A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...

On the local and global effects of aerosol - cloud microphysics in deep convective clouds.Hans-F. Graf and Frank J. Nober, MPI for Meteorology, Hamburg, GermanyAbstract:From recent satellite observations it is evident that an increase in cloud condensation nuclei, for instancedue to biomass burning, can substantially reduce rain efficiency of convective clouds. This is potentiallyimportant for the global climate since the release of latent heat due to condensation of water vapour andfallout of rain from cumulus convection is the most important source for available potential energy in thefree troposphere. Beyond this, cumulus convection is a key process in controlling the water vapourcontent of the atmosphere. The sensitivity of the global climate to alteration of rain efficiency of convectiveclouds due to the suppression of drop coalescence by anthropogenic aerosols is studied by using theatmospheric general circulation model ECHAM4 for a 15 year sensitivity study considering the aerosoleffect on warm precipitation formation. Effects on ice processes are not included yet, and therefore theresults likely are conservative regarding the magnitude of the full effects due to suppression ofprecipitation.The main 15 year experiment allows the global dynamics to respond to the modified convective forcing,and an additional experiment with single time step analysis was performed which allows to locate and tomeasure the origin effect of aerosols on convective clouds. We found a definite perturbation of the globalcirculation, showing distinct sensitivity to the impact of aerosols on suppressing rainfall.