Sensitivity of the total anthropogenic aerosol effect to the treatment of rain in a global climate model

Abstract

This study investigates the sensitivity of the total anthropogenic aerosol effect to the treatment of rain within the global climate model (GCM) ECHAM5. A. comparison between a prognostic (rain is stored within the atmosphere) and a diagnostic rain scheme (rain is precipitated out within one model time step) is conducted. Furthermore, the shape of the rain drop distribution within the prognostic rain scheme is varied. The prognostic rain scheme shifts the emphasis of the rain production process from autoconversion to accretion in better agreement with observations. Since the parameterization of the accretion process is independent of the cloud droplet number concentration, the total anthropogenic aerosol effect decreased by 0.5 to 0.9 Wm-2. Varying the rain drop distribution has a smaller influence on the total anthropogenic aerosol effect, changing it by 0.2 to 0.3 Wm-2. Copyright 2009 by the American Geophysical Union.