Pacific Decadal Oscillation Modulates the Relationship Between Pacific Meridional Mode and Tropical Cyclone Genesis in the Western North Pacific

Abstract

Pacific Meridional Mode (PMM) is known to be significantly correlated with tropical cyclone (TC) genesis over the western North Pacific (WNP), while the stability of their relationship remains unknown. Here we found that their relationship is nonstationary, which depends on the phase of Pacific Decadal Oscillation (PDO). During the PDO warm phases, the PMM-emanated cyclonic circulation and ascending motion can propagate to the entire WNP due to the enhanced background convection. In contrast, during the PDO cold phases, the PMM-resulted cyclonic circulation and ascending motion are confined to the eastern WNP, while the compensated descending motion prevails in the western WNP. Accordingly, the PMM-induced consistent (inconsistent) changes in large-scale conditions across the western and eastern WNP act to strengthen (weaken) the relationship between the PMM and WNP TC genesis during the PDO warm (cold) phases. The result provides further guidance for improving seasonal prediction of TC genesis.