1990年以来重庆秋季年代际干旱及其可能成因

Interdecadal autumn drought in Chongqing and its possible cause since 1990

采用1961—2012年重庆地区30站降水和气温资料、NCEP/NCAR全球大气再分析资料、NOAA海表温度资料等,基于由降水和气温计算得到的标准化降水蒸散指数(Standardized Precipitation Evapotranspiration Index,SPEI),对重庆地区秋季干旱的年代际变化特征及其可能原因进行了研究。观测结果表明,重庆秋季SPEI的变化特征主要表现为全区一致变化型,且在1989年发生了年代际突变,突变后(前)为偏旱(涝)期。热带东印度洋—西太平洋和北大西洋的海表温度年代际升高对重庆秋季年代际干旱具有重要作用,热带东印度洋—西太平洋为关键海区,北大西洋为次关键海区。热带东印度洋—西太平洋关键海区的海表温度异常影响重庆秋季年代际干旱的可能机制为:当该区海表温度秋季年代际增暖时,西北太平洋副热带高压位置西伸北抬、面积偏大、强度增强,重庆地区位势高度升高,孟加拉湾南支槽减弱,不利于水汽从孟加拉湾向重庆地区输送,同时赤道地区存在异常上升运动,使得区域Hadley环流增强,重庆地区为异常下沉区,由此导致重庆地区年代际干旱。北大西洋次关键海区的海表温度异常影响重庆秋季年代际干旱的可能机制为:当该区海表温度秋季年代际增暖时,西北太平洋副热带高压偏北,重庆地区位势高度升高且有异常下沉运动,从而导致重庆地区年代际干旱。上述观测结果由应用NCAR CAM5.1全球大气环流模式进行的关键海区海表温度年代际变化敏感性试验得到验证。

Based on the precipitation and temperature data of 30 observation stations in Chongqing,NCEP / NCAR reanalysis data and NOAA ERSST v3 b during 1961—2012,this study uses the standardized precipitation evapotranspiration index（ SPEI） computed by temperature and precipitation data to discussthe interdecadal variability feature of autumn drought in Chongqing and its possible causes. Observational results show that main distribution of Chongqing autumn SPEI is in the same phase and its interdecadal shift happens in 1989. After（ before） this shift,Chongqing gets drier（ wetter） than normal. It is also found that the tropical eastern Indian Ocean and western Pacific（ EIWP） and the North Atlantic（ NA） are both key areas,where the interdecadal increases of sea surface temperature anomaly（ SSTA） play important roles in interdecadal autumn drought in Chongqing,and EIWP is more important than NA. Their possible mechanisms of effect of SSTA in the two key areas on the interdecadal autumn drought in Chongqing are investigated. When autumn SST in EIWP is warmer than normal on interdecadal time-scale,the northwestern Pacific subtropical high（ NWPSH） will get larger and stronger than usual,and extend westward and northward,resulting in higher geopotential heights over Chongqing and weaker south branch trough（ SBT）over the Bay of Bengal. These circulation anomalies will be not favorable to water vapor transport from the Bay of Bengal to Chongqing. There exists an anomalous upward motion around the key area,inducing an enhanced regional Hadley cell across Chongqing,and then an anomalous downward motion controls Chongqing,resulting in the interdecadal drought. When autumn SSTA in NA is warmer than normal on interdecadal time-scale,the NWPSH will extend northward,resulting in higher geopotential heights and an anomalous downward motion over Chongqing,which causes the interdecadal drought. The above observational results are verified by the sensitive experiments on effect of SSTA in the two key areas on the interdecadal drought,which are conducted by NCAR CAM5. 1（ Community Atmosphere Model 5. 1）.