Evaluating Direct Radiative Effects of Absorbing Aerosols on Atmospheric Dynamics with Aquaplanet and Regional Model Results

Abstract:

Effects of absorbing aerosol on atmospheric dynamics are usually investigated with help of general circulation models or also regional models that represent the atmospheric system as realistic as possible. Reducing the complexity of models used to study the effects of absorbing aerosol on atmospheric dynamics helps to understand underlying mechanisms. In this study, by using ECHAM6 General Circulation Model (GCM) in an Aquaplanet setting and using simplified aerosol climatology, an initial idealization step has been taken. The analysis only considers direct radiative effects, furthering the reduction of complex model results. The simulations include cases including aerosol radiative forcing, no aerosol forcing, coarse mode aerosol forcing only (as approximation for mineral dust forcing) and forcing with increased aerosol absorption. The results showed that increased absorption affects cloud cover mainly in subtropics. Hadley circulation is found to be weakened in the increased absorption case. To compare the results of the idealized model with a more realistic model setting, the results of the regional model COSMO-MUSCAT that includes interactive mineral dust aerosol and considers the effects of dust radiative forcing are also analyzed. The regional model computes the atmospheric circulation for the year 2007 twice, including the feedback of dust and excluding the dust aerosol forcing. It is investigated to which extent the atmospheric response to the dust forcing agrees with the simplified Aquaplanet results. As expected, in the regional model mineral dust causes an increase in the temperature right above the dust layer while reducing the temperature close to the surface. In both models the presence of aerosol forcing leads to increased specific humidity, close to ITCZ. Notwithstanding the difference magnitudes, comparisons of the global aquaplanet and the regional model showed similar patterns. Further detailed comparisons will be presented.