Effects of the Horizontal Scales of the Cloud-Resolving Model on Tropical Cyclones in a Multiscale Modeling Framework

In this presentation, the Superparameterized Community Atmosphere Model (SPCAM) is used in a hindcast approach to simulate tropical cyclones (TCs). Three hindcast experiments are conducted, employing sub-grid cloud-resolving models (CRMs) with horizontal scales of 32 km (D32), 128 km (D128), and 1024 km (D1024). The findings indicate that D1024 produces comparable TC numbers with reanalysis data, showing 3.42 TCs per 10 days, while D32, D128, and D1024 exhibit 8.07, 4.88, and 3.73 TCs, respectively. The bias of overestimating TC numbers increases with decreasing CRM scale, with D32 producing stronger TCs with higher precipitation rates, and wind speeds. This bias is closely linked to the efficiency of adjusting convective instability in CRMs. D32 exhibits higher column-integrated water vapor under warm conditions compared to D1024, indicating inefficiency in water vapor removal due to weaker convective mass fluxes in the smaller CRM scale. The vertical transport of convection in a smaller horizontal scale will be restricted by stronger subsidence because CRM columns for compensating are limited. The distribution of accumulated convective instability is broader and more frequent in D32. As a result, large-scale precipitating systems tend to develop in D32, leading to a higher probability of TC genesis. Idealized rotating radiative-convective equilibrium experiments provide additional insights into the interaction between convection and environment under different CRM configurations.