Tropical cyclones (TC) are among the most destructive natural hazards worldwide,producing devastating winds,torrential rainfall,and storm surges.Under global warming,understanding long-term changes in TC activity and the underlying physical mechanisms is essential for improving prediction and mitigating associated risks.This study investigates two major TC genesis regions——the western North Pacific (WP) and the eastern North Pacific (EP) using observational and reanalysis datasets spanning 1950—2023.We examine changes in TC genesis frequency and latitude,along with the dominant environmental factors modulating these changes.
The leading EOF (Empirical Orthogonal Function) mode of global SST (sea surface temperature) is used to derive the principal component time series (PC1),representing the long-term global warming signal.Correlation analyses reveal a significant positive relationship between EP TC genesis frequency and PC1,indicating enhanced TC activity in the EP under warming.In contrast,the correlation between WP and PC1 is negative but not statistically significant.The mean latitude of TC genesis exhibits a significant northward shift over the WP but a significant southward shift over the EP,both closely linked to PC1.
Neither the genesis potential index (GPI) nor the dynamical genesis potential index (DGPI) effectively captures these observed long-term changes,suggesting limitations in traditional metrics under a warming climate.Further diagnostic analyses show that environmental zonal vertical wind shear plays a pivotal role in producing the contrasting TC frequency trends.Increasing westerly shear over the WP suppresses disturbance amplification and reduces TC formation,whereas increasing easterly shear over the EP enhances the growth of precursor disturbances and increases TC frequency.Moreover,basin-specific meridional gradients in atmospheric stability and vertical wind shear largely determine the direction and magnitude of TC genesis latitude shifts.Over the WP,stronger stability increases to the south,and reduced shear to the north favors a northward migration of genesis locations.Over the EP,a greater increase in atmospheric stability to the north leads to a southward shift.
A linear regression model based on zonal wind shear successfully reproduces the observed trends in TC genesis frequency in both basins.Similarly,a multivariate regression model incorporating atmospheric stability and vertical wind shear captures the observed shifts in TC genesis latitude,lending further support to the proposed mechanisms.Overall,the results highlight the central role of large-scale environmental shear and stability in shaping basin-dependent TC responses to global warming.