中国春季降水与南印度洋偶极子的关系研究

RELATIONSHIP BETWEEN THE SPRING RAINFALL IN CHINA AND DIPOLE OSCILLATION IN THE SOUTHERN INDIAN OCEAN

利用美国国家海洋和大气管理局海温资料和1951~2010年中国160站月降水量资料,分析了前期冬季(12~2月)印度洋海表温度与中国160站春季降水的关系及其影响机制。研究表明:冬季印度洋海温异常的空间模态主要有两种:符号一致的单极和东、西符号相反的南印度偶极。将第2模态的时间系数定义为南印度洋偶极子指数。该指数与中国次年春季降水关系较好,并利用NCEP/NCAR再分析资料进行机制分析,发现主要南印度洋偶极子通过以下途径影响中国春季降水:中高纬,SIOD的影响主要引起低纬度的海温及对流异常,通过中低纬度间的相互作用,在中高纬产生较强的遥响应,从而影响同期冬季欧亚大陆的环流变化,这种扰动在西风气流的作用下引起后期春季北太平洋地区对流活动异常,通过中低纬度间的相互作用,加强中高纬地区的遥响应,表现为欧亚大陆EUP波列;低纬,SIOD的影响主要引起南海-海洋性大陆的海温及对流异常,引发经向环流异常,导致黄河至长江中下游地区垂直运动异常和气流辐合异常。

Based on the National Center for Environmental Prediction/National Center for Atmospheric Research(NCEP/NCAR)reanalysis data and the precipitation data from 160stations in China,the relationship and influence mechanism between the Indian Ocean sea surface temperature(SST)in winter and Chinese 160-station rainfalls during the next spring are investigated.The empirical orthogonal function analysis results show that the spatial distributions of winter SST anomalies(SSTA)in the Southern Indian Ocean are characterized by monopole with the same anomalous signs in basin-scale and by dipole with the reverse signs in the western and eastern Southern Indian Ocean.The second time series of the dipole mode are defined as Southern Indian Ocean dipole(SIOD)index.When the area-averaged SST anomalies are positive in West Pole and negative in East Pole,apositive SIOD happens.While the area-averaged SST anomalies are negative in West Pole and positive in East Pole,a negative SIOD happens.The impact of SIOD on the rainfalls in the next spring in China is greatest.In positive SIOD years,the rainfalls are subdued over the Yangtze River and its north in the next spring.While in negative SIOD years,the rainfalls increase over the Yangtze River and its north in the next spring.The relationship is independent of ENSO events.Based on the reanalysis data,using synthesis and related method,we find that SIOD influence on the spring rainfall in China through the joint action of high latitudes and low latitudes.SIOD induces low latitude sea surface temperature and convection anomalies.Through interaction between middle and low latitudes,the anomalies cause strong remote response in the middle and high latitudes,thus affect the same period of circulation changes in winter Eurasia.By the effect of the westerly flow,such perturbations cause the anomalous convective activity in the North Pacific in the next spring.Also through interaction between middle and low latitudes,it strengthens the remote response of the middle and high latitudes,and EUP wave train happens.The convection anomalies in the South China Sea and Sea Maritime Continent caused by SIOD,induce meridional circulation anomalies and vertical motion abnormalities over the Yellow River to the Yangtze River region.Under the joint action of high latitudes and low latitudes,the abnormal rainfall in China happens.