Interannual Variation of the Tropical Indian Ocean Sea Surface Temperature Pre-and Post-1976/1977

Based on 58-year(1948-2005) NCEP/NCAR reanalysis data,interannual variation of the tropical Indian Ocean sea surface temperature pre-and post-1976/1977 is studied.The original data are filtered to retain the variation with periods from 13 months to 8 years.The results show that ENSO could cause a basin-wide warming/cooling mode with the strongest phase in winter in the tropical Indian Ocean which lags ENSO 2-6 months both pre-and post-1977.But the mode pre-1977 is stronger than that post-1977.The former leads the latter two months in phase.Prior to 1977,the dominant mode of the tropical Indian Ocean SSTA(SST anomaly) in autumn appeared as a basin-wide uniform pattern.After 1977,however,the dominant mode appeared as a dipole or zonal gradient pattern.Changes in the response of the Indian Ocean surface wind to ENSO pre-and post-1977 account for the shift of dominant mode.Prior to 1977,the ENSO-related anomalous tropical Indian Ocean surface easterly firstly appeared in summer.After 1977,however,it appeared firstly in spring and a strong anticyclone dominated the southern tropical Indian Ocean throughout the season.