Rotating radiative‐convective equilibrium simulated by a cloud‐resolving model

Abstract

The results of a series of cloud‐resolving radiative‐convective equilibrium (RCE) simulations are presented. The RCE simulations, used as an idealization for the mean tropical climate, are run for a wide range of prescribed sea‐surface temperatures (SSTs), from 21 o C to 36 o C, representing the range of past, present, and, possibly, future mean tropical SSTs. The RCE with constant Coriolis parameter f is contrasted with nonrotating RCE. The Coriolis parameter is artificially increased from typical values in the Tropics by about one order of magnitude to allow multiple tropical cyclones (TCs) to coexist in a relatively small 2300 × 2300 km 2 domain with a 3 km horizontal grid spacing. Nonrotating RCE is also simulated, but using a substantially smaller, 384 × 384 km 2 domain. Rotating RCE, which we nickname “TC World,” contains from 8 to 26 TCs with the average number of TCs monotonically decreasing with increasing SST. At the same time, the TCs' size, intensity, and per‐TC precipitation rate tend to increase in response to increasing SST. For example, the average per‐TC kinetic energy and precipitation rate tend to double for every 6 o C SST increase. These results are consistent with scaling laws in which TC velocities and inner core diameters scale with the potential intensity and its ratio to the Coriolis parameter, respectively, while the separation between cyclone centers appears to scale with the deformation radius. It is also found that the outflow temperature of TC's, as defined as the height of the local maximum of the upper‐troposphere cloud fraction, remains relatively invariant with SST. The cold‐point tropopause height in TC World is found to be about 2 km higher than the corresponding height in nonrotating RCE. The number of tropical cyclones decreases as sea‐surface temperature increases The size and intensity of tropical cyclones increase with increasing SST The outflow temperature of TCs stays approximately constant