El Niño-La Niña dynamics over Southeast Asia

Abstract

During the past two decades, the Philippines has experienced unusual droughts and floods due to the climatological phenomena called El Niño and La Niña. El Niño occurs approximately once every five years, while La Niña is less frequent. El Niño is a physical event that is generated by anomalously warm sea surface temperatures (SST) over the Central and Eastern Pacific Ocean. The abnormally warm SSTs and overlying air cause changes in the large-scale atmospheric circulations. Normal convergence zones of moisture are shifted during El Niño events causing widespread modifications in the amount of rainfall over certain regions in the Pacific.
For example, in India and Indonesia, below normal rainfall is observed. The same happens in Brazil and in Australia. On the other hand, these episodes produce above normal rainfall in Sri Lanka, Peru, and Ecuador. In Southeast Asia, the frequency and tracks of tropical cyclones are known to be affected. Preliminary analyses indicate that there are less tropical cyclones during El Niño. Furthermore, the tracks of cyclones are displaced generally northward. More detailed descriptions of the effects of El Niño are described by Hastenrath.
In general, the opposite happens during the La Niña period. It occurs during periods of abnormally cold SST over the Central and Eastern Pacific. Usually, where there were droughts during the El Niño, floods occur.
Over the years, these two phenomena have been studied extensively over many regions of the globe. In Southeast Asia, however, there have been extremely few studies done. This paper is an observational and diagnostic study of the dynamics and impact of El Niño and La Niña in Southeast Asia.