A diagnostic study of the impact of El Nino on the precipitation in China

The impact of El Nino on the precipitation in China for different seasons a re investigated diagnostically. It is found that El Nino can influence the precipitation in China significantly during its mature phase. In the Northe rn winter, spring and autumn, the positive precipitation anomalies are foun d in the southern part of China during the EI Nino mature phase. In the Nor thern summer, the patterns of the precipitation anomalies in the El Nino ma ture phase are different from those in the other seasons. The negative prec ipitation anomalies appear in both southern and northern parts of China, wh ile in between around the lower reaches of the Yangtze River and the Huaihe River valleys the precipitation anomalies tend to be positive. In the Northern winter, spring and autumn, the physical process by which El Nino affects the precipitation in the southern part of China can be explai ned by the features of the circulation anomalies over East Asia during the El Nino mature phase (Zhang et al., 1996). The appearance of an anticycloni c anomaly to the north of the maritime continent in the lower troposphere d uring the El Nino mature phase intensifies the subtropical high in the west ern Pacific and makes it shift westward. The associated southwesterly flow is responsible for the positive precipitation anomalies in the southern par t of China. In the Northern summer, the intensified western Pacific subtrop ical high covers the southeastern periphery of China so that the precipitat ion there becomes less. In addition, the weakening of the Indian monsoon pr ovides less moisture inflow to the northern part of China.