Assessing the Uncertainty Range of Aerosol Distributions Simulated by a Global CTM due to Different Meteorological Fields

The impact of different sets of assimilated meteorological fields on the simulated total aerosol burden and distribution is assessed in this study. Aerosol budgets and distributions from the global chemical transport model GOCART, which is driven by assimilated meteorology, have been extensively evaluated and validated in various field campaigns, and have been compared with satellite data (MODIS), with data from the AERONET network of ground stations, and with results from other models participating in the AEROCOM initiative. So far, the model results of GOCART have been obtained based on an assimilated meteorology from version 3 of the GEOS DAS of the Global Modeling and Assimilation Office. We have recently migrated to version 4 of the GEOS-DAS and will present the deviations of the total aerosol burden and of the spatial distribution from the GEOS-3 based aerosol fields. We will discuss possible causes for these differences. The 10 meter wind speed is consistently larger in GEOS-4, causing higher emissions for dust, sea salt and DMS. The higher emission rates are not offset by a corresponding higher deposition rate, since both the large scale and convective precipitation have changed significantly in GEOS-4, and also because the parameterization for in-cloud convection in GOCART was changed to be consistent with changes in the GEOS-DAS. The impact of a number of other changes will be analyzed, like the changes in the cloud fraction, the method to determine the soluble fraction of an aerosol tracer for in-cloud scavenging, and the approach to determine the updraft velocity.