The Different Configurations of the East Asian Polar Front Jet and Subtropical Jet and the Associated Rainfall Anomalies over Eastern China in Summer

Abstract

Abstract To investigate the concurrent impacts of the East Asian polar front jet (EAPJ) and subtropical jet (EASJ) on the summer rainfall over eastern China, positive (strengthened EAPJ with weakened EASJ) and negative (weakened EAPJ with strengthened EASJ) configurations are identified. In the positive configuration, rainfall decreases in the northern part of eastern China and increases in the southern part, vice versa in the negative configuration. The possible mechanisms maintaining the two jet configurations are further proposed from the perspectives of sea surface temperature (SST) and synoptic-scale transient eddy activities (STEA). In the positive configuration, meridional distributed cold–warm SST anomalies over the eastern North Pacific may induce regional circulation and meridional temperature gradient anomalies, which can strengthen the EAPJ and weaken the EASJ. The central Pacific La Niña–like SST anomalies are related with the Arctic vortexlike anomalies in the stratosphere, which may strengthen the EAPJ. Furthermore, the divergence of Eliassen–Palm vectors and the conversion from eddy kinetic energy to mean kinetic energy over the active region of the EAPJ may strengthen the EAPJ, vice versa for the weakened EASJ. In the negative configuration, associated with the warm SST anomalies over the western North Pacific, the enhanced convective activities may lead to a strengthened EASJ via meridional teleconnection. The teleconnection may be intensified by the strengthened easterly vertical shear. Additionally, eastern Pacific La Niña–like SST anomalies may intensify the Walker circulation, which may strengthen the EASJ via the Hadley circulation. The STEA-related anomalies are almost opposite those in the positive configuration, especially for the weakened EAPJ.