热带印度洋海温的年际异常及其海气耦合特征

利用长期观测资料分析了印度洋海温距平的年际变化及其海气耦合特征,结果表明热带印度洋海温距平的变化存在显著的距平符号东西一致的单极型和距平符号东西相反的偶极型,其出现的概率分别为67%和33%.偶极期间在热带印度洋和西太平洋海洋性大陆上空的大气中存在着明显的Walker类型的环流,具有显著的局地海气耦合特征,而单极期间这种特征不明显.大部分偶极子的生命史都非常短暂,其持续发展的主要特征表现为西印度洋正距平的增加、东移和东印度洋负距平的不断加强.单极的发展为整个海盆的不均匀增暖.单极向偶极的转换可以分为两类,第I类表现为赤道西印度洋海表温度距平由负转变成正后逐渐向东扩展,东印度洋的负距平范围逐步缩小;第II类是东南印度洋海表温度的负距平不断加强并略向西发展,而西部保持正距平.这种转换还经历了一个年代际变化,20世纪70年代中后期以前主要是第I类转换,以后则第II类占绝大多数.

Features of the Interannual Variation of Sea Surface Temperature Anomalies and the Air-Sea Interaction in Tropical Indian Ocean

A diagnostic analysis is carried out to investigate the interannual variation of the sea surface temperature anomalies (SSTA) and the characteristics of the air-sea interaction in the tropical Indian Ocean. The results show that the spatial distributions of SSTA are characterized by unipole with the same anomalous signs in basin-scale or by dipole with the reverse west-east counterparts. The occurrence probability of the unipole and dipole are 67% and 33%, respectively. During the dipole episode, the local ocean and atmosphere are coupled strongly with a prominent Walker-type atmospheric circulation over the tropical Indian Ocean, which are not obvious during the unipole. Most dipole events last short and develop commonly by the feature of the increase, eastward migration of the positive SSTA in the western Indian Ocean and the enhancement of negative SSTA in the eastern Indian Ocean. The unipoles, on the contrary, warm unevenly in the basin. The transitions from unipole to dipole can be sorted to be two types. The first type is characterized by the changing of SSTA from the negative to the positive and then eastward moving of the positive SSTA in the west and the shrink of the negative SSTA in the east. The second type is featured by the continually reinforcing and slightly westward shifting of the negative in southeast Indian Ocean and the maintaining of the positive in the west. The transitions underwent an interdecadal variation. The first and second types dominate before and after the mid-late 1970s, respectively.