Development of a Nonhydrostatic Version of the Mesoscale-Convection-Resolving Model and its Application to the Eyewall and Spiral Rainbands of Tropical Cyclones

抄録

A numerical model in which the effects of cumulus convection are incorporated as the subgrid-scale and mesoscale organized convection is resolved by the grid (mesoscale-convection-resolving model, MCRM) was developed in the 1980s with an intention of improving the parameterization schemes for moist convection, which had been used since the 1960s. As in many numerical models with parameterization in the 1980s, hydrostatic equilibrium was assumed. The present paper describes a nonhydrostatic version of the MCRM, with some modifications of the subgrid-scale effect formulation used in the hydrostatic MCRM.
Numerical experiments are performed to get some evaluation of the performance of the nonhydrostatic version of the MCRM through the comparison of the results in two cases with and without the effects of the subgrid-scale cumulus convection. Although the most efficient horizontal grid size of the MCRM ranges from about 20 km to 5 km, only the results of a 15-km grid case are presented in this paper. The initial condition used in the numerical experiments is idealized (simplified). However, such numerical experiments can be considered useful to understand the behavior of spiral rainbands and eyewall convection in well-developed tropical cyclones and to evaluate the model validity. The subgrid-scale effects in the nonhydrostatic MCRM are not so important as those in the hydrostatic MCRM. However, it is shown that the eyewall and spiral rainbands are not simulated well unless the subgrid-scale effects are incorporated.