TransCom 3 CO2 inversion intercomparison: 1. Annual mean control results and sensitivity to transport and prior flux information (original) (raw)
Related papers
Journal of Geophysical Research, 1999
The inversion of atmospheric transport of CO 2 may potentially be a means for monitoring compliance with emission treaties in the future. There are two types of errors, though, which may cause errors in inversions: (1) amplification of high-frequency data variability given the information loss in the atmosphere by mixing and (2) systematic errors in the CO 2 flux estimates caused by various approximations used to formulate the inversions. In this study we use simulations with atmospheric transport models and a time independent inverse scheme to estimate these errors as a function of network size and the number of flux regions solved for. Our main results are as follows. When solving for 10 -20 source regions, the average uncertainty of flux estimates caused by amplification of high-frequency data variability alone decreases strongly with increasing number of stations for up to ϳ150 randomly positioned stations and then levels off (for 150 stations of the order of Ϯ0.2 Pg C yr Ϫ1 ). As a rule of thumb, about 10 observing stations are needed per region to be estimated.
Influence of transport uncertainty on annual mean and seasonal inversions of atmospheric CO 2 data
Journal of Geophysical Research, 2002
1] Inversion methods are often used to estimate surface CO 2 fluxes from atmospheric CO 2 concentration measurements, given an atmospheric transport model to relate the two. The published estimates disagree strongly on the location of the main sources and sinks, however. Are these differences due to the different time spans considered, or are they artifacts of the method and data used? Here we assess the uncertainty in such estimates due to the choice of time discretization of the measurements and fluxes, the spatial resolution of the fluxes, and the transport model. A suite of 27 Bayesian least squares inversions has been run, given by varying the number of flux regions solved for (7, 12, and 17), the time discretization (annual/annual, annual/monthly, and monthly/monthly for the fluxes/data), and the transport model (TM2, TM3, and GCTM), while holding all other inversion details constant. The estimated fluxes from this ensemble of inversions for the land + ocean sum are stable over large zonal bands, but the spread in the results increases when considering the longitudinal flux distribution inside these bands. On average for 1990-1994 the inversions place a large CO 2 uptake north of 30°N (3.2 ± 0.3 GtC yr À1 ), mostly over the land regions, with more in Eurasia than North America. The ocean fluxes are generally smaller than given by , especially south of 15°S and in the global total, where they are less than half as large. A small uptake is found for the tropical land regions, suggesting that growth more than compensates for deforestation there. The results for the different transport models are consistent with their known mixing properties; the longitudinal pattern of their land biosphere rectifier, in particular, strongly influences the regional partitioning of the flux in the north. While differences between the transport models contribute significantly to the spread of the results, an equivalent or even larger spread is due to the time discretization method used: Solving for annual mean fluxes with monthly mean measurements tended to give spurious land/ocean flux partition in the north. We suggest then that this time discretization method be avoided. Overall, the uncertainty quoted for the estimated fluxes should include not only the random error calculated by the inversion equations but also all the systematic errors in the problem, such as those addressed in this study.
Global Biogeochemical Cycles, 2006
1] Monthly CO 2 fluxes are estimated across 1988-2003 for 22 emission regions using data from 78 CO 2 measurement sites. The same inversion (method, priors, data) is performed with 13 different atmospheric transport models, and the spread in the results is taken as a measure of transport model error. Interannual variability (IAV) in the winds is not modeled, so any IAV in the measurements is attributed to IAV in the fluxes. When both this transport error and the random estimation errors are considered, the flux IAV obtained is statistically significant at P 0.05 when the fluxes are grouped into land and ocean components for three broad latitude bands, but is much less so when grouped into continents and basins. The transport errors have the largest impact in the extratropical northern latitudes. A third of the 22 emission regions have significant IAV, including the Tropical East Pacific (with physically plausible uptake/release across the 1997-2000 El Niño/La Niña) and Tropical Asia (with strong release in 1997/1998 coinciding with large-scale fires there). Most of the global IAV is attributed robustly to the tropical/southern land biosphere, including both the large release during the 1997/1998 El Niño and the post-Pinatubo uptake.
Atmospheric Chemistry and Physics, 2013
The Bayesian framework of CO 2 flux inversions permits estimates of the retrieved flux uncertainties. Here, the reliability of these theoretical estimates is studied through a comparison against the misfits between the inverted fluxes and independent measurements of the CO 2 Net Ecosystem Exchange (NEE) made by the eddy covariance technique at local (few hectares) scale. Regional inversions at 0.5 • resolution are applied for the western European domain where ∼ 50 eddy covariance sites are operated. These inversions are conducted for the period 2002-2007. They use a mesoscale atmospheric transport model, a prior estimate of the NEE from a terrestrial ecosystem model and rely on the variational assimilation of in situ continuous measurements of CO 2 atmospheric mole fractions. Averaged over monthly periods and over the whole domain, the misfits are in good agreement with the theoretical uncertainties for prior and inverted NEE, and pass the chi-square test for the variance at the 30 % and Published by Copernicus Publications on behalf of the European Geosciences Union. 9040 G. Broquet et al.: Reliability of uncertainties from the inversion of CO 2 NEE European continent likely ends later than represented by the prior ecosystem model.
Global Biogeochemical Cycles, 2005
1] Recent inverse analyses constraining carbon fluxes using atmospheric CO 2 observations have assumed that the CO 2 source from atmospheric oxidation of reduced carbon is released at the surface rather than distributed globally in the atmosphere. This produces a bias in the estimates of surface fluxes. We used a three-dimensional (3D) atmospheric chemistry model (GEOS-CHEM) to evaluate the magnitude of this effect on modeled concentrations and flux estimates. We find that resolving the 3D structure of the atmospheric CO 2 source, as opposed to emitting this reduced carbon as CO 2 at the surface, yields a decrease in the modeled annual mean interhemispheric gradient (N-S) of 0.21 ppm. Larger adjustments (up to À0.6 ppm) are apparent on a regional basis in and downwind of regions of high reduced carbon emissions. We used TransCom3 annual mean simulations from three transport models to evaluate the implications for inversion estimates. The main impacts are systematic decreases in estimates of northern continental land uptake (i.e., by 0.22 to 0.26 Pg C yr À1 ), and reductions in tropical land carbon efflux with smaller changes over oceans and in the Southern Hemisphere. These adjustments represent a systematic bias in flux estimates, accounting for changes of 9 to 27% in the estimated northern land CO 2 sink for the three models evaluated here. Our results highlight the need for a realistic description of reduced carbon emission and oxidation processes in deriving inversion estimates of CO 2 surface fluxes. Citation: Suntharalingam, P., J. T. Randerson, N. Krakauer, J. A. Logan, and D. J. Jacob (2005), Influence of reduced carbon emissions and oxidation on the distribution of atmospheric CO 2 : Implications for inversion analyses, Global Biogeochem. Cycles, 19, GB4003,
Global Biogeochemical Cycles, 2005
1] Recent inverse analyses constraining carbon fluxes using atmospheric CO 2 observations have assumed that the CO 2 source from atmospheric oxidation of reduced carbon is released at the surface rather than distributed globally in the atmosphere. This produces a bias in the estimates of surface fluxes. We used a three-dimensional (3D) atmospheric chemistry model (GEOS-CHEM) to evaluate the magnitude of this effect on modeled concentrations and flux estimates. We find that resolving the 3D structure of the atmospheric CO 2 source, as opposed to emitting this reduced carbon as CO 2 at the surface, yields a decrease in the modeled annual mean interhemispheric gradient (N-S) of 0.21 ppm. Larger adjustments (up to À0.6 ppm) are apparent on a regional basis in and downwind of regions of high reduced carbon emissions. We used TransCom3 annual mean simulations from three transport models to evaluate the implications for inversion estimates. The main impacts are systematic decreases in estimates of northern continental land uptake (i.e., by 0.22 to 0.26 Pg C yr À1 ), and reductions in tropical land carbon efflux with smaller changes over oceans and in the Southern Hemisphere. These adjustments represent a systematic bias in flux estimates, accounting for changes of 9 to 27% in the estimated northern land CO 2 sink for the three models evaluated here. Our results highlight the need for a realistic description of reduced carbon emission and oxidation processes in deriving inversion estimates of CO 2 surface fluxes. Citation: Suntharalingam, P., J. T. Randerson, N. Krakauer, J. A. Logan, and D. J. Jacob (2005), Influence of reduced carbon emissions and oxidation on the distribution of atmospheric CO 2 : Implications for inversion analyses, Global Biogeochem. Cycles, 19, GB4003,
Time-dependent atmospheric CO2 inversions based on interannually varying tracer transport
Tellus B, 2003
The use of inverse calculations to estimate surface CO 2 fluxes from atmospheric concentration measurements has gained large attention in recent years. The success of an inversion will, among other factors, depend strongly on how realistically atmospheric tracer transport is represented by the employed transport model, as it links surface CO 2 fluxes to modelled concentrations at the location of measurement stations. We present sensitivity studies demonstrating that transport modelling should be based on interannually varying meteorology, as compared to the traditional use of repeating a single year's winds only. Moreover, we propose an improved procedure of representing the concentration sampling in the model, which allows consistency with the measurements and uses their information content more efficiently. In further sensitivity tests, we estimate the effect of different spatial transport model resolutions and different meteorological driver data sets. Finally, we assess the quality of the inversion results with the help of independent measurements and flux estimates, and preliminarily discuss some of the resulting features.
European CO2 fluxes from atmospheric inversions using regional and global transport models
Climatic Change, 2010
Approximately half of human-induced carbon dioxide (CO 2 ) emissions are taken up by the land and ocean, and the rest stays in the atmosphere, increasing the global concentration and acting as a major greenhouse-gas (GHG) climate-forcing element. Although GHG mitigation is now in the political arena, the exact spatial distribution of the land sink is not well known. In this paper, an estimation of mean European net ecosystem exchange (NEE) carbon fluxes for the period 1998-2001 is performed with three mesoscale and two global transport models, based on the integration of atmospheric CO 2 measurements into the same Bayesian synthesis inverse approach. A special focus is given to sub-continental regions of Europe making use of newly available CO 2 concentration measurements in this region. Inverse flux estimates from the five transport models are compared with independent flux estimates from four ecosystem models. All inversions detect a strong annual Climatic Change carbon sink in the southwestern part of Europe and a source in the northeastern part. Such a dipole, although robust with respect to the network of stations used, remains uncertain and still to be confirmed with independent estimates. Comparison of the seasonal variations of the inversion-based net land biosphere fluxes (NEP) with the NEP predicted by the ecosystem models indicates a shift of the maximum uptake period, from June in the ecosystem models to July in the inversions. This study thus improves on the understanding of the carbon cycle at sub-continental scales over Europe, demonstrating that the methodology for understanding regional carbon cycle is advancing, which increases its relevance in terms of issues related to regional mitigation policies.
Inverse modeling of annual atmospheric CO2sources and sinks: 1. Method and control inversion
Journal of Geophysical Research: Atmospheres, 1999
A primary goal of developing the CO2 atmospheric measurement network is to better characterize the sources and sinks of atmospheric CO2. Atmospheric transport models can be used to interpret atmospheric measurements in terms of surface fluxes using inverse methodology. In this paper we present a three-dimensional (3-D) inversion of CO2 measurements in order to infer annual sources and sinks of CO2 at a continental scale (continents and ocean basins) for a climatological year representing the 1985-1995 period. Solving this inverse problem requires (1) a data space representing monthly CO2 measurements, here at 77 sites (surface, ships, planes), (2) a flux space describing a priori fluxes between carbon reservoirs, and (3) a 3-D transport model linking the flux space to the data space. Knowledge of these three elements, together with their associated errors, allows one to reduce the uncertainties of the CO2 sources and sinks. In the 1985-1995 period, for our control inversion, the global continental sink is found to be 2.7+ 1.5 Gt C yr i for an optimized deforestation source of 1.4+0.6 Gt C yr 1 , yielding a net land uptake of 1.3+ 1.6 Gt C yr 1 (fossil fuel removed). The continental partition of this budget is (in units of Gt C yrl): Arctic +0.2+0.3, North America-0.5+0.6, Europe-0.3+0.8, north Asia-1.5+0.7, tropics (except Asia) +0.3+0.9, tropical Asia +0.8+0.4, and Southern Hemisphere-0.1 +0.3. The inferred partition for the controversial Northern Hemisphere CO2 sink reveals that a major sink is located over the north Asia continent. For oceans we find a net global sink of 1.5+0.5 Gt C yr 1 with the following partition