Spatial Scale of Convective Aggregation in Idealized Cloud-Resolving Simulations of Radiative-convective Equilibrium

A three-dimensional cloud-resolving model (CRM) is used to investigate the preferred separation distance between neighboring humid, rainy regions formed by convective aggregation in radiative-convective equilibrium without rotation. We performed simulations of convective aggregation with doubly-periodic square domains of widths 768 km, 1536 km and 3072 km. The simulation with the smallest domain size was run first. Then, the simulations in the larger domains are initialized using multiple copies of the equilibrated results in the smallest domain, plus a small perturbation. With all three domain sizes, the simulations eventually evolve to a single statistically steady convective cluster surrounded by a broader region of dry, subsiding air. We analyze the mechanisms that cause the initial multiple clusters in the larger domains to reorganize into a single cluster. In addition, for each domain size, we composite the vertical velocity, water vapor mixing ratio, and radiative cooling rate in the dry environmental region as functions of distance away from the single equilibrated cluster. We also explore the dependence of the results on the prescribed sea-surface temperature. An idealized model of steady-state convective aggregation is used to interpret the numerical results.