滇西北春夏连旱的环流特征分析

Analysis of Circulation Characteristics of Spring-Summer Droughts over Northwestern Yunnan Province

通过对1971～2000年云南丽江区域平均5月雨量与北半球100hPa及500hPa高度场的相关分析，得出影响丽江区域平均5月雨量的主要影响系统为100hPa南亚高压、500hPa南海副高、孟加拉湾低值系统及中高纬度地区的新疆高压（脊），这4个关键因素的异常及强弱影响丽江5月雨量的多寡。通过对2005年5月100hPa及500hPa的实况场与距平场的对比分析，得出造成2005年严重春夏连旱的环流成因为南海副高偏强、盂加拉湾低值系统偏弱、南亚高压及新疆高脊偏弱，造成西南季风云团及冷空气难以在云南上空交汇而导致严重的干旱。

The correlation analysis is made between the May mean rainfall over Lijiang from 1971 to 2000 and the height fields of 100 hPa and 500 hPa during the same time. It is found out that the main influencing weather systems influencing rainfall in May in Lijiang include the 100 hPa South Asia high, 500 hPa South Sea subtropical high, low system over the Bay of Bengal, and Xinjiang high （ridge） at mid-high latitudes. Through abalysing the observed and anomaly fields in May 2005 at 100 hPa and 500 hPa, it is shown that the circulationpattern causes of the drought persisting from spring to summer in May 2005 include the strong the subtropical high over the South Sea, the weak low over the Bay of Bengal, and the weak-than-normal South Asia high and Xinjiang high, which together obstructed the confluence of the Southwest Monsoon cloud cluster and the cold air from noth over Yunnan, so to result in the severe drought.