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| Home > Publications database > Description of the anisotropic radiation transfer model ART to dermine photodissociation coefficients |
| Book | PreJuSER-19745 |
2002
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
Please use a persistent id in citations: http://hdl.handle.net/2128/133
Report No.: Juel-3960
Abstract: All natural chemistry is driven directly or indirectly by the sunlight. Therefore, the fate of the photons coming from the sun an their way through the earth's atmosphere is essential to know if chemical processes of the biosphere or the atmosphere shall be understood. Especially in the atmosphere the processes, both physical and chemical in nature, are primarily driven by the sunlight. That is why it is so important for atmospheric models to include algorithms which simulate the photon flux through the earth's atmosphere as exactly as possible. While the dynamics of the atmosphere depend an the energy flux covering the whole wavelength regime from the vacuum ultraviolet to the far infrared, atmospheric chemistry reactions are only influenced by light of wavelengths reaching from 180 nm to 700 nm, approximately. And, moreover, the chemistry deals with the actinic flux, i. e. the number of photons passing through a volume of given size independent an the direction, as for photodissociation processes the encounter between photons and molecules is not subject to the angle of the collision. Whereas the physccs of the direct beam from the sun through the atmosphere is well understood since long, the multiple scattering of photons by molecules (Rayleigh scattering) was included in the nineteen hundred seventies in photochemical models (e. g.: Isaksen et al.,1976, Luther and Gelinas, 1976, Bahe et al., 1979). And in the eighties the scattering by aerosols and water droplets (Mie scattering) was added to the determination of photolysis coefficients, examples can be foung in Stamnes et al. (1988), Lary and Pyle (1991), Kylling et al. (1993), Ruggabber et al. (1994), Minschwaner et al. (1995), Trautmann and Box (1995), Kylling et al. (1995), Blindauer et al. (1996). In photochemical models of the atmosphere (e.g. Röth, 1980, McKenna et al., 2001) three-stream approximations of the photonflux are applied to determine photodissociation rates. These models are based an the assumption that the diffuse radiation is isotropic. To improve the three-stream models they have to be compared to more sophisticated calculations which include the anisotropy of the photonflux. Such a model is the Anisotropic Radiation Transfer Model ART, which will be described here. The purpose of the model ART is to determine the photodissociation coefficients for the interpretation of measurements of radicals. Likewise, radiometer signals [...]
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