Mechanisms of Malaysian Rainfall Anomalies

Abstract

The behavior of the Malaysian anomalous rainfall is examined in relation to the El Niño?Southern Oscillation (ENSO) and local air?sea influences. The behavior is consistent with the northward migration of the ENSO-related coherence in the Maritime Continent rainfall. During the June?July?August (JJA) period, the ENSO-related coherence is low in the Malaysian rainfall but higher in the Indonesian rainfall. During the September? October?November (SON) period, the behavior of Malaysian anomalous rainfall is similar to that of the Indonesian rainfall since the ENSO-related coherence progresses northward to include the Malaysian region. It is proposed that a mechanism that operates during this period is similar to that in Indonesia, where local anomalous sea surface temperatures (SSTs) act to strengthen the remote influence of anomalous SST associated with ENSO in the eastern central Pacific. However, during the December?January?February (DJF) period, the behavior is markedly different from that of the Indonesian rainfall. During this period, the ENSO-related coherence has shifted northward across the equator. This shift results in the strengthening of ENSO?Malaysia rainfall relationship and the weakening of ENSO?Indonesia rainfall relationship. It is proposed that a different mechanism in which the anomalous cyclonic circulation over the South China Sea, northern Borneo, and the Philippine Sea is directly responsible for modulating the anomalous Malaysian rainfall during the DJF period. Finally, it is postulated that the anomalous cyclonic circulation is a response to the SST dipole associated with the strengthening of the northern arm of the boomerang-shaped SST in the northwestern Pacific Ocean.