南亚高压对川渝地区盛夏极端旱涝的影响分析

THE ANALYSIS ON EFFECT OF SOUTH ASIA HIGH IN MID-SUMMER EXTREME DROUGHT AND FLOOD YEARS OF SICHUAN-CHONGQING REGIONS

利用NCEP/NCAR资料对川渝地区两个极端年1998年(涝年)和2006年(旱年)进行分析,结果表明,涝年南亚高压辐散强,脊线位置比多年平均偏南,西太平洋副热带高压(简称西太副高)主体西伸,脊线偏南;旱年南亚高压的辐散比涝年弱,脊线位置比多年平均偏北,西太副高脊线亦偏北。从动力特征来看,旱(涝)年,高层大气相对负(正)涡度平流的垂直分布有利于大气产生下沉(上升)运动,且南亚高压距平环流存在辐合(辐散),与之对应的低层存在辐散(辐合)特征;热力分析亦表明,旱(涝)年的中低层多为暖(冷)平流,具有负(正)非绝热加热特征,且非绝热加热的垂直分布特征,有利于南亚高压距平环流局部辐合(辐散)加强,并对中低层系统的垂直运动产生影响。因此,一定程度上川渝地区两个极端旱涝年的出现与其上空的垂直运动变化密切相关,是由南亚高压与中低层系统的相互配置引起的。

Using NCEP/NCAR data to analyze an extreme flood year（1998） and an extreme dry year（2006） in the Sichuan-Chongqing region, this work showed the following results. The positive divergence of South Asia High （SAH） was stronger in the flood year; and compared to annual average, the position of the ridge line of SAH was also southward; Western Pacific Subtropical High（WPSH） extended westward and its ridge line was southward. In the drought year, the positive divergence of SAH was weaker, its ridge line was northward, and the position of WPSH was also northward. As shown in the dynamics, in drought （flood） years, negative （positive） vorticity advection in the upper atmosphere could cause the atmosphere to ascend （sink）, and anomalous circulation of SAH displayed divergence （convergence）, and anomalous circulation of the lower atmosphere showed convergence （divergence）. Thermal structure of the atmosphere shows that there was warm （cold） temperature advection in the lower atmosphere, and the vertical distribution of diabatic heating caused SAH＇s local circulation to display convergence （divergence） and affected vertical motion of the lower atmosphere circulation eventually. To some extent, the two extreme years of the Sichuan-Chongqing region had good relation with the vertical motion of atmosphere circulation and the variation of such vertical motion was caused by differences of interactions between SAH and lower atmosphere circulations.