On the Role of Sea Surface Temperature in the Clustering of Global Tropical Cyclone Formation

This study examines the potential impacts of large-scale atmospheric circulations that are forced by sea surface temperatures (SST) on global tropical cyclone (TC) formation. Using the Geophysical Fluid Dynamics Labora-tory (GFDL) global atmosphere and land surface model, version 4 (AM4), under different SST distributions, it is found that the east-west clustering of global TC formation is mainly governed by large-scale circulations in response to given SSTs, instead of direct ocean surface fluxes associated with zonal SST anomalies. Our zonally homogeneous SST simula-tions in the presence of realistic surface coverage show that TC clusters still emerge as a result of the breakdown of zonal circulations related to land-sea distribution, which produce specific "hotspots" for global TC formation. Sensitivity experi-ments with different climate warming scenarios and model physics confirm the persistence of these TC clusters in the absence of all zonal SST variations. These robust results offer new insights into the effects of large-scale circulation and terrain forcing on TC clusters beyond the traditional view of direct SST impacts, which are based on the direct alignment of the warmest SST regions and TC clusters. In addition, our experiments also capture internal variability of the global TC frequency, with an average fluctuation of 6-8 TCs at several dominant frequencies of ;3, 6, and 9 years, even in the absence of all SST interannual variability and ocean coupling. This finding reveals an intrinsic "noise" level of the global TC frequency that one has to take into account when examining the past and future trends in TC activity and their related significance or detectability.SIGNIFICANCE STATEMENT: In this study, the clustering of global tropical cyclone (TC) formation is investi-gated, using global simulations under different idealized sea surface temperature (SST) distributions. Our results show that it is the response of the large-scale tropical circulations to SST anomalies that is mostly responsible for the cluster-ing of global TC formation rather than surface flux differences. It is also found that the tropical atmosphere contains inherent fluctuations in the global TC frequency of 6-8 TCs every 3-9 years, even in the absence of all SST interannual and zonal variability. These results offer new insight into the role of tropical dynamics in governing TC climatology and suggest possible mechanisms underlying the clustering of global TC formation under different climate conditions.