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| Titel |
The effect of horizontal gradients and spatial measurement resolution on the retrieval of global vertical NO2 distributions from SCIAMACHY measurements in limb only mode |
| VerfasserIn |
J. Puķīte, S. Kühl, T. Deutschmann, S. Dörner, P. Jöckel, U. Platt, T. Wagner |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 3, no. 4 ; Nr. 3, no. 4 (2010-08-30), S.1155-1174 |
| Datensatznummer |
250001227
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| Publikation (Nr.) |
 copernicus.org/amt-3-1155-2010.pdf |
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| Zusammenfassung |
Limb measurements provided by the Scanning Imaging Absorption spectroMeter
for Atmospheric CHartographY (SCIAMACHY) on the ENVISAT satellite allow
retrieving stratospheric profiles of various trace gases on a global scale.
Combining measurements of the same air volume from different viewing
positions along the orbit, a tomographic approach can be applied and 2-D
distribution fields of stratospheric trace gases can be acquired in one
inversion. With this approach, it is possible to improve the accounting for
the effect of horizontal gradients in the trace gas distribution on the
profile retrieval. This was shown in a previous study for the retrieval of
NO2 and OClO profiles in the Arctic region near the polar vortex boundary.
In this study, the tomographic retrieval is applied on measurements during
special limb-only orbits performed on 14 December 2008. For these orbits the
distance between consecutive limb scanning sequences was reduced to
~3.3° of the orbital circle (i.e. more than two times with
respect to the nominal operational mode). Thus, the same air volumes are
scanned successively by more than one scanning sequence also for midlatitudes
and the tropics. It is found that the profiles obtained by the tomographic
2-D approach show significant differences to those obtained by the 1-D
approach. In particular, for regions close to stratospheric transport
barriers (i.e. near to the edge of the polar vortex and subtropical
transport barrier) up to 50% larger or smaller NO2 number densities
(depending on the sign of the gradient along the line of sight) for altitudes
below the peak of the profile (around 20 km) are obtained.
The limb-only measurements allow examining the systematic error if the
horizontal gradient is not accounted for, and studying the impact of the
gradient strength on the profile retrieval on a global scale. The findings
for the actual SCIAMACHY observations are verified by sensitivity studies for
simulated data for which the NO2 distributions to be retrieved are known
in advance. In addition, the impact of the horizontal distance between
consecutive limb scanning sequences on the quality of the tomographic 2-D
retrieval is investigated and a possibility to take into account the
horizontal gradients by an interpolation approach is studied. |
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