The negative feedback effects of sea surface temperatures on El Niño Events in the West Indian Ocean

Abstract

In this study, multiple sets of atmospheric and oceanic observational data were used in combination with composite analysis and correlation analysis methods, in order to analyze the anomalous eastward spread phenomena of the equatorial Indian Ocean during the autumn and winter seasons when El Niño events have previously occurred. The analysis results showed that anomalous increases in the SSTs (sea surface temperatures) in the West Indian Ocean during the early autumn seasons had triggered the responses of anomalous easterlies. Meanwhile, anomalous anticyclonic circulation was observed to have existed on the north side of the easterlies. It was found that with the maximum center of the specific humidity retreating toward the vicinity of the equator during the processes of the seasonal conversion, the asymmetry of moisture advection on the eastern and western sides of the anomalous anticyclonic circulations tended to lead to the circulation systems to move in an eastward direction until reaching the Northwest Pacific region. During the winter seasons with peak periods of El Niño events, the easterly anomalies in the equatorial West Pacific Ocean were found to stimulate the upturning Kelvin fluctuations in the ocean. This resulted in eastward spreading actions which eventually helped the El Niño events to transform into La Niña events.