Cloud droplet spectral dispersion and the indirect aerosol effect: Comparison of two treatments in a GCM, Geophys

[1] Two parameterizations of cloud droplet spectral dispersion and their impact on the indirect aerosol effect are compared in a global climate model. The earlier scheme specifies b, the ratio of droplet effective radius to volumemean radius, in terms of N, the cloud droplet number concentration. The new scheme specifies b in terms of mean droplet mass (L/N), where L is liquid water content, to account for the effect of variations in L. For low to moderate N, the new scheme gives a stronger increase of b with increasing N than the old scheme. In a present-climate simulation, the new scheme shows a stronger gradient between remote regions (small b) and polluted/continental regions (large b). The new scheme also offsets the first indirect aerosol forcing (DF) more strongly: DF = À0.65 W