This paper documents a global Bayesian variational inversion of CO2 surface fluxes during the period 1988–2008. Weekly fluxes are estimated on a 3.75° × 2.5° (longitude‐latitude) grid throughout the ...21 years. The assimilated observations include 128 station records from three large data sets of surface CO2 mixing ratio measurements. A Monte Carlo approach rigorously quantifies the theoretical uncertainty of the inverted fluxes at various space and time scales, which is particularly important for proper interpretation of the inverted fluxes. Fluxes are evaluated indirectly against two independent CO2 vertical profile data sets constructed from aircraft measurements in the boundary layer and in the free troposphere. The skill of the inversion is evaluated by the improvement brought over a simple benchmark flux estimation based on the observed atmospheric growth rate. Our error analysis indicates that the carbon budget from the inversion should be more accurate than the a priori carbon budget by 20% to 60% for terrestrial fluxes aggregated at the scale of subcontinental regions in the Northern Hemisphere and over a year, but the inversion cannot clearly distinguish between the regional carbon budgets within a continent. On the basis of the independent observations, the inversion is seen to improve the fluxes compared to the benchmark: the atmospheric simulation of CO2 with the Bayesian inversion method is better by about 1 ppm than the benchmark in the free troposphere, despite possible systematic transport errors. The inversion achieves this improvement by changing the regional fluxes over land at the seasonal and at the interannual time scales.
We present an estimate of net ecosystem exchange (NEE) of CO₂ in Europe for the years 2001-2007. It is derived with a data assimilation that uses a large set of atmospheric CO₂ mole fraction ...observations (~70 000) to guide relatively simple descriptions of terrestrial and oceanic net exchange, while fossil fuel and fire emissions are prescribed. Weekly terrestrial sources and sinks are optimized (i.e., a flux inversion) for a set of 18 large ecosystems across Europe in which prescribed climate, weather, and surface characteristics introduce finer scale gradients. We find that the terrestrial biosphere in Europe absorbed a net average of -165 Tg C yr⁻¹ over the period considered. This uptake is predominantly in non-EU countries, and is found in the northern coniferous (-94 Tg C yr⁻¹) and mixed forests (-30 Tg C yr⁻¹) as well as the forest/field complexes of eastern Europe (-85 Tg C yr⁻¹). An optimistic uncertainty estimate derived using three biosphere models suggests the uptake to be in a range of -122 to -258 Tg C yr⁻¹, while a more conservative estimate derived from the a-posteriori covariance estimates is -165±437 Tg C yr⁻¹. Note, however, that uncertainties are hard to estimate given the nature of the system and are likely to be significantly larger than this. Interannual variability in NEE includes a reduction in uptake due to the 2003 drought followed by 3 years of more than average uptake. The largest anomaly of NEE occurred in 2005 concurrent with increased seasonal cycles of observed CO₂. We speculate these changes to result from the strong negative phase of the North Atlantic Oscillation in 2005 that lead to favorable summer growth conditions, and altered horizontal and vertical mixing in the atmosphere. All our results are available through http://www.carbontracker.eu
We present the first estimate of the global distribution of CO2 surface fluxes from 14 stations of the Total Carbon Column Observing Network (TCCON). The evaluation of this inversion is based on 1) ...comparison with the fluxes from a classical inversion of surface air-sample-measurements, and 2) comparison of CO2 mixing ratios calculated from the inverted fluxes with independent aircraft measurements made during the two years analyzed here, 2009 and 2010. The former test shows similar seasonal cycles in the northern hemisphere and consistent regional carbon budgets between inversions from the two datasets, even though the TCCON inversion appears to be less precise than the classical inversion. The latter test confirms that the TCCON inversion has improved the quality (i.e., reduced the uncertainty) of the surface fluxes compared to the assumed or prior fluxes. The consistency between the surface-air-sample-based and the TCCON-based inversions despite remaining flaws in transport models opens the possibility of increased accuracy and robustness of flux inversions based on the combination of both data sources and confirms the usefulness of space-borne monitoring of the CO2 column.
The atmospheric concentration of carbon dioxide and other greenhouse gases has been measured weekly since 1992 at the island of Lampedusa, in the Mediterranean sea. Lampedusa is a small island ...located approximately 100 km east of Tunisia, and 250 km south of Sicily. The 10‐yr CO2 data set has been analysed to quantify trends, and characterize semi‐annual, annual and inter‐annual variability. The data show an average trend of +1.7 ppmv yr−1; the average annual cycle has an amplitude of about 9 ppmv. In the period of investigation the annual growth rate varies between 0.5 and 4.5 ppmv yr−1, and the amplitude of the annual cycle between 7 and 11 ppmv yr−1. By comparing the observed growth rate with recent estimates of carbon dioxide emissions, it is calculated that 58–61% of the emitted CO2 remains in the atmosphere. The CO2 growth rate appears to be related to large‐scale dynamic phenomena, primarily El Niño/Southern Oscillation (ENSO). An evident signature of the 1997–98 El Niño is apparent in the CO2 record, and corresponds to a weakening of the exchange with the biosphere. A high correlation between the global average temperature and the 12‐month average carbon dioxide growth rate is also found. Wind direction displays a significant inter‐annual variability throughout the measurement period, possibly influencing the observed evolution of the CO2 concentration.
We present the first estimate of the global distribution of CO2surface fluxes from 14 stations of the Total Carbon Column Observing Network (TCCON). The evaluation of this inversion is based on 1) ...comparison with the fluxes from a classical inversion of surface air‐sample‐measurements, and 2) comparison of CO2mixing ratios calculated from the inverted fluxes with independent aircraft measurements made during the two years analyzed here, 2009 and 2010. The former test shows similar seasonal cycles in the northern hemisphere and consistent regional carbon budgets between inversions from the two datasets, even though the TCCON inversion appears to be less precise than the classical inversion. The latter test confirms that the TCCON inversion has improved the quality (i.e., reduced the uncertainty) of the surface fluxes compared to the assumed or prior fluxes. The consistency between the surface‐air‐sample‐based and the TCCON‐based inversions despite remaining flaws in transport models opens the possibility of increased accuracy and robustness of flux inversions based on the combination of both data sources and confirms the usefulness of space‐borne monitoring of the CO2 column.
Key Points
Consistent seasonal cycle inferred from XCO2 and from pointwise observations
The TCCON inversion improves the quality of the prior fluxes
Our study experimentally confirms the usefulness of space‐borne CO2 monitoring
This paper documents a global Bayesian variational inversion of CO
2
surface fluxes during the period 1988–2008. Weekly fluxes are estimated on a 3.75° × 2.5° (longitude‐latitude) grid throughout the ...21 years. The assimilated observations include 128 station records from three large data sets of surface CO
2
mixing ratio measurements. A Monte Carlo approach rigorously quantifies the theoretical uncertainty of the inverted fluxes at various space and time scales, which is particularly important for proper interpretation of the inverted fluxes. Fluxes are evaluated indirectly against two independent CO
2
vertical profile data sets constructed from aircraft measurements in the boundary layer and in the free troposphere. The skill of the inversion is evaluated by the improvement brought over a simple benchmark flux estimation based on the observed atmospheric growth rate. Our error analysis indicates that the carbon budget from the inversion should be more accurate than the a priori carbon budget by 20% to 60% for terrestrial fluxes aggregated at the scale of subcontinental regions in the Northern Hemisphere and over a year, but the inversion cannot clearly distinguish between the regional carbon budgets within a continent. On the basis of the independent observations, the inversion is seen to improve the fluxes compared to the benchmark: the atmospheric simulation of CO
2
with the Bayesian inversion method is better by about 1 ppm than the benchmark in the free troposphere, despite possible systematic transport errors. The inversion achieves this improvement by changing the regional fluxes over land at the seasonal and at the interannual time scales.
ABSTRACT
The first 4 years (1994–1997) of continuous atmospheric CO2 measurements from Jubany station located on the Antarctic peninsula are presented. Details are given on the station environment, ...meteorological conditions, instrumentation, and data selection strategy. The average seasonal cycle and annual growth rate are characterized and compared with other independent Antarctic CO2 measurement records. An analysis of diurnal behaviour and local meteorology and statistical variability in the measurements suggests that Jubany is a suitable site for making systematic observations of CO2 that are representative of large well‐mixed air masses.
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