Spatial and temporal resolution of carbon flux estimates for 1983–2002
Open Access
- 26 May 2011
- journal article
- Published by Copernicus GmbH in Biogeosciences (online)
- Vol. 8 (5), 1309-1331
- https://doi.org/10.5194/bg-8-1309-2011
Abstract
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.Keywords
This publication has 39 references indexed in Scilit:
- Time-dependent atmospheric CO2 inversions based on interannually varying tracer transportTellus B: Chemical and Physical Meteorology, 2003
- Seasonal and interannual variability of CO2 in the equatorial PacificDeep Sea Research Part II: Topical Studies in Oceanography, 2002
- Global sea–air CO2 flux based on climatological surface ocean pCO2, and seasonal biological and temperature effectsDeep Sea Research Part II: Topical Studies in Oceanography, 2002
- KEYNOTE PERSPECTIVE. The interannual variability of the global carbon cycleTellus B: Chemical and Physical Meteorology, 1999
- Measuring the strength of ENSO events: How does 1997/98 rank?Weather, 1998
- The contribution of terrestrial sources and sinks to trends in the seasonal cycle of atmospheric carbon dioxideGlobal Biogeochemical Cycles, 1997
- A 1° × 1° distribution of carbon dioxide emissions from fossil fuel consumption and cement manufacture, 1950–1990Global Biogeochemical Cycles, 1996
- Extension and integration of atmospheric carbon dioxide data into a globally consistent measurement recordJournal of Geophysical Research: Solid Earth, 1995
- Evidence for interannual variability of the carbon cycle from the National Oceanic and Atmospheric Administration/Climate Monitoring and Diagnostics Laboratory Global Air Sampling NetworkJournal of Geophysical Research: Atmospheres, 1994
- A New Approach to Linear Filtering and Prediction ProblemsJournal of Basic Engineering, 1960