El Niño–Related Summer Precipitation Anomalies in Southeast Asia Modulated by the Atlantic Multidecadal Oscillation

Abstract

AbstractHow the Atlantic multidecadal oscillation (AMO) affects El Niño–related signals in Southeast Asia is investigated in this study on a subseasonal scale. Based on observational and reanalysis data, as well as numerical model simulations, El Niño–related precipitation anomalies are analyzed for AMO positive and negative phases, which reveals a time-dependent modulation of the AMO. 1) In May–June, the AMO influences the precipitation in southern China (SC) and the Indochina peninsula (ICP) by modulating the El Niño–related air–sea interaction over the western North Pacific (WNP). During negative AMO phases, cold sea surface temperature anomalies (SSTAs) over the WNP favor the maintaining of the WNP anomalous anticyclone (WNPAC). The associated southerly (westerly) anomalies on the northwest (southwest) flank of the WNPAC enhance (reduce) the climatological moisture transport to SC (the ICP) and result in wetter (drier) than normal conditions. In contrast, during positive AMO phases, weak SSTAs over the WNP lead to limited influence of El Niño on precipitation in Southeast Asia. 2) In July–August, the teleconnection impact from the North Atlantic is more manifest than that in May–June. During positive AMO phases, the warmer than normal North Atlantic favors anomalous wave trains, which propagate along the “great circle route” and result in positive pressure anomalies over SC, consequently suppressing precipitation in SC and the ICP. During negative AMO phases, the anomalous wave trains tend to propagate eastward from Europe to Northeast Asia along the summer Asian jet, exerting limited influence on Southeast Asia.