Impacts of Eastern Pattern El Niño on The Summer Precipitation of Eastern China Through Atmospheric Circulation Anomalies

The summer precipitation in post-El Niño years (referring to years after SST anomalies reach a maximum) and the corresponding atmospheric circulation before and after the mid-1970s were investigated using the empirical orthogonal function (EOF method. The monthly summer precipitation in eastern China between 1961 and 2016 is used in this study, and the differences in summer precipitation in post-El Niño years before and after the mid-1970s were investigated. The results showed that there were statistically significant differences in summer precipitation over eastern China in post-El Niño years before and after the mid-1970s. Spatially, northern China and the region of the Jiang-Huai River show the most prominent changes; summer precipitation in North China decreased significantly before 1980, while summer precipitation in the region of the Jiang-Huai River increased remarkably. On the circulation field of zonal wind at the 300 hPa level, compared to the years before 1980, the East Asian Subtropical Westerly Jet Stream (EAWJ) accelerated at latitudes between 30°N and 40°N, with two anomalous acceleration centers on the east coast of China and west of the Tibetan Plateau. The EAWJ slows down between latitudes of 40°N and 50°N, with two anomalous deceleration centers in the northern region of Xinjiang Province and the Okhotsk Sea. The secondary circulation response excited by the two anomalous centers on the east side of EAWJ strengthens the positive vorticity anomaly in the region of the Jiang-Huai River and strengthens the negative vorticity anomaly in northern China, respectively. Elsewhere, the anomalous acceleration center over the western Tibetan Plateau causes the updraft of the southwest monsoon in a southerly direction, and water vapor transportation becomes weaker, cooperating with the weakened Eastern Asia summer monsoon and resulting in a lower vapor flux anomaly in northern China, but with more water vapor flux convergence in the Jiang-Huai area. A weakening of the dynamic lift and water vapor transport are conducive to reducing precipitation to a certain extent. However, in the region of the Jiang-Huai River, strengthened dynamic lift and water vapor flux convergences are beneficial for increasing rainfall.