Parameter study of tropical cyclones in rotating radiative-convective equilibrium with meso-scale resolution

Rotating radiative-convective equilibrium is studied by extracting the column physics of a meso-scale resolution global atmospheric model that simulates realistic hurricane frequency statistics and coupling it to rotating hydrostatic dynamics in doubly-periodic domains. The results help in understanding the tropical cyclones simulated in the global model. The parameter sensitivities also provide a reference point for analogous future studies with cloud resolving models.

The authors first examine the parameter sensitivity of the equilibrium achieved in a large square domain (2x10⁴ km on a side) to sea surface temperature, ambient rotation rate and surface drag coefficient. In such a large domain, multiple tropical cyclones exist simultaneously. The number, size and intensity of these tropical cyclones are investigated. Two model parameters, one in the convection closure scheme and one related to sub-grid scale horizontal mixing in the dynamical core, are also perturbed, and the behavior in this idealized configuration is broadly consistent with that in the global model.

The variation of rotating radiative-convective equilibrium with domain size is also studied. As domain size increases, the equilibrium evolves through four regimes: a single tropical depression, an intermittent storm with intensity varying widely over a cycle, a single sustained storm, and finally multiple storms. The sustained storm regime shifts towards larger domain size as SST increases or f decreases.