Pacific Meridional Mode-Western North Pacific Tropical Cyclone Linkage Explained by Tropical Pacific Quasi-Decadal Variability

Previous studies argued that the Pacific Meridional Mode (PMM) impacts tropical cyclone (TC) genesis variability over the southeastern part of the western North Pacific (SE-WNP). Here, we find that the statistical relationship between PMM and SE-WNP TC genesis frequency is dominated by their co-variability on decadal timescales. The decadal component of the PMM exhibits very similar temporal and spatial features to quasi-decadal tropical Pacific sea surface temperature (SST) variability. The latter can affect SE-WNP TC activity via changes in both zonal vertical wind shear and low-level vorticity. In contrast, the interannual component of the PMM exhibits no statistically significant correlation with SE-WNP TC genesis. Furthermore, observations show that both interannual and decadal variability of SE-WNP TC activity are well correlated with the commonly used Nino3.4 El Nino-Southern Oscillation index. Thus, equatorial Pacific SST variability is the dominant source of SE-WNP TC activity predictability on different timescales.