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GEOPHYSICAL RESEARCH LETTERS, VOL. 30, NO. 10, 1507, doi:10.1029/2003GL017192, 2003

Sensitivity study of the spectral dispersion of the cloud droplet size distribution on the indirect aerosol effect

Yiran Peng

Department of Physics and Atmospheric Sciences, Dalhousie University, Halifax, Nova Scotia, Canada


Ulrike Lohmann

Department of Physics and Atmospheric Sciences, Dalhousie University, Halifax, Nova Scotia, Canada


Abstract

To study the influence of anthropogenic aerosols on the shape of the cloud droplet size spectra (dispersion effect), we analyze observed liquid water cloud data during two Canadian field studies. Scaled by the parameter β, which is a function of the relative dispersion of cloud droplet spectra, the calculated cloud albedo shows better agreement with the independently measured cloud albedo than the cloud albedo calculated without scaling. The scaling factor β is positively correlated with the cloud droplet number concentration. A linear relationship between β and the cloud droplet number concentration obtained from different field studies is applied to the ECHAM4 general circulation model. The global mean indirect aerosol effect at the top of atmosphere including the dispersion effect is reduced by 0.2 W m−2 as compared to the reference simulation. This accounts for about 1/3 of the reduction that needed to be imposed on the simulated anthropogenic indirect aerosol effect by Lohmann and Lesins [2002] .

Received 25 February 2003; accepted 14 April 2003; published 21 May 2003.

Index Terms: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0320 Atmospheric Composition and Structure: Cloud physics and chemistry; 1610 Global Change: Atmosphere (0315, 0325).

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Citation: Peng, Y., and U. Lohmann (2003), Sensitivity study of the spectral dispersion of the cloud droplet size distribution on the indirect aerosol effect, Geophys. Res. Lett., 30(10), 1507, doi:10.1029/2003GL017192.