Constraining the total aerosol indirect effect in the LMDZ and ECHAM4 GCMs using MODIS satellite data J. Quaas1,3, O. Boucher2,3, and U. Lohmann4 1Max Planck Institute for Meteorology, Hamburg, Germany 2Laboratoire d’Optique Atmosphérique, CNRS/Université des Sciences et Technologies de Lille, Villeneuve d’Ascq, France 3Hadley Centre, Met Office, Exeter, UK 4Institute for Atmospheric and Climate Science, ETH Zurich, Switzerland
Abstract. Aerosol indirect effects are considered to be the most uncertain yet
important anthropogenic forcing of climate change. The goal of the present
study is to reduce this uncertainty by constraining two different general
circulation models (LMDZ and ECHAM4) with satellite data. We build a
statistical relationship between cloud droplet number concentration and the
optical depth of the fine aerosol mode as a measure of the aerosol indirect
effect using MODerate Resolution Imaging Spectroradiometer (MODIS) satellite
data, and constrain the model parameterizations to match this relationship.
We include here "empirical" formulations for the cloud albedo effect as
well as parameterizations of the cloud lifetime effect. When fitting the
model parameterizations to the satellite data, consistently in both models,
the radiative forcing by the combined aerosol indirect effect is reduced
considerably, down to
−0.5 and −0.3 Wm−2, for LMDZ and ECHAM4, respectively.
Citation: Quaas, J., Boucher, O., and Lohmann, U.: Constraining the total aerosol indirect effect in the LMDZ and ECHAM4 GCMs using MODIS satellite data, Atmos. Chem. Phys., 6, 947-955, doi:10.5194/acp-6-947-2006, 2006.