Cloud Resolving Simulation of Subtropical Low Clouds and Comparison with Cloud Object Data from CERES

This study evaluates the ability of a cloud-resolving model (CRM) to simulate the physical properties of subtropical boundary-layer cloud objects identified from Clouds and the Earth's Radiant Energy System (CERES) satellite data. A boundary-layer cloud object is defined as a contiguous region of the earth with clouds that have heights less than 3 km. The shape and size of the cloud objects are determined from satellite data and cloud-object selection criteria. The University of California-Los Angeles (UCLA)/Langley Research Center (LaRC) CRM is used in this study. A third-order turbulence closure is used in the model to parameterize the subgrid-scale condensation and turbulence associated with the unresolved boundary-layer clouds. The horizontal grid spacing used for the CRM is 1 km with domain size of 300 km; the vertical grid spacing is 40 m with a domain extending from the surface to 4 km. Probability distributions of cloud top temperature, outgoing longwave radiative flux, albedo, and cloud optical depth, etc., from CERES observations are compared with those from simulations. A general agreement in the overall shapes of all cloud physical properties between the observed and modeled distributions can be found, but each simulated cloud physical property exhibits some degree of disagreement with that observed and the reasons for these disagreements are investigated.