中国西南地区东部秋季干旱的环流特征及其成因分析

利用1961--2010年NCEP／NCAR再分析资料和全国753站月平均降水资料，研究了我国西南地区东部秋季干旱的环流特征及其成因。结果表明，西南地区东部秋季降水存在明显的年际和年代际变化。其中，年代际变化主要表现为，在20世纪80年代中后期，降水存在由多转少的突变；降水量年际变化则与苏门答腊一西太平洋和热带东太平洋的海温分布存在很好的关系。当苏门答腊一西太平洋和东太平洋海温呈现“＋-”异常分布时，引起大气热源的异常，加强哈德莱环流，同时，在南海及孟加拉湾附近激发出异常气旋性环流，而西南地区东部则处于南海气旋性环流外围异常偏北气流控制，削弱了孟加拉湾的水汽输送，从而造成西南地区东部的干旱。通过大气环流模式NCARCAM3．0（Community Atmosphere Model3．0）的海温异常试验，验证了上述观测结论。

Atmospheric circulation characteristics and cause analysis for autumn drought in the eastern region of Southwest China

Based on NCEP/NCAR reanalysis data and rainfall data from 753 weather stations in China, the causes for droughts in the eastern region of the southwest part of China （ESWC） are discussed in this paper. The results indicate that both interdecadal and interannual changes are obvious in the precipi- tation in ESWC. The main characteristic of interdecadal change was that a sudden shift from wetness to dryness appeared around the late 1980s in ESWC;the interannual variations of precipitation are highly related to the SSTA over the regions from the eastern Indian Ocean（ around Sumatra） and western Pa- cific （EIWP） to eastern Pacific （EP）. By inducing abnormal atmospheric heating, the positive and nega- tive abnormal patterns in SST over the E1WP and EP induces cyclonic circulations around South China Sea and Bay of Bengal, together with enhanced Hardly Cell. In this case, the studied area is then con- trolled by both northerly wind and enhanced downward vertical motion while the water vapor transport from the Bay of Bengal is reduced. All the above reasons lead to droughts in the studied region. The a- bove observational results are further confirmed by a series of numerical model simulations using NCAR CAM3.0 （ Community Atmosphere Model 3.0 ）.