Abstract:

Based on the conventional observation, NCEP reanalysis data and values of TBB and OLR of FY-2E, the comprehensive diagnostic analysis of a wide range and heavy snow, rain and freezing weather process from 24 to 25 April 2014 in eastern Yellow River of Gansu Province was done. The results show that the cold air on 500 hPa in front of the Ural mountains blocking high ridge accumulated and caused the collapse of blocking ridge, which made the transverse trough in eastern Ural Mountains to turn vertical trough and move southward, then guided a massive cold air to southward, therefore all of the above provided a large-scale circulation background for the heavy rain and snow weather process. The influence systems of the cold trough and mesoscale shear line on 700 hPa, ground cold front and cold high directly triggered the heavy snow and rain weather. The relative humidity above 90% on 700 hPa, high humidity column, strong moisture transport channels and persistent moisture convergence at low-level were the important water vapor condition to cause the weather process. The suddenly strong declining temperature before the snowfall in northern of Yellow River of Gansu provided the rain and snow conversion and mositure condensation conditions for the weather process. Simultaneously, the intersection and confrontation of the cold and warm air and temperature inversion in frontal zone provided the important thermal mechanism, and the strong upward motions and its sustaining and strengthening provided the powerful dynamic mechanism. The thermal instability parameters and distribution of temperature advection at upper and low levels reflected the atmospheric instability to some extent. The distribution of TBB and highest height of negative vertical velocity reflected the convection features of the weather process, and the evolutions of OLR and TBB were good predictor for the weather process.

Key words:  rain, snow and freezing injury, influence system, physical diagnosis, TBB, OLR

摘要：

利用常规观测资料、NCEP再分析资料及FY-2E卫星云图，对2014年4月24～25日甘肃河东地区一次大范围雨雪冰冻天气过程作综合诊断分析。结果表明：500 hPa乌拉尔山脊前冷空气积聚造成的阻塞脊崩溃，促使其东部横槽转竖南压，引导冷空气大举南下，为此次强雨雪天气提供了大尺度环流背景；700 hPa冷槽和中尺度切变线、地面冷锋、地面冷高压，是引发此次大范围强雨雪天气的直接影响系统。700 hPa上90%以上的相对湿度、强水汽输送通道和低层持续的水汽辐合，是形成此次强雨雪天气的重要水汽条件；降雪前河东北部地区的骤烈降温为此过程提供了雨雪转换和水汽凝结条件；冷暖空气交汇与对峙、锋区逆温为此次强雨雪天气过程提供了重要热力机制；强烈的上升运动及其维持与增强，为此次天气过程提供了有力的动力机制。热力不稳定参数及温度平流的高低空分布一定程度上反映出暴雪区上空层结的不稳定性；云顶亮温（TBB）的分布及负垂直速度所达的高度均反映出此次过程的对流性特征；OLR和TBB的演变对此次降水有很好的指示意义。

关键词: 雨雪冻害, 影响系统, 物理量诊断, 云顶亮温, OLR