福建入夏早晚异常的风场特征分析

本文以850 hPa、200 hPa月平均风场和西太平洋副热带高压脊线北抬至25°N日期资料及福建省25个代表站(县)5—7月的降水资料为基本分析素材。首先标定福建入夏异常的标准与年例,其次揭示850 hPa2、00 hPa 6月风场与异常年例的基本特征,进而探讨了对福建入夏早晚的影响关系。结果表明:在低层索马里-阿拉伯海区的越赤道气流强劲,南海至东亚低纬区域西南风偏大,西太平洋区域低纬度地区南风减弱、东风强劲,且东西风交汇区偏西;而在高层辐合区东风范围偏大,索马里-阿拉伯海区的区域东风风速强劲,青藏高原南侧和副高主体季节性位移的关键区以吹东风为主,东亚区域经向度小,位于青藏高原至我国东部区域范围内,形成一逆时针“距平”风环流;在此高低层风场特征的匹配下,有利于福建提早进入夏季;反之亦然。

AN ANALYSIS OF THE WIND FIELD FEATURES RELATED TO THE ANOMALOUS BEGINNING TIME OF SUMMER IN FUJIAN

Based on 850 hPa and 200 hPa monthly mean wind,the date of the subtropical high ridge moving northward to 25 N and the precipitation observed from May to July by 25 representative weather stations in Fujian,the criteria of the anomalous beginning time of summer in Fujian were defined,the general characteristics of 850 hPa and 200 hPa wind fields in June of the abnormal years and their relation to the beginning time of summer in Fujian were analyzed and discussed.The results are as follows:In the year when the beginning of summer in Fujian is abnormally early(late),in the lower troposphere,the cross-equatorial flow over Somalia and Arabian Sea is stronger(weaker) than the normal,the southwesterly wind in the region from the South China Sea to the low latitudes of East Asia is larger(smaller),and in the low latitudes of the West Pacific,the southerly wind decreases(increases) while the easterly wind is stronger(weaker),and the easterly and westerly wind meets in the west(east) to their normal convergence region;in the upper troposphere,the easterly(westerly) wind bound in the convergence area enlarges(shrinks),the easterly(westerly) wind prevails on the south side of the Qinghai-Xizang Plateau and over the key area for the seasonal shift of the subtropical high,the easterly wind strengthens(weaken) over Somalia-Arabian Sea region,the circulation meridionality is large(small) over East Asia,and the southerly wind over the Qinghai-Xizang Plateau and the northerly wind in East China decreases(increases),that forms an anticlockwise(clockwise) circulation of wind anomaly over the region from the Qinghai-Xizang Plateau to East China.Such collocation of wind fields in the lower and upper levels helps the main body of the subtropical high move northward to 25 N earlier(later).As a result,the rainfall in June over Fujian tends to be less(more) than the normal and summer comes ahead(delays).