秋季高原切变线的统计特征及环流形势分析

Statistical Characteristics and Circulation Situation of Shear Line in Autumn Tibet Plateau

摘要: 高原切变线是青藏高原地区强降水和暴雪天气的主要影响系统。本文利用0.5˚ × 0.5˚格点的CFSR (Climate Forecast System Reanalysis)再分析资料，对1979~2010年秋季(9~11月) 500 hPa高原切变线的空间分布、时间分布和移出次数等特征进行了统计分析，并根据横、竖切变线的天气个例，对比讨论了不同切变线的基本环流形势特征。分析结果如下：统计时段内，秋季高原切变线共出现146次，其中横切变线130次，且多初生于高原中西部，竖切变线16次，多初生于高原中东部。分析高原切变线的时间分布，发现秋季9月生成次数最多，11月最少，且主要生成在北京时间23时至次日02时之间的前半夜。对秋季高原切变线的持续时间进行分析，发现其持续时间主要集中在12小时以内。移出高原的切变线很少，占总次数的10.96%，其中，大部分竖切变线会移出高原。通过对两类切变线天气个例的500 hPa环流形势进行对比分析，发现500 hPa西太平洋副高外围西伸至高原，高原北部出现负涡度中心时，易生成横切变线，横切变线与涡度零线平行，两侧南湿北干。与横切变线对比，西太平洋副高及其外围呈稳定的经向高压坝时易出现竖切变线，竖切变线水平涡度梯度明显，湿度梯度较弱。

Abstract: Plateau shear line is the main influence system of heavy rainfall and blizzard weather in Qing-hai-Tibet Plateau. Using the CFSR reanalysis data in 0.5˚ × 0.5˚ grid statistically analyzed the shear lines spatial distribution, time distribution and the number of removal times in autumn (September-November )of 1979~2010. And the basic circulation situation of different shear lines is discussed and compared. The results are as follows: in autumn, there are 146 times of shear lines appearing in the plateau with 130 times of transverse shear line and 16 times of vertical shear line. In the meanwhile, most vertical shear lines are found in the middle and eastern part of the plateau; transverse shear lines mainly distribute in middle and western plateau. The autumn plateau shear lines are mainly produced from 23 PM to the 02AM (Beijing time). The number of shear lines removal from the plateau is very small, accounting for 10.96% in the total amount. Through the comparative analysis of the 500 hPa circulation situation of two types of shear line, we found that the partial easterly winds in the northern part of the plateau and the southward airflow from the Bay of Bengal meet on the plateau and form the main circulation situation of the transversal line. The periphery of 500 hPa subtropical high and the westerly belt overlapped with high pressure ridge conducive to vertical shear line.