Convergence of Convective Updraft Ensembles With Respect to the Grid Spacing of Atmospheric Models

Atmospheric deep moist convection can organize into cloud systems, which impact the Earth's climate significantly. High-resolution simulations that correctly reproduce organized cloud systems are necessary to understand the role of deep convection in the Earth's climate system. However, there remain issues regarding convergence with respect to grid spacing. To investigate the resolution necessary for a reasonable simulation of deep convection, we conducted grid-refinement experiments using state-of-the-art atmospheric models. We found that the structure of an updraft ensemble in an organized cloud system converges at progressively smaller scales as the grid spacing is reduced. The gap between two adjacent updrafts converges to a particular distance when the grid spacing becomes as small as 1/20-1/40 of the updraft radius. We also found that the converged inter-updraft distance value is not significantly different between Reynolds-averaged Navier-Stokes simulations and large eddy simulations for grid spacings in the terra incognita range.