Impact of El Niño on the East Asian Monsoon

Abstract

The East Asian monsoon circulation during the El Nino episodes of '86/87 and '91/92 is studied diagnostically. It is found that a southerly wind anomaly appeared in the lower troposphere along the coast of the East Asia during the mature phases of these two El Nino events. In the case of '86/87, the mature phase covered the boreal summer and the East Asian summer monsoon was intensified. On the other hand, in the case of '91/92, the northern winter was within the mature phase and the East Asian winter monsoon was weakened. Examination of the circulation features suggests that the effects of the El Nino events on the East Asian monsoon are felt through the variation of convective activities over the western equatorial Pacific. Convections in this area are strongly influenced by the evolution of sea surface temperature anomalies in the equatorial Pacific and are strongly suppressed during the mature phase, which exerts significant influences on the direct monsoonal circulation over the western tropical Pacific and the East Asia. The relationship between the East Asian monsoon and El Nino in its mature phase is also confirmed by a historical 850hPa wind dataset that covers 6 events prior to the '86/87 event. The dataset also suggests that an inverse relationship does not hold during the La Nina periods.