The maximum intensity of tropical cyclones in axisymmetric numerical model simulations

An axisymmetric numerical model is used to evaluate the maximum possible intensity of tropical cyclones. As compared with traditionally formulated nonhydrostatic models, this new model has improved mass and energy conservation in saturated conditions. In comparison with the axisymmetric model developed by Rotunno and Emanuel, the new model produces weaker cyclones (by ∼10%, in terms of maximum azimuthal velocity); the difference is attributable to several approximations in the Rotunno-Emanuel model. Then, using a single specification for initial conditions (with a sea surface temperature of 26°C), the authors conduct model sensitivity tests to determine the sensitivity of maximum azimuthal velocity (υmax) to uncertain aspects of the modeling system. For fixed mixing lengths in the turbulence parameterization, a converged value of υmax is achieved for radial grid spacing of order 1 km and vertical grid spacing of order 250 m. The fall velocity of condensate (Vt) changes υmax by up to 60%, and the largest υmax occurs for pseudoadiabatic thermodynamics (i.e., for Vt > 10 m s⁻¹). The sensitivity of υmax to the ratio of surface exchange coefficients for entropy and momentum (CE/CD) matches the theoretical result, υ