North Pacific premonitory sign of the ENSO event

Abstract

The premonitory sign of the ENSO event shows up in the North Pacific subtropical Mode Water (STMW) 18 months earlier, and this should be useful in forecasting the occurrence of this important phenomenon. The premonitory connection involves an air-sea coupling between the longtime persistent mid-latitude SSTA induced by the remote re-emergence of STMW and the following spring subtropical atmospheric circulation anomalies. Examination of the air-sea interaction reveals that the following spring subtropical atmospheric circulation which responds to the longtime persistent SSTA is dominated by the anomalous negative (positive) geopotential height downstream of the negative (positive) SSTA in the strong (weak) STMW case. Then, the tropics adjust to these anomalies through coupled dynamics, producing ENSO-like pattern of variability. Details of the connection and possible process are presented. Copyright 2009 by the American Geophysical Union.