Joint Modes of the Pacific-Indian Ocean Sea Surface Temperature Anomaly at Interannual Timescale

Based on the monthly mean sea surface temperature data removing linear trend from HadiSST during 1870 to 2004,two joint modes of the Pacific-Indian Ocean sea surface temperature anomaly at interannual timescale were analyzed with the application of the Season-reliant empirical orthogonal function(S-EOF) decomposition method.Results show that the low-frequency ENSO is the leading ajoint mode accompanying with the Indian Ocean basin mode.An anomalous anticyclone is hold over the equatorial Indian Ocean,which can weaken the Indian summer monsoon and transport the warm water in the eastern Indian warm pool to the west,further causes the Indian Ocean basin warming in all four seasons.The second joint mode is the transition mode of the ENSO with the India Ocean dipole mode.The phase of ENSO begins to change in boreal spring,when the monsoon is in the transition stage.Accordingly,an anomalous cyclonic cell appears over the India Ocean,which can enlarge the east-west SST difference of the equatorial Indian Ocean by enhancing the Indian summer monsoon.Based on the fact,the eastern Indian Ocean warming reaches its maximum in boreal autumn and a dipole mode appears.The India Ocean summer monsoon is closely related to the development of this mode.