Abstract:Based on the monthly precipitation of 643 stations in China, NCAR/NCEP reanalysis data and NOAA ERSST sea surface temperature (SST) data from 1961 to 2023, the impacts of early and late onset of El Nino on summer precipitation in China are analyzed. The results are as follows. Westerly wind anomalies in the equatorial West-Central Pacific are more pronounced in June-August of years with early El Nino onset than in years with late El Nino onset, resulting in a more obvious warming of SST in the equatorial East-Central Pacific in earlier onset years, and the SST in this period continues to rise. However, the positive anomaly of SST in the equatorial East-Central Pacific in the later onset years of El Nino is not obvious and changes slowly. There are obvious differences in summer precipitation in central and eastern China between the El Nino earlier and the El Nino later onset years, especially in July and August. In the El Nino earlier onset years, the Western North Pacific anomalous anticyclone (WNPAC) generally appears around August, the summer precipitation in central and eastern China is distributed in the “-+-” pattern from south to north, with more precipitation than normal in Jianghuai Region, and less precipitation than normal in other areas. In June, the West Pacific has an abnormal cyclone and the precipitation in most of China’s central and eastern parts is less than normal. In July, the abnormal cyclone in the West Pacific retreats southward significantly, the precipitation in most parts of the Jiangnan, Northwest and North China continues to be less than normal. And the abnormal anticyclone to the east of Japan significantly extends westward and develops southward, which makes the southeast coastal areas of China turn to be dominated by abnormal southerly winds, leading to excessive precipitation along the southern China coast and in Jianghuai Basin. In August, the cyclone in the Northwest Pacific turns into an anomalous anticyclone and WNPAC begins to appear, so the precipitation over the middle and lower reaches of the Yangtze River and most parts of its south is more than normal, while the precipitation in most parts of northern China is less than normal. In the later onset years of El Nino, WNPAC usually appears in October or later, and the West Pacific has an abnormal cyclone from June to August. The summer precipitation in the central and eastern regions of China is distributed in the “+-+” pattern from south to north, and the precipitation anomaly persistence characteristics of each month are obvious.