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Aerosol-Cloud-Radiation Interaction: A Comparison of GCM Results versus Surface Observations

Liepert, B.G., Lamont-Doherty Earth Observatory of Columbia University; Lohmann, U., Dalhousie University, Halifax, Canada
Ninth Atmospheric Radiation Measurement (ARM) Science Team Meeting

The change in cloud properties due to increased anthropogenic emissions of aerosols and their precursor gases is referred to as "indirect aerosol effect." Estimates with general circulation models (GCMs) assumed that an increase in aerosol concentration would lead to a cooling effect of about -1Wm2. To evaluate the anthropogenic indirect aerosol effect, we compared two ECHAM GCM experiments with long-term surface observations covering the United States and Germany. The model prognosticates the number of cloud droplets and parameterizes cloud droplet nulceation as a function of total aerosol number concentration, updraft velocity and an aerosol shape parameter. Two experiments will be shown: one run with pre-industrial and the other run with present-day sulfate aerosol concentrations. The modeled solar radiation fluxes and total cloud coverage were then compared with surface climatologies for selected regions in the United States and Germany. The clear-sky, overcast and all-sky climatologies are composites of long-term broadband solar radiation measurements and cloud cover observations. Monthly means and frequency distributions of total cloud coverage as well as annual cycles of surface solar fluxes will be presented and discussed.

Note: This is the poster abstract presented at the meeting; an extended version was not provided by the author(s).