Occurrence of two types of El Niño events and the subsurface ocean temperature anomalies in the equatorial Pacific

Abstract

The relationships between the evolution of two types of El Nino events and the subsurface ocean temperature anomaly (SOTA) in the equatorial Pacific are compared in this study. The results show that both types of El Nino are negatively correlated to the SOTA in the equatorial western Pacific, but relationships are different in different phases of El Nino. Furthermore, the occurrence of different types of El Nino is related to different features of the equatorial thermocline, e.g. its zonal gradient, significant variation area, amplitude and duration of thermocline oscillation. The propagation of SOTA in the equator plays an important role during the evolution of both types of El Nino, but shows dramatic differences in intensity, duration and phase reverse of warm SOTA. Moreover, the pathways of SOTA signal are different between these two types of El Nino. The dominant pathway in the life cycle of Eastern Pacific (EP)-El Nino lies on the equator and to its north, but there is no loop to the south of the equator. In contrast, the dominant pathway in Central Pacific (CP)-El Nino is located on the equator and to its south, and the propagation signal of SOTA to the north of the equator is very weak. The relationships between the zonal wind anomalies and the two types of El Nino are also preliminarily discussed. It is shown that EP-El Nino is more likely to respond to the westerly anomalies over the equatorial central and western Pacific, while CP-El Nino is more likely to respond to the westerly anomalies over the equatorial western Pacific and need the cooperation of easterly anomalies over the equatorial eastern Pacific to certain extent.