Modulation of Pacific Decadal Oscillation on the relationship of El Niño with southern China rainfall during early boreal winter

Abstract

AbstractThe modulation of Pacific Decadal Oscillation (PDO) on the relationship of El Niño with southern China rainfall during early boreal winter (November–December) is investigated in this study. When El Niño occurs in positive phase of PDO, significantly positive rainfall anomalies only appears over the southwestern part of southern China. When El Niño occurs in negative phase of PDO, pronounced positive rainfall anomalies are observed over almost the whole southern China. Further analyses revealed that the anomalous Philippine Sea anticyclone (PSAC) and local meridional circulation play an important role in modulating the relationship of El Niño with southern China rainfall by PDO. During the negative PDO phase, under the combined influence of tropical Pacific and Indian Ocean dipole sea surface temperature anomalies pattern, the anomalous PSAC over the western North Pacific and rising motion associated with local meridional circulation over southern China provide sufficient water vapor and dynamical conditions for the formation of rainfall. During positive PDO phase, however, PSAC and local meridional circulation are only influenced by tropical Pacific and they become weak, not favoring the formation of southern China rainfall.