A Tropical Cyclone Model Resolving Mesoscale Organized Convection with Prognostic Treatment of Subgrid-scale Cloud Water

Abstract

A new version of a tropical cyclone model is presented as an extension of Yamasaki’s (1986) model that intended to resolve mesoscale organized convection by a grid and treat the cumulus-scale motion as the subgrid-scale. Two important imporvements are made in this study. One is a prognostic treatment of cumulus-scale cloud water, which was treated diagnostically in the old version. The other is that the ratio of the cumulus-scale ascending area is not assumed to be sufficiently small compared to unity. Results from numerical experiments indicate that the features of tropical cyclones (including rainwater distribution) simulated by the new and old versions are essentially similar, but the cloud water distribution is simulated more realistically by the new version, as evident from the model formulation. Clarification of the impact of the finite area ratio and an improvement of its assumption remain to be studied.