Variations in tropical cyclone frequency response to solar and CO2 forcing in aquaplanet simulations

Abstract

The response of global tropical cyclone (TC) frequency to solar and carbon dioxide radiative forcing is examined in TC-permitting aquaplanet general circulation model simulations. With an energetically consistent slab ocean lower boundary condition, the simulations show a larger response to positive radiative forcing from increased carbon dioxide than a solar constant increase with a comparable global-mean radiative forcing. Prescribed sea surface temperature (SST) simulations reveal that both the direct response to radiative forcing (radiative forcing with unchanged SST) and the patterned-SST response vary between forcing agents. The forcing-agent dependence of the patterned-SST response of TC frequency can be accounted for by the variation in simulated intertropical convergence zone shifts. The forcing-agent dependence of the direct response of TC frequency to radiative forcing can be accounted for by the variation in direct circulation changes and in normalized moist static energy deficit changes. That the direct TC response differs across forcing agents suggests that solar radiation manipulation geoengineering schemes will not return TC frequency to that of an unperturbed climate.