Characterizing the Impact of Biases in Tropical Interbasin SST Interactions on Tropical Cyclone Frequency

The influence of tropical Pacific sea surface temperatures (SSTs) on tropical cyclone (TC) activity in the North Atlantic, and conversely, the impact of tropical North Atlantic SSTs on TC activity in the Western North Pacific, are well-documented. For example, El Niño conditions, characterized by warmer Pacific SSTs, typically reduce TC activity in the Atlantic due to increased wind shear and reduced atmospheric moisture, both of which are unfavorable for TC development. However, prevalent tropical SST biases in current climate models challenge our ability to accurately characterize the impact of interbasin SST teleconnections on TC activity. In this study, we conducted a series of historical nudging experiments using the Community Earth System Model (CESM), in which SSTs in the tropical Atlantic and Pacific were prescribed independently, with and without allowing adjacent basins to adjust to the SST corrections. By downscaling the resulting TCs using the Columbia Hazard model (CHAZ) and comparing the synthetic TCs from the perturbed experiments to the control, we quantified the impact of both local and remote SST biases on TC frequency and distribution in each basin. Our results indicate a significant impact of SST biases on TC activity in both basins, with the influence of tropical Atlantic SST biases on TC activity in the Western North Pacific being more substantial than previously recognized.