Observational evidence of a change in radiative forcing due to the indirect aerosol effect

Anthropogenic aerosols enhance cloud reflectivity by increasing the number concentration of cloud droplets, leading to a cooling effect on climate known as the indirect aerosol effect. Observational support for this effect is based mainly on evidence that aerosol number concentrations are connected...

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Bibliographic Details
Published in:Nature
Main Authors: Penner, Joyce E., Dong, X. Q., Chen, Y.
Other Authors: Univ Michigan, Dept Atmospher Ocean & Space Sci, Ann Arbor, MI 48109 USA, Univ N Dakota, Dept Atmospher Sci, Grand Forks, ND 58202 USA, penner@umich.edu
Format: Article in Journal/Newspaper
Language:unknown
Published: Nature Publishing Group 2004
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Online Access:https://hdl.handle.net/2027.42/62920
http://www.ncbi.nlm.nih.gov/sites/entrez?cmd=retrieve&db=pubmed&list_uids=14724634&dopt=citation
https://doi.org/10.1038/nature02234
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Summary:Anthropogenic aerosols enhance cloud reflectivity by increasing the number concentration of cloud droplets, leading to a cooling effect on climate known as the indirect aerosol effect. Observational support for this effect is based mainly on evidence that aerosol number concentrations are connected with droplet concentrations, but it has been difficult to determine the impact of these indirect effects on radiative forcing(1-3). Here we provide observational evidence for a substantial alteration of radiative fluxes due to the indirect aerosol effect. We examine the effect of aerosols on cloud optical properties using measurements of aerosol and cloud properties at two North American sites that span polluted and clean conditions-a continental site in Oklahoma with high aerosol concentrations, and an Arctic site in Alaska with low aerosol concentrations. We determine the cloud optical depth required to fit the observed shortwave downward surface radiation. We then use a cloud parcel model to simulate the cloud optical depth from observed aerosol properties due to the indirect aerosol effect. From the good agreement between the simulated indirect aerosol effect and observed surface radiation, we conclude that the indirect aerosol effect has a significant influence on radiative fluxes. Peer Reviewed http://deepblue.lib.umich.edu/bitstream/2027.42/62920/1/nature02234.pdf