2010年秋冬季西南地区严重干旱与南支槽关系分析

Relationship Analysis between South Branch Trough and Severe Drought of Southwest China during Autumm and Winter 2009/2010

利用1951～2009年西南地区24个站点逐月降水资料以及NCEP/NCAR再分析资料,分析了2009/2010年冬季我国西南地区严重干旱的演变特征,并使用SVD、小波分析和合成分析揭示了南支槽与我国西南地区冬季严重干旱的关系。结果表明:2009/2010年西南地区冬季严重干旱从秋季10月份云南省开始出现大范围干旱为征兆,11～2月逐步发展到西南三省,3月减弱。从秋季10月到次年2月的降水持续偏少,加重了此次旱情。2009/2010年冬季西南地区严重干旱的开始、发展和减弱与同期500hPa南支槽活动及整层水汽输送有着密切的关系。我国西南地区11～3月降水和前期11月南支槽指数在10～12年周期变化上存在显著的反相关系,前期11月南支槽区负距平,南支槽指数偏弱,南支槽加深,水汽输送充足,西南地区降水偏多;反之,前期11月南支槽区正距平,南支槽指数偏强,南支槽变浅,水汽条件不足,西南地区降水偏少。SVD分析表明,高度场第一模态同性相关场的关键区在青藏高原南侧孟加拉湾地区,反映了南支槽强弱变化信息,第一模态的这对空间分布型表明18～20°N,84～92°E范围11～3月500hPa高度场异常偏低时,同期我国西南地区降水偏多;高度场第二模态同性相关场的关键区在22°N以南区域,反映了西风强弱变化信息。第二模态的这对空间分布性表明70～110°E之间22°N以南区域11～3月500hPa高度场异常偏低时,同期我国西南地区降水偏少。11～3月关键区500hPa高度场与我国西南地区同期降水在时空场上都有着很好的同步关系,并且前期500hPa高度场是我国西南地区11～3月旱涝情况的一种预测信号。

By use of the monthly precipitation dataset of 160 stations in China from 1951-2010 and NCEP/NCAR reanalysis data,the evolution characteristics of severe drought in southwest China from October of 2009 to March of 2010 are studied.At the same time,the relationships between south branch trough and severe drought in southwest China during the winter are analyzed by using wavelet analysis,Singular Value Decomposition and composite analysis.The results show that the large area drought take place in Yunnan in October as a sigh of the beginning of severe drought in southwest China,from November to February it spreads all over the southeast China,and in March it relieves.The beginning,evolution and weaken of severe drought in southwest China from Oct.to Mar.is closely related with the geopotential height at 500 hPa and the vertically integrated water vapor flux of the same time.The precipitation in southwest China from Nov.to Mar.and south branch trough index in Nov.both have the significant time-scale change of the 10 to 12-year,and the phases of them are significant opposite.When the geopotential height of south branch trough area in Nov.is negative anomaly or south branch trough index is weaker than usual,the rainfall in southwest China is more and vice versa.SVD analysis shows that in the left homogeneous correlation field of the first mode the Bay of Bengal region（18°~20 °N,84°~92 °E） is significant key region,and it reflects the information of south branch trough changes.The distribution of the first mode indicates that when 500 hPa geopotential height is negative anomalies in significant key region from Nov.to Mar.,the precipitation in southwest China from Nov.to Mar.will be positive anomalies,while in the left homogeneous correlation field of the second mode the 5° ~22 °N,70°~110 °E region is significant key region,and it reflects the information of westerly changes on the north side of the Tibetan Plateau.The distribution of the second mode indicates that when 500 hPa geopotential height is negative anomalies in significant key region from Nov.to Mar.,the precipitation in southwest China from Nov.to Mar.will be negative anomalies.The previous 500 hPa geopotential height is a forecast signal for the anomalies of precipitation of the same time.