Development of a liquid- and ice-phase cloud microphysics scheme and application in the LMDZ GCM to investigate aerosol indirect effects.
To examine the process of anthropogenic climate change using general circulation models (GCMs), it appears to be necessary to take into account not only the effect of greenhouse gases and aerosol direct radiative forcing effects, but also the impacts of aerosols on clouds and their resulting radiative forcing, the aerosol indirect effects (AIE). Like many atmospheric GCMs, the LMDZ GCM is able to treat AIE only in a very limited manner. The actual scheme uses an empirical formula to link sulfate aerosol mass to liquid water cloud droplet number concentration and only parametrizes liquid water cloud microphysics. To achieve a more realistic representation of the impact of aerosols on clouds, we introduce a more complex scheme. Cloud liquid and ice water content as well as droplet and crystal number concentrations are now treated prognostically. We calculate the formation of the precipitation species (rain, snow, and graupel) by considering several microphysical processes such as autoconversion, collection, etc. Activation of sulfate, hydrophilic organic matter, and sea salt is handled using a physically-based formula. This new scheme has been implemented in the LMDZ GCM. We show results of single-column model runs under several typical situations including the clear and polluted cases of the ACE-2 measurement campaign. First results of a 3D simulation of the GCM are presented as well and evaluated using POLDER satellite data.
EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003