Tropical Cyclone Potential Size

Abstract

Abstract A model for tropical cyclone (TC) potential size (PS), which is capable of predicting the equilibrium outer radius of a TC solely from environmental parameters, is proposed. The model combines an updated Carnot cycle model with a physical model for the wind profile, which serve as energetic and dynamic constraints, respectively, on the minimum pressure. Physically, the Carnot cycle model defines how much the surface pressure can be dropped energetically, and the wind profile model defines how large the steady-state storm needs to be to yield that pressure drop for a given maximum wind speed. The model yields an intrinsic length scale VCarnot/f, with f the Coriolis parameter, VCarnot similar to the potential intensity Vp, but without a dependence on the surface exchange coefficients of enthalpy Ck and momentum Cd. Analytic tests with the theory varying outflow temperature, sea surface temperature (SST), and f demonstrate that the model predictions are qualitatively consistent with the Vp/f scaling for outer size found in past work. The model also predicts a weak dependence of outer size on Cd, Ck, and horizontal mixing length lh of turbulence, consistent with numerical simulation results. Idealized numerical simulation experiments with varied tropopause temperature, SST, f, Cd, Ck, and lh show that the model performs well in predicting the simulated outer radius. The VCarnot/f scaling also better captures the dependence of simulated TC size on SST than Vp/f. Overall, the model appears to capture the essential physics that determine equilibrium TC size on the f plane.