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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 16, issue 2
Ann. Geophys., 16, 189–196, 1998
https://doi.org/10.1007/s00585-998-0189-4
© European Geosciences Union 1998
Ann. Geophys., 16, 189–196, 1998
https://doi.org/10.1007/s00585-998-0189-4
© European Geosciences Union 1998

  28 Feb 1998

28 Feb 1998

The role of water-vapour photodissociation on the formation of a deep minimum in mesopause ozone

I. M. Vardavas1, J. H. Carver2, and F. W. Taylor3 I. M. Vardavas et al.
  • 1Department of Physics, University of Crete, and Foundation for Research and Technology − Hellas, Heraklion, GR-71409, Crete, Greece
  • 2Research School of Physical Sciences and Engineering, Institute of Advanced Studies, Australian National University, Canberra, ACT 0200, Australia
  • 3Atmospheric, Oceanic and Planetary Physics, University of Oxford, England

Abstract. A one-dimensional atmospheric photochemical model with an altitude grid of about 1.5 km was used to examine the structure of the global mean vertical ozone profile and its night-time-to-daytime variation in the upper atmosphere. Two distinct ozone layers are predicted, separated by a sharp drop in the ozone concentration near the mesopause. This naturally occurring mesopause ozone deep minimum is primarily produced by the rapid increase in the destruction of water vapour, and hence increase in HOx, at altitudes between 80 and 85 km, a region where water-vapour photodissociation by ultraviolet radiation of the solar Lyman-alpha line is significant, and where the supply of water vapour is maintained by methane oxidation even for very dry conditions at the tropospheric-stratospheric exchange region. The model indicates that the depth of the mesopause ozone minimum is limited by the efficiency with which inactive molecular hydrogen is produced, either by the conversion of atomic hydrogen to molecular hydrogen via one of the reaction channels of H with HO2, or by Lyman-alpha photodissociation of water vapour via the channel that leads to the production of molecular hydrogen. The ozone concentration rapidly recovers above 85 km due to the rapid increase in O produced by the photodissociation of O2 by absorption of ultraviolet solar radiation in the Schumann-Runge bands and continuum. Above 90 km, there is a decrease in ozone due to photolysis as the production of ozone through the three-body recombination of O2 and O becomes slower with decreasing pressure. The model also predicts two peaks in the night-time/daytime ozone ratio, one near 75 km and the other near 110 km, plus a strong peak in the night-time/daytime ratio of OH near 110 km. Recent observational evidence supports the predictions of the model.

Key words. Atmospheric composition and structure · Middle atmosphere · Thermosphere · Transmission and scattering of radiation

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