Features of the Interannual Variation of Sea Surface Temperature Anomalies and the Air-Sea Interaction in Tropical Indian Ocean
热带印度洋海温的年际异常及其海气耦合特征

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.