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Published June 27, 2007 | Supplemental Material + Published
Journal Article Open

Cloud condensation nuclei prediction error from application of Köhler theory: Importance for the aerosol indirect effect


In situ observations of aerosol and cloud condensation nuclei (CCN) and the GISS GCM Model II' with an online aerosol simulation and explicit aerosol-cloud interactions are used to quantify the uncertainty in radiative forcing and autoconversion rate from application of Köhler theory. Simulations suggest that application of Köhler theory introduces a 10–20% uncertainty in global average indirect forcing and 2–11% uncertainty in autoconversion. Regionally, the uncertainty in indirect forcing ranges between 10–20%, and 5–50% for autoconversion. These results are insensitive to the range of updraft velocity and water vapor uptake coefficient considered. This study suggests that Köhler theory (as implemented in climate models) is not a significant source of uncertainty for aerosol indirect forcing but can be substantial for assessments of aerosol effects on the hydrological cycle in climatically sensitive regions of the globe. This implies that improvements in the representation of GCM subgrid processes and aerosol size distribution will mostly benefit indirect forcing assessments. Predictions of autoconversion, by nature, will be subject to considerable uncertainty; its reduction may require explicit representation of size-resolved aerosol composition and mixing state.

Additional Information

© 2007 American Geophysical Union. Received 25 July 2006; revised 6 December 2006; accepted 27 February 2007; published 19 June 2007. We would like to acknowledge the support from a NASA EOS-IDS, an NSF CAREER award, and a Blanchard-Milliken Young Faculty Fellowship. We would also like to thank L. Oreopoulos for his thoughtful comments.

Attached Files

Published - jgrd13415.pdf

Supplemental Material - jgrd13415-sup-0001-t01.txt

Supplemental Material - jgrd13415-sup-0002-t02.txt


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