Impact of Spring and Summer Onset Type ENSO on Summer Precipitation in China

The NCEP reanalysis data, SST data, and precipitation measured at 617 weather stations across China have been exploited to investigate influences of spring and summer onset types of ENSO events on the summertime precipitation in China. El Niño and La Niña events can be classified into two major types: The spring type ENSO events whose onset time is from April to June (hereafter ELSP1, ELSP2, ELSP3, and LASP) and the summer type ENSO events whose onset time is from July to October (hereafter ELSU and LASU). During the summer of ELSP1 years, consistent negative precipitation anomalies are found in China. Large negative precipitation anomalies are particularly distinct in the Yellow River basin. In the summer of the following year, precipitation anomalies demonstrate a "－, ＋, －" meridional pattern from south to north. Precipitation anomalies are opposite in the summer of ELSP2 years and that of the following years, that is more precipitation occur in the summer of ELSP2 years and less precipitation occur in the summer of the following years. During the ELSP3 summers, less precipitation occur in South China, whereas more precipitation occur in other regions of China. In the summer of the following years, however, positive precipitation anomalies are concentrated in the Yangtze River valley and North China. In the summer of ELSU years, negative precipitation anomalies appear to the north of the Yangtze River while positive anomalies occur in Southwest China and coastal region of South China. In the summer of the following years, precipitation anomalies demonstrate a "－, ＋, －, ＋" meridional pattern from south to north. Different to precipitation anomalies corresponding to other spring type of El Niño events, less rain occur in the summer of the spring type of La Niña (LASP) years and more rain occur in the summer of the following years. In the summer of LASP years, less precipitation occur in southern Yangtze River basin while more precipitation occur in northern Yangtze River basin. In contrast, negative precipitation anomalies are found over most area of China except the middle and lower reaches of the Yangtze River areas, where precipitation is slightly higher than normal. These changes in precipitation are closely related to anomalies in ascending and descending branches of the Hadley circulation and water vapor transport caused by the different onset types of ENSO events. It is worth noting that the anomalous circulations induced by the summer type of La Niña events only present weak implications for the forecast of summer precipitation in China.