Interaction of Aerosols with Radiation

The first application is the simulation of a mineral dust event over West Africa in March 2004. During this event there were high wind speeds and low temperature observed in the Sahara and heavy precipitations over Libya (Knipperts and Fink 2006). Figure 6.2 shows the simulated dust loading for 4th March 2004 at 12 UTC. To investigate the impact of the dust aerosols on radiation two simulations were performed one with no interaction between the actual aerosol concentration and radiation, and another that takes into account the interaction. 

Fig. 6.5 Difference of the shortwave radiation balance (a) and the temperature (b) between the model run with aerosol-radiation interaction and the run without aerosol-radiation interaction...

At the moment the cloud microphysics-aerosol interaction is included in HIRLAM in a very simple way in the convection schemes, where the cloud condensation nuclei have a lower concentration than over land. Enviro-HIRLAM includes the aerosol dynamics and their indirect effects on meteorology. The use of aerosol may also be prepared by making a 3D field of aerosol that has the characteristics of the currently prescribed values, then the extension to a real 3D distribution of aerosols that can interact with the microphysics is relatively straightforward. Sensitivity studies are needed to understand the relative importance of feedbacks. First experience of Enviro-HIRLAM indicates some sensitivity to effective droplet size modification in radiation and clouds. 

Total effect not equal to sum of individual effects due to interactions. Cloud cover changes unknown. Effects shown for either an increase or a decrease. Specifically aerosols with high single scattering albedos (e.g., sulfates) which refiect UV radiation back to space. Specifically aerosols with low single scattering albedos (e.g., black carbon) which absorb UV radiation. Madronich and Granier (1992) and Krol et al. (1998). 

Figure 15.1 depicts the various processes that can occur when radiation of wavelength X0 interacts with a particle. Inelastic scattering processes include Raman scattering and fluorescence. For the interaction of solar radiation with atmospheric aerosols, elastic light scattering is the process of interest. 

Aerosols, including those of biogenic origin, have important impacts on atmospheric radiation, both directly, and indirectly through the nucleation of atmospheric water. The impact of biogenic aerosols on radiation through direct and indirect effects depends on their physical and chemical properties. Table 5 shows the main chemical and physical properties of aerosols that influence their interaction with radiation, and with other atmospheric compounds, resulting in the formation of secondary particles, as well as their influence on cloud formation. Chemical... 

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