Summary of Abstract Submission

Abstract Submission No. IO50-07-0026PresentationOral


Claudia E. Wieners*1, Wilhelmus P.M. de Ruijter1, Henk A. Dijkstra1

1 Utrecht University, Netherlands


A Multichannel Singular Spectrum Analysis (MSSA) of observational SST and zonal wind data suggests that the tropical Indian and Pacific Oceans behave as a coherent multi-basin coupled system on ENSO time scales. In particular, the SST in the Seychelles Dome (SD) region in late boreal summer is negatively correlated to Nino3.4 after ca 1.5 years. The correlation is significant against the null hypothesis that it is caused by the cyclicity of ENSO and ENSO¿s influence on the SD. In particular, a cool SD favours El Niño events with a strong signal in the East Pacific, starting at the Peruvian coast and growing westward. Observations suggest two explanations: First, subsidence above a cool SD induces enhanced convection in Indonesia. The resulting easterly inflow from the Pacific favours the creation of a large Pacific Warm Water Volume which can be released into the East Pacific in the following boreal spring/summer - a prerequisite for East Pacific El Niño events. Second, a cool SD favours a strong intraseasonal zonal wind variability above the West Pacific, part of which can be attributed to influence of the SD on the Madden-Julian Oscillation. This wind variability induces downwelling Kelvin waves which can initiate El Niño. Currently we are investigating these observations further, using dedicated GCM experiments and an intermediate complexity model (a double-basin extension of the Zebiak-Cane model).