On the Surface Independent Signals Within the ENSO Events

By analyzing the two types of El Nino Southern-Oscillation (ENSO) indices, i.e., the Central Pacific (CP) type index and the Eastern Pacific (EP) type index by Ren and Jin (2011), this study finds that the low correlation between the two types of indices by some previous studies should be reconsidered. Then based on previous ideas of the unified Nino index systems, the new ocean surface regions for the CP and EP El Nino indices’ calculation are defined. The features of the new CP and EP El Nino indices are consistent with sea surface temperature anomaly (SSTA) evolution along the Pacific equator. This study suggests that, concerning the El Nino characteristics, the CP and EP El Nino indices are not necessarily independent of each other; but their differences are almost absolutely independent of the unified Nino region SSTA. The results quantitatively confirm the relationship between the Trans-Nino Index (TNI) and Nino 3.4 indices (which are nearly independent of each other and provide different flavors for each El Nino event). Results presented here contribute to a better understanding of the nature of the El Nino events.