Responses of tropical easterly jet to different global warming patterns and implications for future tropical cyclone activity

The tropical easterly jet (TEJ) is a key upper-tropospheric circulation feature that influences regional climate and tropical cyclone (TC) activity. This study examines how the TEJ responds to distinct global warming patterns and the implications for future TC activity using high-resolution simulations from the HIRAM-C180 atmospheric general circulation model. We find that La Niña-like warming strengthens the TEJ over the western Pacific but weakens it over the Indian Ocean, whereas El Niño-like warming weakens the TEJ in both regions. These contrasting responses are linked to pattern-dependent changes in the Walker circulation and associated convection heating patterns. Basin-separation experiments under El Niño-like warming further reveal that Indian Ocean warming exerts dominant control over the western Pacific TEJ, Pacific Ocean warming has the strongest influence on the Indian Ocean TEJ, and Atlantic SST anomalies modulate both jets through cross-basin teleconnections. A weakened Indian Ocean TEJ reduces easterly vertical wind shear, creating a more favorable environment for TC activity in the northern Indian Ocean during the transition seasons, and supporting more frequent intense storms. Over the western North Pacific, a weakened western Pacific TEJ under El Niño-like warming suppresses TC activity by weakening upper-level divergence, whereas La Niña-like warming strengthens the TEJ and promotes TC formation. These findings emphasize that the spatial structure of sea surface temperature change, and the relative roles of individual ocean basins, must be accounted for in reliable projections of regional atmospheric circulation and future TC risk.