° x 1 ° reanalysis data and the conventional observa- tions, the two rain to heavy snowstorm weather processes under the similar weather situation which occurred in northern part of north China were diagnostically analyzed. The results shows that the snowstorm accompanied with rain in northern part of north China often occured in transition season, the strong frontal zone and inverted trough were the important source of steam for these snowfall weather processes, which occurred in the overlapping zone of negative MPV1, positive MPV2, the atmospheric precipitable water and front gen- esis function. Temperature advections derived from the wind profile data and the northeasterly wind jet correlated to the time of snow- storm＇ s occurrence, temperature of 850 hPa ≤ - 4 ℃, temperature of surface ≤ 1 ℃, which can be used as an indicator in forecasting rain to snowstorm weather.