RACORO: An Observationally-based LES Study of Continental Boundary Layer Cumulus

Monday, May 12, 2014 - 07:00
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Three cases of boundary layer clouds are analyzed in the FAst-physics System TEstbed and Research (FASTER) project, based on continental boundary-layer-cloud observations during the RACORO Campaign [Routine Atmospheric Radiation Measurement (ARM) Aerial Facility (AAF) Clouds with Low Optical Water Depths (CLOWD) Optical Radiative Observations] at the ARM Climate Research Facility's Southern Great Plains (SGP) site. The three 60-hour case study periods are selected to capture the temporal evolution of cumulus, stratiform, and drizzling boundary-layer cloud systems under a range of conditions, intentionally including those that are relatively more mixed or transitional in nature versus being of a purely canonical type. Multi-modal and temporally varying aerosol number size distribution profiles are derived from aircraft observations. This study focuses on the first of the three cases, in which the cumulus-topped boundary layers were observed during the three daytime periods. Large eddy simulations (LESs) are performed by using the GISS Distributed Hydrodynamic Aerosol and Radiative Modeling Application (DHARMA) model and the WRF-FASTER model, which is the Weather Research and Forecasting (WRF) model implemented with forcing ingestion and other functions to constitute a flexible LES. The two LES models both capture the significant transitions of the evolving cumulus-topped boundary layers in the three daytime periods. Simulated transitions of the cloud macrophysical properties and thermodynamic structure are examined by balloon-borne soundings and ground-based remote sensors. Aircraft observations are then used to statistically evaluate the predicted cloud microphysical properties under the varying aerosol and cloud conditions. See the Vogelmann et al. poster for the related case generation and the Lin et al. poster for analysis with single-column models.

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