On possible impact of the Indian summer monsoon on the ENSO

The Indian summer monsoon (ISM) could influence the El Nino and Southern Os cillation (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 centra l and eastern Pacific associated 'purely' with ISM and unrelated to ENSO ar e very weak (similar to 0.5m.s(-1)). Strong surface winds in the central an d eastern Pacific following a 'strong' or 'weak' ISM, noted in some earlier composite analyses, are related not to ISM but to the concurrent sea surfa ce temperature (SST) forcing associated with the ENSO. A long run of an atm ospheric general circulation model (AGCM) without inter-annual SST forcing also show that a 'pure' ISM induces only very weak surface winds in the equ atorial central and eastern Pacific. Thus, we conclude that the ISM by itse lf is unlikely to influence the ENSO in a significant way.