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| Titel |
Impact of temperature field inhomogeneities on the retrieval of atmospheric species from MIPAS IR limb emission spectra |
| VerfasserIn |
M. Kiefer, E. Arnone, A. Dudhia, M. Carlotti, E. Castelli, T. Clarmann, B. M. Dinelli, A. Kleinert, A. Linden, M. Milz, E. Papandrea, G. Stiller |
| 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. 5 ; Nr. 3, no. 5 (2010-10-29), S.1487-1507 |
| Datensatznummer |
250001305
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| Publikation (Nr.) |
 copernicus.org/amt-3-1487-2010.pdf |
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| Zusammenfassung |
| We examine volume mixing ratios (vmr) retrieved from limb emission spectra
recorded with the Michelson Interferometer for Passive Atmospheric Sounding
(MIPAS) on board Envisat. In level 2 (L2) data products of three different retrieval
processors, which perform one dimensional (1-D) retrievals, we find
significant differences between species' profiles from ascending and
descending orbit parts. The relative differences vary systematically with
time of the year, latitude, and altitude. In the lower stratosphere their
monthly means can reach maxima of 20% for CFC-11, CFC-12, HNO3, H2O,
10% for CH4 and N2O. Relative differences between monthly means of
1-D retrieval results and of the true atmospheric state can be expected to
reach half of these percentage values, while relative differences in single
vmr profiles might well exceed those numbers. Often there are no physical or
chemical reasons for these differences, so they are an indicator for a
problem in the data processing. The differences are generally largest at
locations where the meridional temperature gradient of the atmosphere is
strong. On the contrary, when performing the retrieval with a tomographic two
dimensional (2-D) retrieval, L2 products generally do not show these
differences. This suggests that inhomogeneities in the temperature field, and
possibly in the species' fields, which are accounted for in the 2-D algorithm
and not in standard 1-D processors, may cause significant deviations in the
results. Inclusion of an externally given adequate temperature gradient in
the forward model of a 1-D processor helps to reduce the observed
differences. However, only the full tomographic 2-D approach is suitable to
resolve the horizontal inhomogeneities. Implications for the use of the 1-D
data, e.g. for validation, are discussed. The dependence of the
ascending/descending differences on the observation strategy suggests that
this problem may affect 1-D retrievals of
infrared limb sounders, if the line of sight of the instrument has a
significant component in the direction of the horizontal temperature
variation. |
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