Aerosol/Boundary Layer Cloud Interactions--Simulations and Parameterization Testing

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Intellectual Merit. This research focuses on improving understanding of precipitating boundary layer clouds and developing parameterizations of those clouds for use in larger scale models such as general circulation climate models (GCM) and operational forecast models. The Principal Investigator (PI) will perform large-eddy simulations (LES) of precipitating trade wind cumuli for selected cases observed during the recent Rain in Cumulus over the Ocean (RICO) Experiment field campaign. In particular, the PI will examine how variations in the concentrations of cloud condensation nuclei (CCN) and giant cloud condensation nuclei (GCCN) alter the ensemble-averaged properties of clouds such as cloud cover, average liquid water contents, cloud lifetimes, vertical velocity spectra, cloud radiative properties, and rainfall. Because RICO is one of the few field campaigns that provides measurements of thermodynamics, winds, and CCN and GCCN concentrations, as well as in situ airborne and radar measurements of cloud properties, it provides a unique opportunity to test the performance of precipitating LES models, parameterized microphysics, and single-column models of the cloudy precipitating boundary layer. It is anticipated that these simulations will also contribute to furthering fundamental understanding of aerosol cloud interactions in the trade wind regime. Moreover, RICO provides a unique opportunity to calibrate and test a parameterized regional cloud nucleating aerosol source-sink/transport model under development. In addition, the PI will calibrate and test this cloud-nucleating aerosol model using data collected in other field campaigns that have obtained measurements of at least some components of these important aerosols. The aerosol source model coupled to cloud-resolving and mesoscale models will then be used to examine the potential variability of cloud properties and precipitation at various locations around the world. Broader Impacts. Research is suggesting that variability of cloud nucleating aerosol concentrations can have appreciable impacts on climate simulations and forecasts, and on quantitative precipitation forecasts. The modeling studies are designed to further quantify the role of those aerosols on cloud properties and precipitation. In addition, the parameterized cloud models and cloud-nucleating aerosol source model being developed and tested are designed such that they could be migrated into operational medium range and long range forecast models which could lead to improved forecasts of weather and climate.