Cloud-resolving models (CRMs) can be used in conjunction with observations and single-column models (SCMs) to test and improve cloud parameterizations for GCMs. GEWEX Cloud System Study (GCSS) Working Group 4 (Precipitating Convective Cloud Systems) recently completed two projects designed to evaluate CRMs and SCMs using TOGA COARE datasets. Here we describe one of these projects.
CRMs and SCMs were evaluated by testing their ability to determine the large-scale (domain and time-averaged) statistics of precipitating convective cloud systems during a multiday period. The large-scale quantities required for the simulations (initial conditions, upper and lower boundary conditions, and large-scale advective tendencies) are based on observations averaged over the Intensive Flux Array (about 500 km by 500 km). The participating models included seven 2D CRMs, one 3D CRM, and eight SCMs. The models have been evaluated by comparing the results of the simulations to observed large-scale (average) quantities.
The similarities between the results from the CRMs and the observations for tropospheric enthalpy, precipitable water, OLR, and cloud (liquid plus ice) water path, among others, confirms that the bulk characteristics of convection are determined (in a diagnostic sense) by the large-scale thermodynamic advective tendencies, and suggests that CRMs are useful tools for performing this diagnosis. Systematic differences that occurred between the SCM and CRM results for several quantities suggests that the CRM results should be useful for improving the SCMs.