Unusual Rainfall in Southern China in Decaying August during Extreme El Niño 2015/16: Role of the Western Indian Ocean and North Tropical Atlantic SST

Abstract

Previous research has suggested that the anomalous western North Pacific anticyclone (WNPAC) can generally persist from an El Niño mature winter to the subsequent summer, influencing southern China precipitation significantly, where southern China includes the Yangtze River valley and South China. Since the late 1970s, three extreme El Niño events have been recorded: 1982/83, 1997/98, and 2015/16. There was a sharp contrast in the change in southern China rainfall and corresponding atmospheric circulations in the decaying August between the 2015/16 extreme El Niño event and the earlier two extreme El Niño events. Enhanced rainfall in the middle and upper reaches of the Yangtze River and suppressed rainfall over South China resulted from basinwide warming in the tropical Indian Ocean induced by the extreme El Niño in August 1983 and 1998, which was consistent with previous studies. However, an anomalous western North Pacific cyclone emerged in August 2016 and then caused positive rainfall anomalies over South China and negative rainfall anomalies from the Yangtze River to the middle and lower reaches of the Yellow River. Without considering the effect of the long-term global warming trend, in August 2016 the negative SST anomalies over the western Indian Ocean and cooling in the north tropical Atlantic contributed to the anomalous western North Pacific cyclone and a rainfall anomaly pattern with opposite anomalies in South China and the Yangtze River region. Numerical experiments with the CAM5 model are conducted to confirm that cooler SST in the western Indian Ocean contributed more than cooler SST in the north tropical Atlantic to the anomalous western North Pacific cyclone and anomalous South China rainfall.