Updating the Treatment of the Direct Aerosol Effect in the Global Environmental Multiscale Model With Atmospheric Chemistry (GEM-AC)
Beale, Jennifer Lee
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Atmospheric aerosols alter the atmospheric energy budget through their scattering, absorption, and emission properties within certain spectral bands. The direct aerosol effect is a fundamental aspect of every climate and chemical transport model. Aerosol optical properties are incorporated into the Global Environmental Multiscale model with Atmospheric Chemistry (GEM-AC) which is equipped with the M7 aerosol submodel. With the recent progress in atmospheric and chemical transport modelling, an interactive dust emission scheme and a sea-state dependent sea salt emission scheme are also implemented in GEM-AC. An option between volume fraction mixing and Bruggeman mixing for the mixing state of soluble aerosols is provided. In addition, there is an option to include the aerosol direct effect at all nine longwave spectral bands in GEM-AC. Eight experiments are performed to document the new direct effect of the M7 aerosols and the effects of:the aerosols in all nine longwave spectral bands, the soluble aerosol mixing state options, the interactive dust scheme, and the sea-state dependent sea salt emission scheme. Aerosol optical properties are compared against three AERONET observation sites. Implementation of the aerosol direct effect and the new aerosol options in GEM-AC maintain the model as a practical tool for climate and chemical transport modelling.