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| Titel |
Spatial and temporal resolution of carbon flux estimates for 1983-2002 |
| VerfasserIn |
L. M. P. Bruhwiler, A. M. Michalak, P. P. Tans |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 8, no. 5 ; Nr. 8, no. 5 (2011-05-26), S.1309-1331 |
| Datensatznummer |
250005824
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| Publikation (Nr.) |
 copernicus.org/bg-8-1309-2011.pdf |
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| Zusammenfassung |
We discuss the spatial and temporal resolution of monthly carbon flux
estimates for the period 1983–2002 using a fixed-lag Kalman Smoother
technique with a global chemical transport model, and the GLOBALVIEW data
product. The observational network has expanded substantially over this
period, and the flux estimates are better constrained provided by
observations for the 1990's in comparison to the 1980's. The estimated
uncertainties also decrease as observational coverage expands. In this study,
we use the Globalview data product for a network that changes every 5 yr,
rather than using a small number of continually-operating sites (fewer
observational constraints) or a large number of sites, some of which may
consist almost entirely of extrapolated data. We show that the
discontinuities resulting from network changes reflect uncertainty due to a
sparse and variable network. This uncertainty effectively limits the
resolution of trends in carbon fluxes, and is a potentially significant
source of noise in assimilation systems that allow changes in observation
distribution between assimilation time steps.
The ability of the inversion to distinguish, or resolve, carbon fluxes at
various spatial scales is examined using a diagnostic known as the resolution
kernel. We find that the global partition between land and ocean fluxes is
well-resolved even for the very sparse network of the 1980's, although prior
information makes a significant contribution to the resolution. The ability
to distinguish zonal average fluxes has improved significantly since the
1980's, especially for the tropics, where the zonal ocean and land biosphere
fluxes can be distinguished. Care must be taken when interpreting zonal
average fluxes, however, since the lack of air samples for some regions in a
zone may result in a large influence from prior flux estimates for these
regions. We show that many of the TransCom 3 source regions are
distinguishable throughout the period over which estimates are produced.
Examples are Boreal and Temperate North America. The resolution of fluxes
from Europe and Australia has greatly improved since the 1990's. Other
regions, notably Tropical South America and the Equatorial Atlantic remain
practically unresolved.
Comparisons of the average seasonal cycle of the estimated carbon fluxes with
the seasonal cycle of the prior flux estimates reveals a large adjustment of
the summertime uptake of carbon for Boreal Eurasia, and an earlier onset of
springtime uptake for Temperate North America. In addition, significantly
larger seasonal cycles are obtained for some ocean regions, such as the
Northern Ocean, North Pacific, North Atlantic and Western Equatorial Pacific,
regions that appear to be well-resolved by the inversion. |
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