Resolution Sensitivity of the GRIST Nonhydrostatic Model From 120 to 5 km (3.75 km) During the DYAMOND Winter

Abstract

We investigated the resolution sensitivity of the Global-to-Regional Integrated forecast SysTem global nonhydrostatic model characterized by explicit dynamics–microphysics coupling using varying uniform resolutions (120, 60, 30, 15, and 5 km). The experiments followed the DYnamics of the Atmospheric general circulation Modeled On Non-hydrostatic Domains (DYAMOND) winter protocol, which covers a 40-day integration. These simulations did not activate parameterized convection. One 120 km test with parameterized convection was performed as a coarse-resolution reference. Other model configurations for different simulations were kept as consistent as possible. Our results showed that the model gradually improved its representation of the fine-scale features as the resolution increased. The 5 km simulation was overall close to a 3.75 km simulation during the first 12 days of the DYAMOND winter. With respect to the mean climate, the 5 km simulation had a more realistic rainfall distribution than the lower resolution explicit convection simulations. Cloud water and the related physical fields (e.g., shortwave cloud radiative forcing) had a large resolution sensitivity. The tropical rainfall frequency–intensity spectra became more realistic in the 5 km explicit convection simulation, but the 120 km run with parameterized convection showed a more realistic mean climate. As the resolution increases, the mean bulk effect of finely resolved model convection gradually converges to that of parameterized convection. The mean climate of this storm-resolving model has slightly higher rainfall biases than a parameterized convection coarse-resolution model, highlighting the importance of balancing resolved- and under-resolved model convection for developing a unified multiscale global model.