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| Titel |
Quantifying lower tropospheric methane concentrations using GOSAT near-IR and TES thermal IR measurements |
| VerfasserIn |
J. R. Worden, A. J. Turner, A. Bloom, S. S. Kulawik, J. Liu, M. Lee, R. Weidner, K. Bowman, C. Frankenberg, R. Parker, V. H. Payne |
| 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 ; 8, no. 8 ; Nr. 8, no. 8 (2015-08-25), S.3433-3445 |
| Datensatznummer |
250116541
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| Publikation (Nr.) |
 copernicus.org/amt-8-3433-2015.pdf |
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| Zusammenfassung |
| Evaluating surface fluxes of CH4 using total column data requires
models to accurately account for the transport and chemistry of methane in
the free troposphere and stratosphere, thus reducing sensitivity to the
underlying fluxes. Vertical profiles of methane have increased sensitivity
to surface fluxes because lower tropospheric methane is more sensitive to
surface fluxes than a total column, and quantifying free-tropospheric
CH4 concentrations helps to evaluate the impact of transport and
chemistry uncertainties on estimated surface fluxes. Here we demonstrate the
potential for estimating lower tropospheric CH4 concentrations through
the combination of free-tropospheric methane measurements from the Aura
Tropospheric Emission Spectrometer (TES) and XCH4 (dry-mole air
fraction of methane) from the Greenhouse gases Observing SATellite – Thermal
And Near-infrared for carbon Observation (GOSAT TANSO, herein GOSAT for
brevity). The calculated precision of these estimates ranges from 10 to 30 ppb
for a monthly average on a 4° × 5° latitude/longitude grid making
these data suitable for evaluating lower-tropospheric methane
concentrations. Smoothing error is approximately 10 ppb or less. Comparisons
between these data and the GEOS-Chem model demonstrate that these
lower-tropospheric CH4 estimates can resolve enhanced concentrations
over flux regions that are challenging to resolve with total column
measurements. We also use the GEOS-Chem model and surface measurements in
background regions across a range of latitudes to determine that these
lower-tropospheric estimates are biased low by approximately 65 ppb, with an
accuracy of approximately 6 ppb (after removal of the bias) and an actual
precision of approximately 30 ppb. This 6 ppb accuracy is consistent with
the accuracy of TES and GOSAT methane retrievals. |
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