To address these questions, we use the SAM cloud-system resolving model to simulate radiative-convective equilibrium on a rapidly rotating f-plane, subject to constant tropospheric radiative cooling. We use a homogeneous surface with fixed temperature and with surface saturation vapor pressure scaled by a factor 0-1 relative to that over pure water – allowing for continuous variation between moist and dry limits. As a second way of investigating the moist-dry transition, we also conduct simulations across a wide range of surface temperatures (between 240 K and 300 K), since very low surface temperatures decrease the surface latent heat flux to near zero and also reach a nearly-dry dynamical limit.
We find that a completely moist surface, and sea-surface temperatures above 280 K, both yield “normal” TC-world states where multiple vortices form spontaneously and persist for tens of days. A completely dry surface, or the lowest sea-surface temperature of 240 K, both also spontaneously yield similar dry TC-world states with many vortices that are even more stable and persistent. Dry cyclones are weaker and smaller than their normal moist counterparts, but have a larger radius of maximum winds compared to their outer radius, and prominent eyewall asymmetries. For both intermediate surface wetness values, and intermediate surface temperatures of 250-270 K, we find that spontaneous cyclogenesis strikingly fails to occur. Simulations with time-varying surface moisture and sea-surface temperatures are used to explore whether these constraints on spontaneous cyclogenesis also limit the survival of existing storms as ambient conditions slowly change.