The H Lyman-a actinic flux in the middle atmosphere

Other literature type English OPEN
Reddmann, T. ; Uhl, R. (2003)

The penetration of solar H Lyman-<font face="Symbol"><b>a</b></font> radiation into the terrestrial middle atmosphere is studied in detail. The Lyman-<font face="Symbol"><b>a</b></font> actinic flux is calculated with a Monte Carlo approach including multiple resonance scattering of Lyman-<font face="Symbol"><b>a</b></font> photons within the terrestrial atmosphere and a temperature dependent absorption cross section of molecular oxygen. The dependence of the actinic flux on the temperature profile is significant for O<sub>2</sub> column densities greater than about 10<sup>24</sup> m<sup>-2</sup>. For column densities greater than about 5 <b>·</b> 10<sup>24</sup> m<sup>-2</sup> resonance scattering becomes important at solar zenith angles &gt; 60°. The O(<sup>1</sup>D) quantum yield of the O<sub>2</sub> dissociation by Lyman-<font face="Symbol"><b>a</b></font> photons is found to decrease from 0.58 in the lower thermosphere to 0.48 in the lower mesosphere. Parameterisations for Lyman-<font face="Symbol"><b>a</b></font> actinic flux, mean O<sub>2</sub> absorption cross section and O(<sup>1</sup>D) quantum yield including temperature dependence and resonance scattering are given valid up to a O<sub>2</sub> column density of about 10<sup>25</sup> m<sup>-2</sup>.
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