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A tool that simulates realistic aerosol scenarios for climatic applications Is presented and discussed.
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Aerosols have an uncertain effect on climate (Alexander et al. 2013) and serious impacts on human health (Nel 2005). Aerosols directly affect climate by modifying Earth's energy budget, known as radiative forcing. A net positive forcing tends to heat Earth, while a negative forcing tends to cool it down. Aerosols also modify cloud microphysical properties and albedo and thus impact precipitation (indirect radiative effects). For example, Saharan and Asian dust and biological aerosols probably serve as ice nuclei and play an important role in orographic precipitation processes over the western United States (Creamean et al. 2013). In addition, aerosols interact with other elements of the Earth system. For instance, mineral dust aerosols are a source of iron for ocean biogeochemistry, the deposition of mineral dust and black carbon (BC) aerosols decreases the albedo of snow and ice, and aerosol influences vegetation growth by modifying the photosynthetically active radiation [Bellouin et al. (2011); and references therein].
Because aerosols are not well mixed throughout the atmosphere, simulations are one of the only methods of estimating their average climate effect (Myhre et al. 2013), the other method involving interpretation of satellite and ground-based measurements (Holben et al. 1998; Remer et al. 2008). The radiative forcing of the total aerosol effect in the atmosphere, which includes cloud adjustments due to aerosols, is -0.9 W nr2 (from -1.9 to -0.1 W m-2) (medium confidence). There is a negative forcing from most aerosols and a positive contribution from black carbon absorption of solar radiation (Alexander et al. 2013). The main cause of the uncertainty is the differences between estimates from global aerosol models and observation-based estimates, with the latter tending to have stronger (more negative) radiative forcing (Myhre 2009). Since radiative forcing estimates from observational data are currently not possible, they must, at least partly, rely on global aerosol models (Myhre 2009). An additional source of uncertainty is the aerosols, altitude. Samset and Myhre (2011) analyzed the sensitivity with the aerosol vertical distribution of the normalized direct radiative forcing (NDRF)-that is, direct radiative forcing divided by the burden (mg m-2). The authors found a tenfold increase in the NDRF for BC...