Recent Changes in ENSO Teleconnection over the Western Pacific Impacts the Eastern China Precipitation Dipole

Abstract

he eastern China precipitation dipole (ECPD) features an out-of-phase relationship between boreal summer precipitation over the middle and lower reaches of the Yangtze River and the Hetao region to its northwest. The precipitation dipole is strongly influenced by ENSO teleconnections over the western tropical Pacific. Here it is shown that a pronounced weakening of both the rainfall variability over eastern China as well as the precipitation dipole structure occurred around the mid-1990s. The changes have been analyzed by considering two epochs: one during 1979?95 and the other during 1996?2009. The characteristic feature of the circulation anomaly during the first epoch is the well-known East Asia?Pacific/Pacific?Japan (EAP/PJ) pattern, a quasi-meridional teleconnection pattern emanating from the western tropical Pacific. On the other hand, during the latter epoch eastern China precipitation variability occurs as an integral part of the circulation anomalies over the western Pacific. In contrast to the more meridionally restricted anomalies during canonical ENSO episodes, the western Pacific circulation has a significantly larger meridional scale. Intriguingly correlation of the precipitation dipole with Pacific sea surface temperature flips in sign during the second epoch, with enhanced precipitation over southeastern China associated with La Niña?like variability, in contrast to the co-occurrence of enhanced precipitation over this region with El Niño during the first epoch. The results suggest that the dominance of Modoki or central Pacific El Niños, and the altered structure of ENSO teleconnections associated with these, may play a role in the weakened ECPD structure during the latter epoch.