Interdecadal changes in the El Nino-La Nina asymmetry

The SST anomalies (SSTA) over the past 148 years have been analyzed to describe the interdecadal change in the skewness of SSTA (ICS) in the tropical Pacific and possible consequence of this change. The first EOF mode of ICS represents the interdecadal changes in the El Nino-La Nina asymmetry. The corresponding PC time series is related to the ENSO predictability, suggesting that ENSOs are more predictable during the positive ICS decades than during the negative ICS decades, and to the propagation characteristics of ENSO such that SSTA during the positive (negative) ICS decades tend to propagate eastward (westward). Moreover, ICS was found to be associated with interdecadal SST variations in the tropical eastern pacific, suggesting a nonlinear positive feedback between ENSO variability and mean climate change. The ICS also is negatively correlated to SSTA over the northern midlatitude oceans and positively correlated to those over the southern midlatitude oceans.