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| Titel |
Tropospheric column ozone: matching individual profiles from Aura OMI and TES with a chemistry-transport model |
| VerfasserIn |
Q. Tang, M. J. Prather |
| 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 ; 12, no. 21 ; Nr. 12, no. 21 (2012-11-08), S.10441-10452 |
| Datensatznummer |
250011575
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| Publikation (Nr.) |
 copernicus.org/acp-12-10441-2012.pdf |
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| Zusammenfassung |
| Of all satellite measurements of ozone, only two instruments have coincident,
spatially overlapping measurements to allow direct comparison of tropospheric
column ozone (TCO): the Ozone Monitoring Instrument (OMI) and the
Tropospheric Emission Spectrometer (TES) on the NASA Aura spacecraft. For two
years (2005–2006), we collect all observations between 60° S and
60° N from nadir (~65 000 from OMI and TES) and cross-track
swaths (~30 000 000 from OMI) and compare with a chemistry-transport
model (CTM) simulating each observation with corresponding spatial and
temporal coincidence. High-frequency TCO variations are indicative of
stratospheric intrusions of ozone-rich air, and the individual, level 2 data
provide access to these short-lived phenomena. Although we can identify some
seasonal and large-scale biases in the model, the CTM as a transfer standard
identifies weaknesses in the observations and further helps quantify the
measurement noise of individual profiles. The relatively noise-free CTM
bridges these two satellite measurements and improves their cross-validation
to better precision than a simple direct comparison. Previous validation
studies of TES TCO versus ozonesondes found a bias of about +4 Dobson Units
(DU) for large regions. The three-way comparison and the CTM transfer method
that use a far greater number of coincidences, indicate that monthly zonal
mean OMI-TES TCO biases fall within 5–10%, and thus quantifies the zonal
mean OMI TCO bias at a few DU. For small regions (i.e.,
5 × 5°), however, the monthly mean OMI-TES differences can
exceed ±10 DU at many places (e.g., tropics for the direct OMI-TES
comparison) due to different tropospheric sensitivities of the two
instruments at these locations. Partly removing the influence of different
sensitivities by applying the CTM as the transfer standard, the OMI-TES
differences generally decrease, especially over the tropics. In addition, the
CTM-TES comparison split into day versus night observations shows no apparent
bias in TES at very low levels, ±1 DU. These OMI-TES-CTM comparisons
highlight the importance of the a priori ozone profiles that went into each
satellite retrieval, including a false agreement due to CTM-a priori
similarity, and the importance of including the vertical information (i.e.,
averaging kernel) in the retrieval products. This study also highlights the
advantages of overlapping measurements in terms of cross-validation and the
application of a model as the transfer standard. |
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