北京降水相态判别指标及检验

为提高降水相态预报准确率，以北京南郊观象台为代表站，选取1951年1月至2011年4月逐日20时至20时出现的雨夹雪日数，统计分析其月变化特征；再选取2000-2011年10月-4月08时和20时出现的雨、雨夹雪、雪个例，使用与降水个例对应时次的地面及高空常规观测数据，统计分析各层常用气象要素在各降水相态判别中的作用，并找出主要影响因子及降水相态判别指标；应用多元回归方法，建立降水相态统计预报方程，并对方程及判别指标进行检验。结果表明：雨和雪的温度、露点平均值在低层（地面到850 hPa）有明显差异，但随着高度增加其差异逐渐减小；因雨和雪的温度露点差平均值各层差异均很小，使用温度露点差很难区分降水相态；经过对2011年11月至2012年3月出现的降水相态进行检验可知，总结出的地面温度和露点判别指标以及降水相态统计预报方程均有一定的参考价值，可为今后做降水相态预报服务提供参考依据。

Discrimination index of precipitation phase state and its verification in Beijing

To improve forecast accuracy of precipitation phase state,the variation of sleet day was analyzed based on the daily meteorological data from 20：00 to 20：00 during January of 1951 to April of 2011 from the southern suburb observatory station of Beijing as a representative station.The cases of rain,sleet,snow were selected at 08：00 and 20：00 from October to April during 2000 to 2011,and the effects of conventionally meteorological elements in each layer on precipitation phase state were analyzed according to their corresponding ground and upper meteorological data,and the main influencing factors and the discrimination index of precipitation phase state were found out.A forecast equation of precipitation phase state was established by a multiple regression method.The equation and the corresponding discrimination index were tested.The results indicate that the averaged temperature,dew-point values from rain and snow at lower layer （from the ground to 850 hPa） differ significantly.Both differences decrease with the increase of height.The mean dew-point difference of temperature in each layer is not significant and hardly to use for distinguishing the precipitation phase state.By the test of precipitation phase state from November of 2011 to March of 2012,it shows that the discrimination index and the forecast equation could provide references for forecast of precipitation phase state.