越赤道气流对副高脊线北抬至25°N的影响

Impacts of Cross-equatorial Flow on Subtropical High Ridge Jumping Northward to 25°N

副高脊线北抬至25°N的时间早晚是福建前汛期结束和开始进入夏季的重要环流背景。应用850hPa月平均风场、500hPa环流场和西太平洋副热带高压脊线北抬至25°N日期及福建省25个代表站(县)6—7月的降水为基本分析资料,首先标定副高北抬至25°N的标准与年例,其次采用合成分析法揭示异常年例6月850hPa风场的基本特征,进而探讨了索马里越赤道气流强度变化对副高北抬至25°N的影响关系,最后对2005年进行诊断。其主要结果有:(1)6月索马里越赤道气流强劲(不够明显),较常年偏强(偏弱),有利于副高北抬至25°N提早(推迟);(2)5—6月索马里越赤道气流强度与500hPa东亚至西太平洋中纬度区域的高度场呈现正相关关系,该区域高度场高(低)有(不)利于副高主体北抬,为副高北抬25°N时间提早(推迟)提供有利环流背景;(3)索马里越赤道气流强度为副高北抬至25°N提供了一个较强的预报预测信号;诊断2005年副高北抬至25°N提早,实况与诊断相符。

Using 850hPa mean monthly wind data, as well.as data of 500hPa height, date of the Western Pacific Subtropical High ridge jumping northward to 25°N and precipitation data from June to July at 25 representative weather stations in Fujian, the criteria for the anomalous date of the subtropical high jumping northward to 25°N are defined and the anomalous years are found, the general characteristics of 850hPa wind field in June of the anomalous years are analyzed with the composite analytical method, and the effects of intensity of the Somali cross-equatorial flow on the subtropical high northward jumping to 25°N are discussed. The results are as follows： The Somali cross-equatorial flow with above-normal （below-normal） intensity in June contributes to the subtropical high jumping northward to 25°N earlier （later）. The correlative coefficients between intensity of the Somali cross-equatorial flow from May to June and 500hPa heights in mid latitudes over the region from East Asia to the western Pacific are positive. The favorable circulation for the subtropical high northward jumping to 25°N earlier （later） is the higher （lower） heights in the region. Intensity of the Somali cross-equatorial flow could be a signal for predicting the time when the subtropical high jumps northward to 25°N. Based on the above results, the date of the subtropical high jumping northward to 25°N is diagnosed. It shows that the diagnosed result is correct.