印度洋海表温度的变化及其对印度夏季季风降水影响的诊断研究
Diagnostic study of the variation of Indian Ocean sea surface temperature and its impact on Indian summer monsoon rainfalls
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摘要: 对印度洋海表温度(SST)的主要特征及变化趋势进行分析,并研究了其与印度夏季季风降水(ISMR)和季风环流的关系,揭示出:从北印度洋到南半球中高纬度印度洋,SST最显著的变化模态是全海盆一致的变化,近50 a来总体趋势是上升的,在1976,1986年以及1996年间分别有一次跳跃性增温,与太平洋SST变化趋势基本一致.除了长期变化趋势外,南印度洋中高纬度比热带地区有更显著的模态分布.在印度洋SST升温的背景下,ISMR具有逐渐减少的趋势,但两者相关较弱.印度洋SST发生跳跃后的不同阶段,许多海区SST与ISMR相关均发生变化,但在春季,热带外南印度洋具有一对相对稳定区,其分布与EOF分析的第2模态相似.根据它们的分布,文中定义了春季南半球偶极子(SIOD),在正SIOD(PSIOD)情况下印度降水偏多,而负SIOD(NSIOD)则反之.环流分析表明,PSIOD(NSIOD)通过与大气的相互作用,对夏季马斯克林高压具有增强(减弱)作用,进而使得索马里越赤道气流增强(减弱),在印度地区低空产生异常的辐合(辐散),高层辐散(辐合),从而影响印度季风环流,使得印度季风降水偏多(少).Abstract: The major modes and variations of Indian Ocean (IO) sea surface temperature (SST) and relationship with Indian Summer Monsoon Rainfalls (ISMR) are analyzed.The results show that the most significant mode of IOSST in recent 50 a is the warming trend at most of the ocean basin and there is abrupt warming in 1976, 1986 and 1996 respectively.The warming trend of IOSST has weak relationship with the decreasing trend of ISMR.During the different backg rounds after the leaps of IOSST, the relationship of ISMR between SST had changed in many regions but rather stable in extrat ropical IO.The stable correlation distribution is similar to the second mode of Indian Ocean SST EOF analysis and named as South Indian Ocean Dipole (SIOD).ISMR generally increase during positive SIOD (PSIOD) years and decrease during negative SIOD (NSIOD) years.The general circulation analysis shows, during PSIOD (NSIOD) phase, the SST anomalies of extratropcical IO will enhance (weaken) the Mascarene high by interacting with regional atmosphere, then enhance (weaken) the cross equatorial flow off Somali, produce convergence (divergence) at low level and divergence (convergence) at high level over India, and finally lead the ISMR increasing (decreasing).
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