Comparison of Convective Aggregation as Simulated by Two Different Cloud Resolving Models

Convective aggregation, as simulated by cloud-resolving models, is believed to be relevant to the effects of convection on the climate system. In a simulation of radiative-convective equilibrium using the System for Atmospheric Modeling (SAM), with periodic boundary conditions, Alexandra Naegele found that the clouds organized into “aggregations.” She also found that the aggregated cloud system pulsated with a period of ten simulated hours. The overall character of her results was robust with respect to changes in the model’s
configuration, including a major change to the microphysics parameterization. We attempted to reproduce the SAM results with the Regional Atmospheric Modeling System (RAMS). We matched the domain size, grid spacing, and initial conditions for RAMS with those used in SAM, but the models do differ in numerous ways including their numerical schemes, and their parameterizations of microphysics, turbulence, and radiation. Our results show that RAMS does simulate aggregated convection, but not as strongly as SAM, and without any sign of pulsations. We will present an analysis of the reasons for these differences between the two sets of model results.