Diverse impacts of <scp>ENSO</scp> on wintertime rainfall over the Maritime Continent

Abstract

ABSTRACT The diverse influences of the El Niño Southern Oscillation ( ENSO ) on wintertime precipitation over the Maritime Continent are herein investigated using observational data. The ENSO events are divided into four categories—strong El Niño, strong La Niña, moderate El Niño and moderate La Niña—according to their amplitudes. Significant negative Maritime Continent precipitation anomalies are observed during strong El Niño events, whereas wet conditions occur during strong La Niña events. In the case of moderate La Niña events, the Maritime Continent rainfall anomalies are similar in spatial structure and comparable in amplitude to strong La Niña events, whereas almost no significant rainfall anomalies are observed in moderate El Niño years. Further analysis shows that strong El Niño (strong/moderate La Niña) events are associated with a significant anticyclone (cyclone) surface response over the western tropical Pacific and related to a significant descending (ascending) branch of the Walker circulation around the Philippines. However, during moderate El Niño events, both the central‐eastern and the western tropical sea surface temperature anomalies ( SSTA ) are weak and cannot significantly change the Walker circulation over the tropical Pacific. Therefore, the descending branch anomalies of the Walker circulation associated with moderate El Niño events around the Philippines are quite weak and cannot cause significant negative precipitation anomalies in that location. In addition, there is large case‐to‐case variance in the tropical Pacific SSTA associated with moderate El Niño events, which also contributes to the weak Maritime Continent rainfall response in the composite analysis.