South Pacific origin of the decadal ENSO-like variation as simulated by a coupled GCM

Abstract

The hypothesis of the South Pacific origin of the decadal (7-35 years) ENSO-like variation is investigated based on 200-year outputs of the ECHAM4/OPA/OASIS coupled GCM. Associated with the decadal warm (cold) SST anomalies in the tropical Pacific, an anomalous cyclonic (anticyclonic) circulation, which is tilted in a southeast-northwest direction, appears in the South Pacific. This results in anomalous upward (downward) Ekman pumping along the northeastern edge of the anomalous circulation and, hence, shallowing (deepening) the oceanic thermocline there. Such an external source of heat content tends to slowly discharge/recharge the tropical ocean on the decadal timescale. The above result is consistent with the observational study of Luo and Yamagata [2001]. Besides, the model reproduces amazingly a high lagged-correlation between the global land surface temperature and the decadal Nino3 SST. Despite the model biases, this suggests a potential prediction skill of the global warming based on the ENSO-like decadal variation. Copyright 2003 by the American Geophysical Union.