|
Atmos. Chem. Phys. Discuss., 2, 1635-1654, 2002
www.atmos-chem-phys-discuss.net/2/1635/2002/ doi:10.5194/acpd-2-1635-2002 © Author(s) 2002. This work is licensed under a Creative Commons License. |
The H Lyman-α actinic flux in the middle atmosphere
1Institute of Meteorology and Climate Research, Forschungszentrum Karlsruhe und Universität Karlsruhe, Germany
Abstract. The penetration of solar H Lyman-a radiation into the terrestrial middle atmosphere is studied in detail. The Lyman-a actinic flux is calculated with a Monte Carlo approach including multiple resonance scattering of Lyman-a 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 O2 column densities greater than about 1024 m-2. For column densities greater than about 5 · 1024 m-2 resonance scattering becomes important at solar zenith angles > 60°. The \OD\ quantum yield of the O2 dissociation by Lyman-aphotons is found to decrease from 0.58 in the lower thermosphere to 0.48 in the lower mesosphere. Parameterisations for Lyman-a actinic flux, mean O2 absorption cross section and \OD\quantum yield including temperature dependence and resonance scattering are given valid up to a O2 column density of about 1025 m-2.
Citation: Reddmann, Th. and Uhl, R.: The H Lyman-α actinic flux in the middle atmosphere, Atmos. Chem. Phys. Discuss., 2, 1635-1654, doi:10.5194/acpd-2-1635-2002, 2002.