Pacific Meridional Mode as a Bridge in Linking North Atlantic Oscillation and Interdecadal Variability in Tropical Cyclone Genesis in the Western North Pacific

Notable interdecadal variability in tropical cyclone (TC) genesis frequency within western North Pacific (WNP) has been well documented, yet its physical mechanisms remain unclear. This study demonstrates that the interdecadal variation in the WNP TC genesis frequency during the peak TC season (July–October) is strongly influenced to the boreal winter–spring (January–May) North Atlantic Oscillation (NAO) on interdecadal time scales, with the Pacific meridional mode (PMM) acting as a crucial intermediary. Specifically, the NAO triggers a Eurasian wave train, resulting in positive temperature anomalies over northeastern Asia. These anomalies are subsequently transported to the Kuroshio Extension region by the midlatitude westerlies, which weakens the meridional temperature gradient and reduces the strength of the subtropical westerly jet. As the jet weakens, it induces anomalous negative vorticity and anticyclonic circulation to its north. The anomalous northerly winds east of the anticyclone transport cold and dry air southward to the southeastern side of the anomalous anticyclone, where the air accumulates and sinks. This subsidence then alters the local meridional circulation, promoting anomalous deep convection over the central tropical Pacific. The enhanced tropical convection further excites a northward-propagating Pacific–North American (PNA) wave train, leading to the development of an anomalous low pressure system over the North Pacific. Anomalous westerly winds on the southeastern flank of this system subsequently amplify the PMM through wind–evaporation–sea surface temperature (SST) feedback. The PMM-related SST anomalies ultimately induce anomalous cyclonic circulation over WNP through the Gill response, creating favorable conditions for TC genesis. This result reveals a novel remote subtropical modulator of interdecadal variability in WNP TC genesis, offering valuable insights for improving TC activity predictions.