Quantifications of the Two “Flavours” of El Niño using Upper-Ocean Heat Content

AbstractThe sea surface temperature (SST) or sea level pressure (SLP) has usually been used to measure the strength of El Nino–Southern Oscillation (ENSO) events. In this study, two new indices, based on the upper-ocean heat content (HC), are proposed to quantify the two “flavours” of El Nino (i.e., the Cold Tongue El Nino (CTE) and Warm Pool El Nino (WPE)). Compared with traditional SST or SLP indices, the new HC-based indices can distinguish CTE and WPE events much better and also represent the two leading modes of the interannual variability of the atmosphere–ocean coupled system in the tropical Indo-Pacific region. The two leading modes are obtained by performing multivariate Empirical Orthogonal Function analysis on two oceanic variables (SST and HC) over the tropical Pacific (30°S–30°N, 120°E–80°W) and six atmospheric variables (outgoing longwave radiation, SLP, streamfunction, and velocity potential at 850 hPa and 200 hPa) over the tropical Indo-Pacific region (30°S–30°N, 60°E–80°W) for the period ...