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

Abstract

How 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.

The influence of the Atlantic multidecadal oscillation on the interdecadal variability of winter precipitation in the Greater Mekong Subregion

“…Fan et al . (2019) noted that warming of the North Atlantic during the positive phase of the AMO favours the eastward propagation of anomalous wave trains from the North Atlantic to East Asia, which has induced a high‐pressure anomaly and suppressed the precipitation over southern China and eastern Indochina Peninsula.…”

Impact of Atlantic multidecadal oscillation on interannual relationship between ENSO and East Asian early summer monsoon

“…Recently, Fan et al . (2019) proposed that the Atlantic multidecadal oscillation (AMO) can modulate the early and late summer precipitation anomalies associated with El Niño in Southeast Asia. During the positive phase of the AMO, the impact of El Niño on Southeast Asian precipitation in early summer is largely reduced by the negative WNP SSTAs, while the late summer precipitation in South China and the Indochina peninsula is suppressed by the anomalous wave trains propagating along the 'great circle route'.…”

“…However, Fan et al . (2019) proposed a possible mechanism affecting the precipitation anomalies associated with El Niño in the early summer and late summer based only on observations, lacking any confirmation by numerical simulations. In addition, we found that the ENSO's relationship with the East Asian early summer monsoon (EAESM) is different from that with the EASM during the whole summer season.…”

Monthly Variations of the Winter Precipitation over the Philippines During the Mature Phase of Eastern Pacific El Niño

“…In fact, the influence of Pacific SST anomalies on northeast Asia summer precipitation has been reported non-consistent during the whole summer and sometimes shows significant sub-seasonal variations (Xu et al, 2017). The El Niño-related precipitation anomalies over Southeast Asia is different between periods of early and late summer (Fan et al, 2019). Therefore, to investigate the ENSO-related winter precipitation anomaly from a monthly perspective is of great importance.…”