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| Titel |
Long-term behavior of the concentration of the minor constituents in the mesosphere – a model study |
| VerfasserIn |
M. Grygalashvyly, G. R. Sonnemann, P. Hartogh |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 9, no. 8 ; Nr. 9, no. 8 (2009-04-27), S.2779-2792 |
| Datensatznummer |
250007212
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| Publikation (Nr.) |
 copernicus.org/acp-9-2779-2009.pdf |
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| Zusammenfassung |
| We investigate the influence the rising concentrations of methane, nitrous
oxide and carbon dioxide which have occurred since the pre-industrial era,
have had on the chemistry of the mesosphere. For this investigation we use
our global 3-D-model COMMA-IAP which was designed for the exploration of the
MLT-region and in particular the extended mesopause region. Assumptions and
approximations for the trends in the Lyman-α flux (needed for the
water vapor dissociation rate), methane and the water vapor mixing ratio at
the hygropause are necessary to accomplish this study. To approximate the
solar Lyman-α flux back to the pre-industrial time, we derived a
quadratic fit using the sunspot number record which extends back to 1749 and
is the only solar proxy available for the Lyman-α flux prior to
1947. We assume that methane increases with a constant growth rate from the
pre-industrial era to the present. An unsolved problem for the model
calculations consists of how the water vapor mixing ratio at the hygropause
should be specified during this period. We assume that the hygropause was
dryer during pre-industrial times than the present. As a consequence of
methane oxidation, the model simulation indicates that the middle atmosphere
has become more humid as a result of the rising methane concentration, but
with some dependence on height and with a small time delay of few years. The
solar influence on the water vapor mixing ratio is insignificant below about
80 km in summer high latitudes, but becomes increasingly more important
above this altitude. The enhanced water vapor concentration increases the
hydrogen radical concentration and reduces the mesospheric ozone. A second
region of stronger ozone decrease is located in the vicinity of the
stratopause. Increases in CO2 concentration enhance slightly the
concentration of CO in the mesosphere. However, its influence upon the
chemistry is small and its main effect is connected with a cooling of the
upper atmosphere. The long-term behavior of water vapor is discussed in
particular with respect to its impact on the NLC region. |
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