热带印度洋偶极子与中国夏季年际气候异常关系的年代际变化

利用中国站点观测逐月降水和月平均气温资料以及NCEP/NCAR再分析资料,揭示了热带印度洋偶极子(IOD)与中国夏季气候异常关系的年代际变化.结果表明:IOD与中国夏季年际气候异常的关系既有稳定的一面,又存在着年代际变化.较为稳定的关系表现为:IOD与同年夏季长江黄河之间的降水变化存在显著负相关,与四川气温变化存在显著正相关;IOD与次年夏季四川降水存在显著正相关.伴随发生在20世纪70年代末的大尺度环流年代际转型,IOD与中国气候年际异常的联系亦发生变化:IOD正位相年的同年夏季降水异常型,由中国大部分地区偏少变为长江以南(北)偏多(少),气温由西南地区东部偏暖变为长江以南(北)偏冷(暖);次年夏季降水由全国大部分地区偏多变为长江以南(北)偏少(多),气温由全国大部分地区相关不显著变为黄河以南大部分地区显著偏暖.在IOD负位相年,中国夏季气候异常的特征与IOD正位相年相反.在20世纪70年代末的大尺度年代际气候转犁前后,与IOD相关的东亚大气环流异常特征明显不同.在IOD发展阶段,在70年代末以前,印度夏季风和南海季风偏强,副热带高压势力偏弱,导致中国华南大部分地区降水偏少,华北西部以及内蒙古中部等地降水偏多;70年代末以后,东亚大陆中纬度为弱的东风距平,导致新疆北部降水偏少,气温偏高,华南降水偏多.在IOD次年夏季,70年代末以前,华南、河套以及四川等地盛行偏南气流,降水偏多;70年代末以后,南亚高压和西太平洋副高偏西偏强,华南、江南降水偏少.

Interdecadal change of the relationship between tropical Indian Ocean dipole and anomalous summer climate in China

Interdecadal changes of the relationship between tropical Indian Ocean dipole(IOD) and the interannual variability of summer climate in China are investigated by using the technique of sliding correlation analysis with the monthly tropical Pacific SSTA and the monthly surface air temperature and precipitation of the NCEP/NCAR reanalysis data and the station-observed data in China during 1957-2005. The results indicate that the relation between IOP and summer climate anomaly in China on one hand showed a stable robust aspect, and on the other hand interdecadal changes. The stable relation manifested mainly in the significant negative correlation between IOD and summer precipitation in the Changjiang-Huaihe River valley, the distinctive positive correlation between IOP and summer air temperature in Sichuan, and the remarkable positive correlation between IOD and next summer precipitation in Sichuan. Accompanied with the interdecadal shift of the large-scale general circulation pattern in the late 1970s, the association of IOD and interannual variability of summer climate in other regions in China also changed. From the pre-shift to the post-shift epoch, during the development phase of positive IOD, the summer precipitation anomaly pattern in China changed from below normal in most of China to above (below) normal in areas south (north) of Changjiang River, and the summer surface air temperature anomaly pattern changed from warming in the east of Southwest China to cooling (warming) in areas south (north) of Changjiang River; and in the next summer of positive IOD, the precipitation anomaly pattern in China changed from above normal in most of China to below (above) normal in areas south (north) of Changjiang River, and the temperature anomaly pattern from no significant correlation in most of China to significant warming in most areas south of Huanghe River. Based on the composite analysis of the NCAR/NCEP reanalysis dataset, significant different IOD-related atmospheric circulation anomalies in East Asia over the pre-shift and post-shift epoch may be responsible for the interdecadal change of relationships between IOD and summer surface air temperature and precipitation in China. During the development phase of positive IOD, before the late 1970s, the Indian summer monsoon and South China Sea summer monsoon were stronger and the subtropical high was weaker than normal, which led to less precipitation in most of South China but more precipitation in western North China and middle Inner Mongolia; after the late 1970s, easterlies were weaker over middle East Asian, which resulted in less precipitation and higher temperature in northern Xinjiang and excessive precipitation in South China. During the summer in the next year of positive IOD, before the late 1970s, southerlies prevailed over South China, Hetao and Sichuan, bring about more precipitation, and after that time, South Asian high and northwestern Pacific subtropical high were stronger and extended westwards, which caused deficit precipitation in South China and Jiangnan.