Sensitivity of tropical cyclone formation rate to surface warming in idealized numerical simulations

There is currently no theory for the rate of tropical cyclone (TC) formation given a particular climate, and so our understanding of the relationship between TC frequency and large-scale environmental factors is largely empirical. Here, we explore the sensitivity of TC formation rate to sea surface temperature (SST) in a series of highly-idealized cloud-permitting simulations, in which TCs evolve from a base state of rest on an f-plane. The simulations reveal a non-monotonic relationship between the time it takes for TCs to form and the prescribed SST, with moderately long spin-up times at both ends of the SST spectrum tested (292 K and 304 K), and a relatively fast evolution to genesis at the middle value of SST (298 K). Genesis potential indices diagnosed from the simulations reveal a different response to surface warming: either a monotonic increase (consistent with projections from global climate models) or relatively little change if the saturation deficit is used in place of relative humidity. The maximum intensification rate increases with warming and scales linearly with the potential intensity. Preliminary results suggest that the formation of extensive cold pools may aid in accelerating convective organization. Implications for TC frequency projections in global climate models will also be discussed.