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| Titel |
Simultaneous retrieval of tropospheric CO2 and CH4 in the tropics: almost two years from IASI hyperspectral infrared observations. |
| VerfasserIn |
C. Crevoisier, D. Nobileau, A. Chédin, A. M. Fiore, R. Armante |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250027185
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| Zusammenfassung |
| Coupled observations from the Infrared Atmospheric Sounding Interferometer (IASI) and
from the Advanced Microwave Sounding Unit (AMSU), launched together onboard the
European MetOp platform in October 2006, are used to retrieve mid-to-upper tropospheric
contents of carbon dioxide (CO2) and methane (CH4) in clear-sky conditions, in
the tropics, since the first month of operation of MetOp (July 2007). In April, 20
months will be available. With its very high spectral resolution, IASI provides a few
channels located either in the 15 μm band or in the 7.7 μm band highly sensitive to,
respectively, CO2 and CH4, with reduced sensitivities to other atmospheric variables.
These channels, sensitive to both temperature and either CO2 or CH4, are used in
conjunction with AMSU channels, only sensitive to temperature, to decorrelate
both signals through a non-linear inference scheme based on neural networks. A
key point of this approach is that no use is made of prior information in terms of
gas seasonality, trend, or geographical patterns. The accuracy of the retrieval is
estimated to be about 2 ppmv (less than 1%) for CO2 and 16 pbbv (~0.9%) for CH4.
Features of the retrieved methane space-time distribution include: (1) a strong seasonal
cycle in the northern tropics, and a lower seasonal cycle in the southern tropics,
in agreement with in-situ measurements; (2) a latitudinal decrease from 20-N to
20-S lower than what is observed at the surface but in excellent agreement with
tropospheric aircraft measurements; (3) geographical patterns in good agreement with
simulations from atmospheric transport and chemistry models, but with a higher
variability; (4) signatures of CO2/CH4 emissions transported to the troposphere such as a
large plume of elevated tropospheric methane south of the Asian continent, which
might be due to Asian emissions from rice paddies uplifted by deep convection
during the monsoon period and then transported towards Indonesia. In addition to
bringing a greatly improved view of CO2 and CH4 distribution, these results from
IASI should provide a means to observe and understand atmospheric transport
pathways of these two greenhouse gases from the surface to the upper troposphere. |
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