The Impact of the Pattern of Surface Warming on Tropical Cyclone Activity in HighResMIP

Tropical cyclone (TC) activity is modulated by surface boundary conditions like sea surface temperature (SST). It is expected that changes in SST impact TC activity at both regional and global scales. However, the evolution of this impact in a warmer climate remains uncertain. Changes in the pattern and distribution of surface warming could produce different weather and climate outcomes, especially for extreme weather events like TCs. In this project, the CMIP6 HighResMIP simulations are used to examine the impact of the pattern of surface warming on TC activity. TC tracks in each model run using the TRACKS and Tempest Extremes algorithms are obtained from the CEDA Data Archive. In the eastern tropical and subtropical Pacific Ocean, observed sea surface temperatures (SSTs) have cooled by approximately 0.4 K per decade from 1979 to 2014. These observed SSTs are used as the boundary condition for the uncoupled, atmosphere-only HighResMIP simulations covering 1950-2014 (highresSST-present). The coupled atmosphere-ocean simulations covering 1950-2014 (hist-1950) do not show this observed cooling trend, instead showing near uniform warming across the tropics and subtropics. We hypothesize that the observed cooling trends in the eastern tropical and subtropical Pacific Ocean will contribute to less TCs in the Eastern North Pacific Basin within the uncoupled, atmosphere-only simulations compared to the coupled atmosphere-ocean simulation. We also consider the trends in TC activity globally. We compare the trends over the last 40 years of the historical period (1975-2014) and the full historical period (1950-2014).