1960-2009年中国西北地区东部低层风切变对雨日的控制作用及其在不同季节的降水效率

利用中国西北地区东部61个气象站1960-2009年逐日降水资料,结合同时次NCEP全球再分析风场资料,在气旋性风切变辨识算法的支撑下,分析了近50年西北地区东部低层气旋性风切变演变对同期雨日多寡的控制与指示作用,结合低层水汽条件与气旋性风切变的配置关系,对其在不同季节对雨日的可能影响程度及降水效率进行了逐一比对与成因探讨。结果表明:在冷暖空气交汇频繁的春、秋两季,即一年中气旋性风切变多发时段,700 hPa气旋性风切变在干旱区和半干旱区,对雨日产生的差异性最为显著,降水效率相差达24%,而冬季仅为10%;通过对比分析西北地区东部不同季节风切变效率多年和少年比湿分布,发现在在春、夏两季,水汽条件对700 hPa气旋性风切变的降水效率影响最为显著。气旋性风切变降水效率概念的引入,不仅较为符合西北地区的天气气候特点,且能够较好地反映雨日与700 hPa气旋性风切变之间在不同季节与不同区域中的相关性,对现实预报有较重要的指示意义。

Control Action of Low-level Wind Shear to Rain Days and Its Precipitation Efficiency in Different Seasons over East of Northwest China during 1960-2009

In this paper, the observed data from 1960 to 2009 from 61 meteorological stations and the global reanalysis wind data are used to analyze the control action of low-level wind shear to rain days over the east region of Northwest China using the cyclonic wind shear identification algorithm method. Combined the analysis of configuration relationship between moisture conditions and cyclonic wind shear, influence degree of low-level wind shear to the rain days and precipitation efficiency are discussed in different seasons. In spring and autumn in which there are many cyclonic wind shear, the control action of cyclonic wind shear at700 hPa to rain days is the most significant between the arid and half arid areas. In spring and autumn, the precipitation efficiency is 24%, and in winter it is only 10%. The comparison of the humidity distribution between years with more wind shear efficiency and less wind shear efficiency shows that in the spring and summer, water vapor is the key determinants of precipitation efficiency of wind shear at 700 hPa.The introduction of the concept of cyclonic wind shear precipitation efficiency, not only has certain rationality, but also can reflect better the correlation between the rain days and cyclonic wind shear at 700 hPa in different seasons and different areas. Cyclonic wind shear precipitation efficiency has the important instruction meaning to weather forecast.