Resolution sensitivity of GRIST Nonhydrostatic Model During DYAMOND winter from 120 km to 5 km

This work investigates the resolution sensitivity of an explicit dynamics-microphysics coupled system using the GRIST nonhydrostatic model, with varying uniform horizontal resolutions (120 km, 60 km, 30 km, 15 km, 5 km). The experiments follow the DYAMOND (DYnamics of the Atmospheric general circulation Modeled On Non-hydrostatic Domains) winter protocol that covers a 40-day integration from UTC00, 20^th  to UTC00, Jan to 29^th, Feb, 2020. The five simulations did not activate parameterized convection, and no specific tuning of model physics is employed such that the direct resolution response of a fixed model system can be examined. One 120-km run with parameterized convection is done to serve as a coarse-resolution reference. Other model configurations for different runs are kept as consistent as possible except certain small differences. Results demonstrate that the model gradually improve its representation of the fine-scale features (e.g., kinetic energy spectra) as resolution increases. In terms of 40-day averaged climate, the 5-km run has an overall more realistic simulation of the rainfall distribution than lower-resolution simulations without parameterized convection (e.g., spatial distribution). Most zonally averaged climate statistics are less prone to be altered by the resolution, except those fields associated with cloud water (e.g., shortwave cloud radiative forcing). This finding was also reached by an earlier study using the ICON model. Though with better fine-scale details, the coarse-resolution averaged features of the 5-km model without parameterized convection do not necessarily (and automatically) gets better than a 120-km simulation with parameterized convection. The tropical rainfall frequency-intensity spectra become more realistic in the 5-km no-convection run, but the 120-km run with parameterized convection shows a more realistic zonally averaged mean state. This impies more development and tuning efforts are still required for global km-scale models.