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Titel |
A new method to investigate regional scale carbon budgets from satellite measured carbon dioxide. |
VerfasserIn |
A. J. Hewitt, H. Boesch, M. P. Barkley, A. Manning, C. Witham, P. S. Monks |
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 |
250025897
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Zusammenfassung |
The existing generation of satellite instruments (such as SCIAMACHY and AIRS) have
allowed the retrieval of atmospheric mixing ratios of carbon dioxide. This data can be used to
investigate carbon fluxes between the surface and the atmosphere. This information can
compliment existing flux information from the high precision but low density network of
surface and tower measurements, and could improve carbon cycle understanding in remote
regions not covered by this network. This understanding will be further improved
by the OCO and GOSAT missions, which are expected to be launched early in
2009.
A method has been developed to investigate regional scale carbon budgets, based on the
UK met office Lagrangian trajectory model NAME (Numerical Atmospheric-dispersion
Modelling Environment). The model provides information about where an air mass that has
been sampled by the satellite instrument has come from. This provides both residence time
information over various parts of the land surface, as well as information about where the air
mass originated from.
The method can be used in forward mode, where we can use flux information from
another source, for example carbon tracker data, and combine this with a background CO2
mixing ratio to obtain an atmospheric concentration at the same place as the satellite
measurement, allowing a comparison between the two.
Producing the background value (the initialisation) is the most challenging part of the
method. Ideally, the background mixing ratio would also be obtained from the satellite
instrument, from measurements over areas of negligible surface fluxes (background
measurements over ocean, when investigating the land surface exchanges is not
unreasonable).
The NAME model can provide information on where and when to take the background
measurement. The air mass, from which the foreground measurement is made, is likely to
have dispersed by the time the background measurement is made, which adds to this
challenge.
The model can also be run in inverse mode, where the change in carbon mass between the
foreground and background measurements, can be combined with the residence times from
the NAME model. With the assumption that the region is made up of homogeneous flux
ecoregions (sub-regions that are believed to have very similar flux behaviour, because they
have similar weather), flux values can be assigned to the ecoregions which provide the best
match with the observed mass exchange between foreground and background satellite
measurements.
As a test case, we have demonstrated the method using the FSI-WFM-DOAS (University
of Leicester) algorithm retrievals from SCIAMACHY over the North American region. This
will provide the best place to compare our method with the wealth of other CO2 mixing ratios
and fluxes from top-down (Carbon Tracker) and bottom-up (Ameriflux) networks. |
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