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| Titel |
Model studies of the influence of O2 photodissociation parameterizations in the Schumann-Runge bands on ozone related photolysis in the upper atmosphere |
| VerfasserIn |
Gijs A. A. Koppers, Donal P. Murtagh |
| 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 ; 14, no. 1 ; Nr. 14, no. 1, S.68-79 |
| Datensatznummer |
250012138
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| Publikation (Nr.) |
 copernicus.org/angeo-14-68-1996.pdf |
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| Zusammenfassung |
| A new parameterization for atmospheric
transmission and O2 photodissociation in the Schumann-Runge band
region has been developed and tested with a 1D radiative-photochemical model.
The parameterization is based on the O2-column along the line of
sight to the Sun and the local temperature. Line-by-line calculations have
served as a benchmark for testing this method and several other, commonly used,
parameterizations. The comparisons suggest that differences between the
line-by-line calculations and currently accepted parameterizations can be
reduced significantly by using the new method, particularly at large solar
zenith angles. The production rate of O-atoms computed with this method shows
less than 6% deviation compared to the line-by-line calculations at any
altitude, all solar zenith angles and in all seasons. The largest errors are
found toward the shorter wavelengths in the Schumann-Runge region at low
altitudes. Transmittance is approximated to better than 4% at any altitude
and/or solar zenith angle. The total O-production rate above 20 km is
approximated to better than 2%. The new parameterization is easily implemented
in existing photochemical models and in many cases it may simply replace the
existing algorithm. The computational effort exceeds that of other
parameterizations but in view of the total computation time needed for the
actual calculation of the parameterized Schumann-Runge bands this should not
lead to significant performance degeneration. The first 14 coefficients of the
parameterization are included in this study. Both the complete sets of
coefficients and a simple algorithm can be obtained by contacting the authors. A
photochemical model study shows the largest effect of the parameterization
method is on odd hydrogen concentrations. Subsequent interaction with an odd
oxygen family causes differences in the ozone concentrations between the
different parameterizations of more than 10% at selected altitudes. Although it
is already established that deficiencies in the treatment of Schumann-Runge band
absorption are unlikely to explain the current underestimation of ozone
concentration at the stratopause in a variety of photochemical models, this
study does show that the choice of parameterization has a large impact on the
accuracy of the results at large solar zenith angles and in different seasons. |
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