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Atmospheric Composition

Well-known for their central role in climate change, clouds are formed by condensation and deposition of water vapor on the aerosols that get activated as cloud condensation nuclei (CCN) or cloud-ice nuclei (IN). The number of cloud particles (droplets and ice crystals) and their size distribution therefore critically depends on the number of activated aerosols. Nucleation, however, is only the first of a series of cloud processes, such as cloud particle growth, cloud dissipation, radiative forcing, and precipitation. Each of these depends on the cloud particle concentration, and therefore linked to indirect aerosol effects. General circulation models (GCMs) are an important tool for understanding the climate response to changes in the amounts and composition of aerosols due to evolving use of fossil and biomass fuels. Confidence in GCM simulations of aerosol-cloud-radiation interactions requires physically robust and properly validated representations of aerosol nucleation, in addition to cloud dynamics in the model. To effectively attack the cloud parameterization problem as a whole, we have developed and used McRAS, which has proven to be a successful cloud scheme, particularly with regard to representing tropical features, including 30-60 day oscillations. We have also synthesized four aerosol cloud interaction modules for aerosol indirect effects (AIE), namely separate modules for aerosol activation of water and ice clouds, precipitation microphysics, and a methodology for determining the effective radius of water droplet distributions. These have been successully incorporated into the GEOS-4 GCM. Now that the GEOS-5 GCM has been adapted for use within the Earth System Modeling Framework (ESMF), and has fully prognostic aerosol and cloud sub-models and an interactive ocean model, the configuration is ideal for studies of aerosol-cloud-radiation interactions using the McRAS and AIE parameterization suite. We propose to implement McRAS and our AIE scheme into the GEOS-5 GCM, resolve some of the outstanding issues related to IN and the optical thickness of ice clouds by invoking ammonium sulfate as a new IN, improve the radiative transfer for the best possible cloud-radiative interactions, and then perform simulations studies to understand the connections among aerosol, weather and climate. The research will involve extensive evaluation and model performance optimization, detailed examination of simulated statistics of various interactions, and selected case studies.

Project PI: Yogesh Sud/NASA Goddard Space Flight Center

Phone: (301) 614-6240

Email: yogesh.c.sud@nasa.gov

http://climate.gsfc.nasa.gov/userpage/sud

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Started: Aug 10, 2010

Last Activity: Dec 15, 2010

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