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GEOPHYSICAL RESEARCH LETTERS, VOL. 33, L05816, doi:10.1029/2005GL025148, 2006

CCN predictions: Is theory sufficient for assessments of the indirect effect?

Rafaella-Eleni P. Sotiropoulou

School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia, USA


Jeessy Medina

School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia, USA


Athanasios Nenes

School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia, USA
School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia, USA


Abstract

This study quantitatively assesses the sensitivity of cloud droplet number (CDNC) to errors in cloud condensation nuclei (CCN) predictions that arise from application of Köhler theory. The CDNC uncertainty is assessed by forcing a droplet activation parameterization with a comprehensive dataset of CCN activity and aerosol size and chemical composition obtained during the ICARTT field campaign in August 2004. Our analysis suggests that, for a diverse range of updraft velocity, droplet growth kinetics and airmass origin, the error in predicted CDNC is (at most) half of the CCN prediction error. This means that the typical 20–50% error in ambient CCN closure studies would result in a 10–25% error in CDNC. For the first time, a quantitative link between aerosol and CDNC prediction errors is available, and can be the basis of a robust uncertainty analysis of the first aerosol indirect effect.

Received 6 November 2005; accepted 25 January 2006; published 15 March 2006.

Index Terms: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801, 4906); 0345 Atmospheric Composition and Structure: Pollution: urban and regional (0305, 0478, 4251); 1625 Global Change: Geomorphology and weathering (0790, 1824, 1825, 1826, 1886); 3311 Atmospheric Processes: Clouds and aerosols.

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Citation: Sotiropoulou, R.-E. P., J. Medina, and A. Nenes (2006), CCN predictions: Is theory sufficient for assessments of the indirect effect?, Geophys. Res. Lett., 33, L05816, doi:10.1029/2005GL025148.