On possible impact of the Indian summer monsoon on the ENSO

Abstract

The Indian summer monsoon (ISM) could influence the El Nino and Southern Oscillation (ENSO) only if it could induce significant surface wind anomalies in the active regions of central and eastern equatorial Pacific. Using 50-year NCEP reanalysis, it is shown that observed surface winds in the central and eastern Pacific associated 'purely' with ISM and unrelated to ENSO are very weak (~0.5m.s^-1). Strong surface winds in the central and eastern Pacific following a 'strong' or 'weak' ISM, noted in some earlier composite analyses, are related not to ISM but to the concurrent sea surface temperature (SST) forcing associated with the ENSO. A long run of an atmospheric general circulation model (AGCM) without inter-annual SST forcing also show that a 'pure' ISM induces only very weak surface winds in the equatorial central and eastern Pacific. Thus, we conclude that the ISM by itself is unlikely to influence the ENSO in a significant way.