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| Titel |
Profiles of CH4, HDO, H2O, and N2O with improved lower tropospheric vertical resolution from Aura TES radiances |
| VerfasserIn |
J. Worden, S. Kulawik, C. Frankenberg, V. Payne, K. Bowman, K. Cady-Peirara, K. Wecht, J.-E. Lee, D. Noone |
| 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 ; 5, no. 2 ; Nr. 5, no. 2 (2012-02-20), S.397-411 |
| Datensatznummer |
250002466
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| Publikation (Nr.) |
 copernicus.org/amt-5-397-2012.pdf |
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| Zusammenfassung |
| Thermal infrared (IR) radiances measured near 8 microns contain information
about the vertical distribution of water vapor (H2O), the water
isotopologue HDO, and methane (CH4), key gases in the water and carbon
cycles. Previous versions (Version 4 or less) of the TES profile retrieval
algorithm used a "spectral-window" approach to minimize uncertainty from
interfering species at the expense of reduced vertical resolution and
sensitivity. In this manuscript we document changes to the vertical
resolution and uncertainties of the TES version 5 retrieval algorithm. In
this version (Version 5), joint estimates of H2O, HDO, CH4 and
nitrous oxide (N2O) are made using radiances from almost the entire
spectral region between 1100 cm−1 and 1330 cm−1. The TES retrieval
constraints are also modified in order to better use this information. The
new H2O estimates show improved vertical resolution in the lower
troposphere and boundary layer, while the new HDO/H2O estimates can now
profile the HDO/H2O ratio between 925 hPa and 450 hPa in the tropics
and during summertime at high latitudes. The new retrievals are now
sensitive to methane in the free troposphere between 800 and 150 mb with
peak sensitivity near 500 hPa; whereas in previous versions the sensitivity
peaked at 200 hPa. However, the upper troposphere methane concentrations are
biased high relative to the lower troposphere by approximately 4% on
average. This bias is likely related to temperature, calibration, and/or
methane spectroscopy errors. This bias can be mitigated by normalizing the
CH4 estimate by the ratio of the N2O estimate relative to the
N2O prior, under the assumption that the same systematic error affects
both the N2O and CH4 estimates. We demonstrate that applying this
ratio theoretically reduces the CH4 estimate for non-retrieved
parameters that jointly affect both the N2O and CH4 estimates. The
relative upper troposphere to lower troposphere bias is approximately
2.8% after this bias correction. Quality flags based upon the vertical
variability of the methane and N2O estimates can be used to reduce this
bias further. While these new CH4, HDO/H2O, and H2O estimates
are consistent with previous TES retrievals in the altitude regions where
the sensitivities overlap, future comparisons with independent profile
measurement will be required to characterize the biases of these new
retrievals and determine if the calculated uncertainties using the new
constraints are consistent with actual uncertainties. |
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