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| Titel |
Hydroxyl layer: trend of number density and intra-annual variability |
| VerfasserIn |
G. R. Sonnemann, P. Hartogh, U. Berger, M. Grygalashvyly |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 33, no. 6 ; Nr. 33, no. 6 (2015-06-17), S.749-767 |
| Datensatznummer |
250121213
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| Publikation (Nr.) |
 copernicus.org/angeo-33-749-2015.pdf |
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| Zusammenfassung |
| The layer of vibrationally excited hydroxyl (OH*) near the mesopause in
Earth's atmosphere is widely used to derive the temperature at this height
and to observe dynamical processes such as gravity waves. The concentration
of OH* is controlled by the product of atomic hydrogen, with ozone creating a
layer of enhanced concentration in the mesopause region. However, the basic
influences on the OH* layer are atomic oxygen and temperature. The long-term
monitoring of this layer provides information on a changing atmosphere. It
is important to know which proportion of a trend results from anthropogenic
impacts on the atmosphere and which proportion reflects natural variations. In a
previous paper (Grygalashvyly et al., 2014), the trend of the height of the
layer and the trend in temperature were investigated particularly in midlatitudes on the basis of our coupled dynamic and chemical transport model
LIMA (Leibniz Institute Middle Atmosphere). In this paper we consider the
trend for the number density between the years 1961 and 2009 and analyze the
reason of the trends on a global scale. Further, we consider intra-annual
variations. Temperature and wind have the strongest impacts on the trend.
Surprisingly, the increase in greenhouse gases (GHGs) has no clear influence
on the chemistry of OH*. The main reason for this lies in the fact that, in
the production term of OH*, if atomic hydrogen increases due to increasing
humidity of the middle atmosphere by methane oxidation, ozone decreases. The
maximum of the OH* layer is found in the mesopause region and is very
variable. The mesopause region is a very intricate domain marked by
changeable dynamics and strong gradients of all chemically active minor
constituents determining the OH* chemistry. The OH* concentration responds,
in part, very sensitively to small changes in these parameters. The cause
for this behavior is given by nonlinear reactions of the photochemical
system being a nonlinear enforced chemical oscillator driven by the
diurnal-periodic solar insolation. At the height of the OH* layer the system
operates in the vicinity of chemical resonance. The solar cycle is mirrored
in the data, but the long-term behavior due to the trend in the Lyman-α
radiation is very small. The number density shows distinct hemispheric
differences. The calculated OH* values show sometimes a step around a
certain year. We introduce a method to find out the date of this step and
discuss a possible reason for such behavior. |
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