The Coupled GCM ECHO-2. Part II: Indian Ocean Response to ENSO

The interannual variability of the Indian Ocean SST is investigated by analyzing data from observations and an integration of a global coupled GCM (CGCM) ECHO-2. First, it is demonstrated that the CGCM is capable of producing realistic tropical climate variability. Second, it is shown that a considerable part of the interannual variability in Indian Ocean SST can be described as the response to interannual fluctuations over the Pacific related to ENSO. Although the Indian Ocean region also exhibits ENSO-independent interannual variability, this paper focuses on the ENSO-induced component only. Large-scale SST anomalies of the same sign as those observed in the eastern equatorial Pacific Ocean during ENSO extremes develop in the entire tropical and subtropical Indian Ocean with a time lag of about 4 months. This lead–lag relationship is found in both the observations and the CGCM. Using the CGCM output, it is shown that the ENSO signal is carried into the Indian Ocean mainly through anomalous surface heat fluxes