On the Dependence of Simulated Convection on Domain Size in CRMs

Abstract

We present a heuristic model to explain the suppression of deep convection in convection-resolving models (CRMs) with a small number of grid columns, such as those used in super-parameterized or multi-scale modeling framework (MMF) general circulation models (GCM) of the atmosphere. Domains with few grid columns require greater instability to sustain convection because they force a large convective fraction, driving strong compensating subsidence warming. Updraft dilution, which is stronger for reduced horizontal grid spacing, enhances this effect. Thus, suppression of deep convection in CRMs with few grid columns can be reduced by increasing grid spacing. Radiative-convective equilibrium simulations using standalone CRM simulations with the System for Atmospheric Modeling (SAM) and using GCM-coupled CRM simulations with the Energy Exascale Earth System Model (E3SM)-MMF confirm the heuristic model results.