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Abstract:
Contribution of remote and local SST anomaly forcing during El Niño in shaping the interannual variations of precipitation over the Maritime Continent (MC) during July–October (JASO) and January–April (JFMA) seasons is investigated using an atmospheric general circulation model (AGCM). Two idealized AGCM experiments are designed to isolate the effect of anomalous SST forcing from the tropical central–eastern Pacific (CEP) and western Pacific (WP). In the first (second) experiment, climatological SST field is imposed in the tropical CEP (tropical WP) region, while observed SST is used elsewhere. The two experiments are integrated from 1 March 1982 to 29 February 2012 and are compared with a control run where observed SST is used over global ocean. Our numerical experiments indicate that, in the JASO season, the precipitation reduction prominent over the southern hemisphere (SH) side of MC is explained as a remote influence of El Niño. Positive SST anomalies over the tropical CEP associated with El Niño generate westerly wind anomalies over the tropical WP around 120°–160°E, 5°S–5°N. The anomalous westerly wind advects dry air into the SH side of MC and thus suppresses precipitation there. In the JFMA season, the reduced precipitation mainly occurring over the northern hemisphere (NH) side of MC is largely induced by the anomalous local SST forcing. The local surface ocean forcing promotes the generation of the Philippine Sea anticyclonic anomalies in the NH region. The anomalous northeasterly wind component of the anomalous anticyclone transfers dry air into the NH side of MC and reduces local precipitation.
