Articles | Volume 9, issue 22
Atmos. Chem. Phys., 9, 8917–8934, 2009

Special issue: European Integrated Project on Aerosol-Cloud-Climate and Air...

Atmos. Chem. Phys., 9, 8917–8934, 2009

  26 Nov 2009

26 Nov 2009

Sensitivity studies of different aerosol indirect effects in mixed-phase clouds

U. Lohmann1 and C. Hoose2 U. Lohmann and C. Hoose
  • 1Institute of Atmospheric and Climate Science, ETH Zurich, Switzerland
  • 2University of Oslo, Department of Geosciences, Oslo, Norway

Abstract. Aerosols affect the climate system by changing cloud characteristics. Using the global climate model ECHAM5-HAM, we investigate different aerosol effects on mixed-phase clouds: The glaciation effect, which refers to a more frequent glaciation due to anthropogenic aerosols, versus the de-activation effect, which suggests that ice nuclei become less effective because of an anthropogenic sulfate coating. The glaciation effect can partly offset the indirect aerosol effect on warm clouds and thus causes the total anthropogenic aerosol effect to be smaller. It is investigated by varying the parameterization for the Bergeron-Findeisen process and the threshold coating thickness of sulfate (SO4-crit), which is required to convert an externally mixed aerosol particle into an internally mixed particle. Differences in the net radiation at the top-of-the-atmosphere due to anthropogenic aerosols between the different sensitivity studies amount up to 0.5 W m−2. This suggests that the investigated mixed-phase processes have a major effect on the total anthropogenic aerosol effect.

Final-revised paper