Decadal amplitude modulation of two types of ENSO and mean state changes

In this study, we analyze the decadal amplitude modulation of ENSO (El Nino-Southern Oscillation) using a 500-yr simulation of the GFDL CM2.1. Especially, we focus on the occurrences of the two types of ENSO within the modulation cycle. Composite analyses show the asymmetries between El Nino and La Nina events in terms of the spatial pattern and magnitude. In the strong (weak) ENSO amplitude decades, the El Nino centers in the eastern (central) tropical Pacific and La Nina in the central (eastern) tropical Pacific. The El Nino events in strong ENSO amplitude decade are similar to the conventional El Nino. On the other hand, the El Nino events in weak ENSO amplitude decade resemble the new-type of El Nino which is named by Central Pacific El Nino, Warm Pool El Nino, Dateline El Nino, or El Nino Modoki. In addition, we examine a nonzero residual effect induced by the El Nino-La Nina asymmetries on the changes in the Pacific mean state.