Sensitivity of South American summer rainfall to tropical Pacific Ocean SST anomalies

摘要

A suite of idealised ensemble experiments are used to investigate the sensitivity of the Southern Hemisphere atmospheric circulation to the location of SST anomalies over the tropical Pacific Ocean. Of particular interest is the response of South American rainfall during austral summer. The experiments reveal an approximately opposite response in rainfall over South America when the tropical SST forcing is applied over the western and eastern Pacific Ocean, respectively. The contrasting tropical rainfall conditions are due primarily to the displaced Walker circulation anomalies. Further south, the atmospheric circulation over the South American subtropics is modulated by teleconnection patterns that appear as a wave train. The resulting circulation manifests as an anomalous cyclone over central-eastern South America which in turn leads to a northward displacement of the westerly moisture transport when the SST forcing is located further west. The opposite pattern occurs when the SST forcing is applied to the eastern equatorial Pacific.