Monsoon/El Niño‐Southern Oscillation relationships in a simple coupled ocean‐atmosphere model

Abstract

A coupled ocean‐atmosphere model is used to investigate the equatorial Indian and Pacific Oceans' response to the seasonally varying monsoon winds and the relationship between monsoon variations and the El Niño‐Southern Oscillation phenomenon (ENSO). The atmosphere is a simple linear shallow water system driven by a mass source/sink term that is proportional to the sea surface temperature (SST) over the oceans and the heat balance over land. The ocean is modeled using the Anderson and McCreary [1985] reduced‐gravity transport model driven by atmospheric wind stress forcing and a parameterized heat flux. The model domain includes both the Indian and Pacific Oceans and land masses to represent Asia and Africa. Results show that variations in the model's monsoon circulation (evolving somehow from other influences) induce changes in the large‐scale circulation associated to ENSO. In this way the year‐to‐year differences in the monsoon impact on the longer‐period, coupled ocean‐atmosphere dynamics of the near‐equatorial Pacific basin. By changing the amplitude of the monsoon forcing the interval between ENSO‐like warm events varies, while the variability in the annual cycle over the Indian Ocean is hardly affected.