2. RACORO-FASTER: large-eddy simulations

Description

New case studies are being constructed in the FAst-physics System TEstbed and Research (FASTER) project, based on continental boundary-layer-cloud observation during the Routine AAF Clouds with Low Optical Water Depths (CLOWD) Optical Radiative Observations (RACORO) field campaign. This poster presents preliminary results from large-eddy simulations (LESs) for the three 60-hour case study periods (See Vogelmann et al. for the detail of the case generation and Lin et al. for single-column model [SCM] simulations). The initial runs are performed by the GISS Distributed Hydrodynamic Aerosol and Radiative Modeling Application (DHARMA) model and the Weather Research and Forecasting (WRF) model implemented with forcing ingestion and other functions for flexible LES (WRF-FASTER). The two LES models commonly capture the significant transitions of cloud-topped boundary layers in the three periods: daytime breakup of stratus and stratocumulus clouds, diurnal evolution of cumulus layers repeating over multiple days, and nighttime evolution/daytime diminution of thick stratus. Aircraft observations are then used to statistically evaluate predicted cloud droplet number concentrations under varying aerosol and cloud conditions. Sensitivity tests are presented that allow us to refine the model configuration for the combined use of observations with parallel LES and SCM simulations. We evaluate lognormal idealization of aircraft observation-derived aerosol size distributions. We test the effects of differing vertical grids and horizontal wind nudging versus geostrophic wind forcing on simulated nocturnal boundary layer and jets. We also test fixed versus time varying model top radiative flux boundary conditions. The simulated cases provide the opportunity to examine a variety of research topics including cloud type/diurnal transition, cloud entrainment, aerosol impacts, nocturnal boundary layer with evolving wind shear, and various interactions between physical processes.