Intensifying effects of El Nino events on winter precipitation extremes in southeastern China

摘要

This paper studies the impacts of El Nino-Southern Oscillation (ENSO) on wintertime extreme precipitation in China from 1961 to 2017, and possibly different influences of two El Nino types are also examined. We find that ENSO poses profound influences on extreme precipitation in many portions of China. El Nino (La Nina) intensifies (weakens) the winter precipitation extremes in southeastern China (SEC) and slightly weakens (intensifies) those in central-north China, mainly by changing the frequency rather than the intensity of extreme precipitation. Further analysis suggests that the East Asian winter monsoon tends to be weaker during El Nino winters, suppressing the southward invasion of cold dry air. Via the weakened Walker circulation, El Nino also triggers anomalously descending motion and anticyclone over the western North Pacific (WNP), which exhibits southwesterly anomalies over SEC and is thus conducive to the transport of sufficient moisture into that area. The changes over WNP are also accompanied by ascending motions over East Asia via a local meridional circulation alike the Pacific-Japan pattern. Meanwhile, El Nino induces a southward-displaced East Asian jet stream, as characterized by intensified westerly over southern China, corresponding to anomalously ascending motion there. Together, these changes facilitate the updrafts of circulations and the condensation of water vapor, thus increasing the occurrence of extreme precipitation events in SEC. Moreover, we find that different Nino types exhibit distinct subregional influences. In particular, the canonical eastern Pacific El Nino significantly increases the frequency of extreme precipitation in South China, whereas the Modoki central Pacific El Nino mainly impacts that in East China.