1961～2005年新疆夏季低云量长期变化特征及影响因素分析

利用新疆51个观测站1961～2005年低云云量资料,采用趋势分析、小波分析等方法分析了新疆夏季低云量的长期变化特征,并对500hPa环流指数与新疆夏季低云量做奇异值分解,重点讨论了极涡对新疆夏季低云量的影响。结果表明:近45年新疆夏季低云量增加趋势显著,并在1987年发生突变;新疆夏季低云量存在2～3年、准6年和准11年的显著周期;环流分析表明新疆夏季低云量与副热带高压、极涡及青藏高原高度场指数关系密切,当极涡面积减小、强度减弱时,西亚高空急流偏弱,新疆上空高空急流偏强,而低层大气主要表现为南风增强,水汽输送辐合加强,因此新疆夏季低云量偏多,反之,低云量偏少。

Analysis of Long-Term Variation Characteristics and Influence Factors of Summer Low Cloud Amount in Xinjiang during 1961-2005

Using the data of 51 weather stations during 45 years(1961-2005),the long-term temporal variation of summer low cloud over Xinjiang is analyzed by linear trend estimation and Morlet wavelet analysis.The relationship between 500-hPa circulation index and summer low cloud over Xinjiang is examined by means of singular value decomposition,and the impact of polar vortex on the summer low cloud in Xinjiang is discussed.The analysis shows that the summer low cloud in Xinjiang has remarkably increased in recent 45 years,and quasi-two-year,quasi-six-year,and quasi-11-year periodic oscillations were observed in summer low cloud amount.In addition,an abrupt change is found around 1987.The results indicate that the summer low cloud amount in Xinjiang is closely related to the summer subtropical high,polar vortex,and the Qinghai-Xizang Plateau height field index.With weak polar vortex,the upper-level westerly jet in West Asia weakens while the westerly jet in Xinjiang strengthens and correspondingly in lower atmosphere,the south wind increases in Xinjiang accompanied by stronger water vapor transport,which leads to increased low cloud over the area.