Decadal Anomalies of Winter Precipitation over Southern China in Association with El Niño and La Niña

Using multiple datasets, this paper analyzes the characteristics of winter precipitation over southern China and its association with warm and cold phases of El Nio-Southern Oscillation during 1948-2011. The study proves that El Niño is an important external forcing factor resulting in above-normal winter precipitation in southern China. The study also reveals that the impact of La Niña on the winter precipitation in southern China has a decadal variability. During the winter of La Niña before 1980, the East Asian winter monsoon is stronger than normal with a deeper trough over East Asia, and the western Pacific subtropical high weakens with its high ridge retreating more eastward. Therefore, anomalous northerly winds dominate over southern China, leading to a cold and dry winter. During La Niña winter after 1980, however, the East Asian trough is weaker than normal, unfavorable for the southward invasion of the winter monsoon. The India-Burma trough is intensified, and the anomalous low-level cyclone excited by La Niña is located to the west of the Philippines. Therefore, anomalous easterly winds prevail over southern China, which increases moisture flux from the tropical oceans to southern China. Meanwhile, La Niña after 1980 may lead to an enhanced and more northward subtropical westerly jet over East Asia in winter. Since southern China is rightly located on the right side of the jet entrance region, anomalous ascending motion dominates there through the secondary vertical circulation, favoring more winter precipitation in southern China. Therefore, a cold and wet winter, sometimes with snowy and icy weathers, would occur in southern China during La Niña winter after 1980. Further analyses indicate that the change in the spatial distribution of sea surface temperature anomaly during the La Niña mature phase, as well as the decadal variation of the Northern Hemisphere atmospheric circulation, would be the important reasons for the decadal variability of the La Niña impact on the atmospheric circulation in East Asia and winter precipitation over southern China after 1980.