Response of the Antarctic sub-polar jet and the Southern Annular Mode to the El-Nino and La-Nina forcing in the Austral Summer Season

Abstract

The responses of the Antarctic SPJ and the associated SAM to gradually increasing ENSO forcings are investigated for austral summer. Through a series of numerical experiments, we show that SPJ do not respond to a moderate ENSO forcing, but instead respond exponetially only to strong ENSO through the changes in eddy activities. It can be inferred how the eddy-induced change in westerly flow accompanies the negative SAM phase for only extreme El- Nino periods. That is, if the tropical SST forcings are moderate, eddy-induced changes in westerly flow are too small to accompany the changes in the SAM phase. However, when the SST forcing are strong enough, the SPJ responses to the eddy activities associated with the SST forcing can be reflected in the negative SAM phase.