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| Titel |
Daytime SABER/TIMED observations of water vapor in the mesosphere: retrieval approach and first results |
| VerfasserIn |
A. G. Feofilov, A. A. Kutepov, W. D. Pesnell, R. A. Goldberg, B. T. Marshall, L. L. Gordley, M. García-Comas, M. López-Puertas, R. O. Manuilova, V. A. Yankovsky, S. V. Petelina, J. M. Russell III |
| 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. 21 ; Nr. 9, no. 21 (2009-11-02), S.8139-8158 |
| Datensatznummer |
250007716
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| Publikation (Nr.) |
 copernicus.org/acp-9-8139-2009.pdf |
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| Zusammenfassung |
| This paper describes a methodology for water vapor retrieval in the
mesosphere-lower thermosphere (MLT) using 6.6 μm daytime broadband
emissions measured by SABER, the limb scanning infrared radiometer on board
the TIMED satellite. Particular attention is given to accounting for the
non-local thermodynamic equilibrium (non-LTE) nature of the H2O
6.6 μm emission in the MLT. The non-LTE H2O(ν2) vibrational
level populations responsible for this emission depend on energy exchange
processes within the H2O vibrational system as well as on interactions
with vibrationally excited states of the O2, N2, and CO2
molecules. The rate coefficients of these processes are known with large
uncertainties that undermines the reliability of the H2O retrieval
procedure. We developed a methodology of finding the optimal set of rate
coefficients using the nearly coincidental solar occultation H2O
density measurements by the ACE-FTS satellite and relying on the better
signal-to-noise ratio of SABER daytime 6.6 μm measurements. From this
comparison we derived an update to the rate coefficients of the three most
important processes that affect the H2O(ν2) populations in
the MLT: a) the vibrational-vibrational (V–V) exchange between the H2O
and O2 molecules; b) the vibrational-translational (V–T) process of
the O2(1) level quenching by collisions with atomic oxygen, and c) the
V–T process of the H2O(010) level quenching by collisions with
N2, O2, and O. Using the advantages of the daytime retrievals in
the MLT, which are more stable and less susceptible to uncertainties of the
radiance coming from below, we demonstrate that applying the updated
H2O non-LTE model to the SABER daytime radiances makes the retrieved
H2O vertical profiles in 50–85 km region consistent with
climatological data and model predictions. The H2O retrieval
uncertainties in this approach are about 10% at and below 70 km, 20%
at 80 km, and 30% at 85 km altitude. |
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