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A Simple Model of Global Aerosol Indirect EffectsMost estimates of the global mean indirect effect of anthropogenic aerosol on the Earth's energy balance are from simulations by global models of the aerosol lifecycle coupled with global models of clouds and the hydrologic cycle. Extremely simple models have been developed for integrated assessment models, but lack the flexibility to distinguish between primary and secondary sources of aerosol. Here a simple but more physically based model expresses the aerosol indirect effect (AIE) using analytic representations of cloud and aerosol distributions and processes. Although the simple model is able to produce estimates of AIEs that are comparable to those from some global aerosol models using the same global mean aerosol properties, the estimates by the simple model are sensitive to preindustrial cloud condensation nuclei concentration, preindustrial accumulation mode radius, width of the accumulation mode, size of primary particles, cloud thickness, primary and secondary anthropogenic emissions, the fraction of the secondary anthropogenic emissions that accumulates on the coarse mode, the fraction of the secondary mass that forms new particles, and the sensitivity of liquid water path to droplet number concentration. Estimates of present-day AIEs as low as 5 W/sq m and as high as 0.3 W/sq m are obtained for plausible sets of parameter values. Estimates are surprisingly linear in emissions. The estimates depend on parameter values in ways that are consistent with results from detailed global aerosol-climate simulation models, which adds to understanding of the dependence on AIE uncertainty on uncertainty in parameter values.
Document ID
20140009177
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Ghan, Steven J. (Pacific Northwest National Lab. Richland, WA, United States)
Smith, Steven J. (Pacific Northwest National Lab. Richland, WA, United States)
Wang, Minghuai (Pacific Northwest National Lab. Richland, WA, United States)
Zhang, Kai (Pacific Northwest National Lab. Richland, WA, United States)
Pringle, Kirsty (Leeds Univ. United Kingdom)
Carslaw, Kenneth (Leeds Univ. United Kingdom)
Pierce, Jeffrey (Colorado State Univ. Fort Collins, CO, United States)
Bauer, Susanne (NASA Goddard Inst. for Space Studies New York, NY, United States)
Adams, Peter (Carnegie-Mellon Univ. Pittsburgh, PA, United States)
Date Acquired
July 15, 2014
Publication Date
June 28, 2013
Publication Information
Publication: Journal of Geophysical Research: Atmospheres
Volume: 118
Issue: 12
Subject Category
Meteorology and Climatology
Report/Patent Number
GSFC-E-DAA-TN13817
Distribution Limits
Public
Copyright
Public Use Permitted.
Keywords
Clouds
Indirect interactions
Aerosols

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