Performance of a New Convective Parameterization Scheme on Model Convergence in Simulations of a Tropical Cyclone at Grey-Zone Resolutions

Abstract

he latest version of the Weather Research and Forecasting model (WRFV3.5) is used to evaluate the performance of the Grell and Freitas (GF13) cumulus parameterization scheme on the model convergence in simulations of a tropical cyclone (TC) at gray-zone resolutions. The simulated TC intensity converges to a finite limit as the grid spacing varies from 7.5 to 1 km. The reasons for the model convergence are investigated from perspectives of subgrid-scale processes and thermodynamic and dynamic structures. It is found that the impacts of above factors are notably different with varying model resolutions. The convective heating and drying increase as the grid spacing decreases, which inhibits the explicit microphysical parameterization preventing the simulated TC from overly intensifying. As the grid spacing decreases from 7.5 to 5 km, the TC intensity increases because of a stronger secondary circulation, a larger magnitude and proportion of strong eyewall updraft, and a greater amount of latent heating in the eyewall. As the grid spacing decreases from 5 to 3 km, the radius of maximum wind (RMW) decreases and the radial pressure gradient increases leading to an increase in TC intensity. The simulated TC intensity changes slightly as the grid spacing decreases from 3 to 1 km since the RMW and the storm structure both change little. The slight changes in the simulated TC intensity at such high resolutions indicate a great model convergence. Therefore, the GF13 presents an appropriate option that increases the model convergence in the TC intensity simulation at gray-zone resolution.