陕西强沙尘暴、特强沙尘暴天气气候特征分析

 从陕西1954—2003年所有沙尘暴记录所对应的3次或4次定时能见度观测资料中挑出最小能见度小于500 m的作为强沙尘暴记录,小于200 m的作为特强沙尘暴记录。然后挑取在一次过程中有3个或3个以上气象站出现强沙尘暴的过程共41次作为强沙尘暴过程,有3个或3个以上气象站出现特强沙尘暴的过程共6次作为特强沙尘暴过程。分析结果表明,20世纪90年代是陕西强沙尘暴、特强沙尘暴过程最少的时期。陕西强沙尘暴过程主要发生在春季,冬季次之,其中春季4月最多, 冬季2月最多。除春季、冬季外,6、11月也有发生。根据41次强沙尘暴过程出现前一日08时500 hPa环流形势分析,将造成陕西强沙尘暴天气的环流形势及影响系统分为蒙古冷（横）槽型、脊前下滑槽型、短波槽东移型和西北气流型4类,其中蒙古冷（横）槽型是造成陕西强沙尘暴天气最多的一种形势,占总次数的44%。陕西6次特强沙尘暴过程的环流形势及影响系统全为蒙古冷（横）槽型。根据地面冷空气入侵陕西的路径分析,将造成陕西强沙尘暴天气的冷空气路径分为西路、西北路、北路三条。

Analysis of Climate Characteristics of Heavy and Severe Sandstorms in Shaanxi Province

In this paper the heavy sandstorms are that whose shortest visibility is less than 500 m, and the severe sandstorms less than 200 m. These data were picked out from all the sandstorm records from 1954 to 2003 in Shaanxi province, with each record regularly observed by 3 or 4 times. Consequently there were 41 heavy sandstorm processes and 6 severe sandstorm processes picked out, with each sandstorm process recorded by more 3 stations or more. The analysis results show that the least frequency period of heavy and severe sandstorm processes in Shaanxi province is 1990's. Heavy sandstorm processes in Shaanxi happened mainly in spring, and secondly in winter. Thereinto the April is the most frequently in spring and the February is the most one in winter. Besides spring and winter, they also happened in June and November. Based on the 500 hPa circulations at 08h the day before the 41 heavy sandstorm processes happened, the circulations and affecting systems causing heavy sandstorm processes in Shaanxi are divided into four types: cold (crossing) trough from Mongolia, downslide trough before ridge, eastward movement of short wave trough and northwest airflow. Cold (crossing) trough from Mongolia is the most important pattern that caused heavy sandstorm processes in Shaanxi, which accounted for 45%. The circulations and affecting systems causing the 6 severe sandstorm processes in Shaanxi are all cold (crossing) trough from Mongolia. According to path analysis upon the invading cold air on surface, the cold air paths causing heavy sand storm processes in Shaanxi are divided into the west, the northwest, and the north way.