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 are investigated diagnostically. It is found that El Nino can influence the precipitation in China significantly during its mature phase. In the Northern winter, spring and autumn, the positive precipitation anomalies are found in the southern part of China during the EI Nino mature phase. In the Northern summer, the patterns of the precipitation anomalies in the El Nino mature phase are different from those in the other seasons. The negative precipitation anomalies appear in both southern and northern parts of China, while 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 explained by the features of the circulation anomalies over East Asia during the El Nino mature phase (Zhang et al., 1996). The appearance of an anticyclonic anomaly to the north of the maritime continent in the lower troposphere during the El Nino mature phase intensifies the subtropical high in the western Pacific and makes it shift westward. The associated southwesterly flow is responsible for the positive precipitation anomalies in the southern part of China. In the Northern summer, the intensified western Pacific subtropical high covers the southeastern periphery of China so that the precipitation there becomes less. In addition, the weakening of the Indian monsoon provides less moisture inflow to the northern part of China.