Two Opposite Extreme Events in Seasonal Mean Winter Rainfall over East China during the Past Three Decades

Abstract

In this study, the extremes of winter seasonal mean precipitation have been investigated by using daily precipitation data from 91 stations in East China, the Na- tional Centers for Environmental Prediction/the National Center for Atmospheric Research (NCEP/NCAR) month- ly reanalysis, and sea surface temperature data from the Hadley Centre for 1979-2007. The largest anomalous rainfall amount was observed in regions south of the Yangtze River. In the most recent three decades, extreme events in the seasonal mean winter precipitation occurred in 1985 and 1997. Because it was influenced mainly by a La Nina event, the precipitation in 1985 showed a deficit following a stronger winter monsoon. The rainfall amount in 1997 was influenced by El Nino and was significantly larger than normal with a weaker winter monsoon. Both the circulation anomalies and wave energy dispersions during the winters of 1985 and 1997 differed significantly. In 1985, the North Atlantic Oscillation anomalously ex- cited the Eurasian-Pacific teleconnection and circum- global teleconnection phenomena. Consequently, Rossby wave energy propagated along the north and south branches of the westerlies, strengthening the East Asian trough along with a stronger winter monsoon, which fa- cilitated the wintertime dry extreme in East China. In 1997, however, Rossby wave energy propagated from low latitudes northeastward into the southern part of China, resulting in a weaker winter monsoon and the wettest winter. The results of this study will be helpful for future monitoring and prediction of extreme winter rainfall events in East China.