ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-12-337-2012 Constraining the CO<sub>2</sub> budget of the corn belt: exploring uncertainties from the assumptions in a mesoscale inverse system Lauvaux T. 1 Schuh A. E. 2 5 Uliasz M. 5 Richardson S. 1 Miles N. 1 Andrews A. E. 4 Sweeney C. 4 Diaz L. I. 1 Martins D. 1 Shepson P. B. 3 Davis K. J. 1 Department of Meteorology, The Pennsylvania State University, Inversity Park, Pennsylvania, USA NREL, Fort Collins, Colorado, USA Purdue University, W. Lafayette, Indiana, USA National Oceanic and Atmospheric Association, ESRL/GMD, Boulder, Colorado, USA Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado, USA 05 01 2012 12 1 337 354 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/12/337/2012/acp-12-337-2012.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/12/337/2012/acp-12-337-2012.pdf

We performed an atmospheric inversion of the CO<sub>2</sub> fluxes over Iowa and the surrounding states, from June to December 2007, at 20 km resolution and weekly timescale. Eight concentration towers were used to constrain the carbon balance in a 1000×1000 km<sup>2</sup> domain in this agricultural region of the US upper midwest. The CO<sub>2</sub> concentrations of the boundaries derived from CarbonTracker were adjusted to match direct observations from aircraft profiles around the domain. The regional carbon balance ends up with a sink of 183 Tg C±35 Tg C over the area for the period June–December, 2007. Potential bias from incorrect boundary conditions of about 0.55 ppm over the 7 months was corrected using mixing ratios from four different aircraft profile sites operated at a weekly time scale, acting as an additional source of uncertainty of 24 Tg C. We used two different prior flux estimates, the SiBCrop model and the inverse flux product from the CarbonTracker system. We show that inverse flux estimates using both priors converge to similar posterior estimates (20 Tg C difference), in our reference inversion, but some spatial structures from the prior fluxes remain in the posterior fluxes, revealing the importance of the prior flux resolution and distribution despite the large amount of atmospheric data available. The retrieved fluxes were compared to eddy flux towers in the corn and grassland areas, revealing an improvement in the seasonal cycles between the two compared to the prior fluxes, despite large absolute differences due to representation errors. The uncertainty of 34 Tg C (or 34 g C m<sup>2</sup>) was derived from the posterior uncertainty obtained with our reference inversion of about 25 to 30 Tg C and from sensitivity tests of the assumptions made in the inverse system, for a mean carbon balance over the region of −183 Tg C, slightly weaker than the reference. Because of the potential large bias (~24 Tg C in this case) due to choice of background conditions, proportional to the surface but not to the regional flux, this methodology seems limited to regions with a large signal (sink or source), unless additional observations can be used to constrain the boundary inflow.

 References Ahmadov, R., Gerbig, C., Kretschmer, R., Koerner, S., Neininger, B., Dolman, A J., and Sarrat, C.: Mesoscale covariance of transport and CO<sub>2</sub> fluxes: Evidence from observations and simulations using the WRF-VPRM coupled atmosphere-biosphere model, J. Geophys. Res., 112, D22107, http://dx.doi.org/10.1029/2007JD008552doi:10.1029/2007JD008552, 2007. Baker, D F., Law, R M., Gurney, K R., Rayner, P., Peylin, P., Denning, A S., Bousquet, P., Bruhwiler, L., Chen, Y.-H., Ciais, P., Fung, I Y., Heimann, M., John, J., Maki, T., Maksyutov, S., Masarie, K., Prather, M., Pak, B., Taguchi, S., , and Zhu, Z.: TransCom 3 inversion intercomparison: Impact of transport model errors on the interannual variability of regional CO<sub>2</sub> fluxes, 1988–2003, Global Biogeochem. Cy., 20, 439, http://dx.doi.org/10.1029/2004GB002doi:10.1029/2004GB002, 2007. Baker, J. and Griffis, T.: Examining strategies to improve the carbon balance of corn/soybean agriculture using eddy covariance and mass balance techniques, Agri. Forest Meteorol., 128, 163–177, http://dx.doi.org/10.1016/j.agrformet.2004.11.005doi:10.1016/j.agrformet.2004.11.005, 2004. Bousquet, P., Peylin, P., Ciais, P., Quéré, C L., Friedlingstein, P., and Tans, P P.: Regional changes in carbon dioxide fluxes of land and oceans since 1980, Science, 290, 1342–1346, 2000. Butler, M P., Davis, K J., Denning, A S., and Kawa, S R.: Using continental observations in global atmospheric inversions of CO<sub>2</sub>: North American carbon sources and sinks, Tellus B, 62, 550–572, http://dx.doi.org/10.1111/j.1600-0889.2010.00501.xdoi:10.1111/j.1600-0889.2010.00501.x, 2010. Canadell, J G., Le~Quéré, C., Raupach, M R., Field, C B., Buitenhuis, E T., Ciais, P., Conway, T J., Gillett, N P., Houghton, R A., and Marland, G.: Contributions to accelerating atmospheric CO<sub>2</sub> growth from economic activity, carbon intensity, and efficiency of natural sinks, Proc. Natl. Acad. Sci., 104, 18866–18870, http://dx.doi.org/10.1073/pnas.0702737104doi:10.1073/pnas.0702737104, 2007. Carouge, C., Rayner, P J., Peylin, P., Bousquet, P., Chevallier, F., and Ciais, P.: What can we learn from European continuous atmospheric CO<sub>2</sub> measurements to quantify regional fluxes – Part 2: Sensitivity of flux accuracy to inverse setup, Atmos. Chem. Phys., 10, 3119–3129, http://dx.doi.org/10.5194/acp-10-3119-2010doi:10.5194/acp-10-3119-2010, 2010. Chen, F. and Dudhia, J.: Coupling an advanced land surface-hydrology model with the PennState-NCAR MM5 modelling system. Part1: model implementation and sensitivity, Mon. Weather Rev., 129, 569–585, 2001. Chevallier, F., Viovy, N., Reichstein, M., and Ciais, P.: On the assignment of prior errors in Bayesian inversions of CO<sub>2</sub> surface fluxes, Geophys. Res. Let., 33, L13802, http://dx.doi.org/10.1029/2006GL026496doi:10.1029/2006GL026496, 2006. Chevallier, F., Ciais, P., Conway, T J., Aalto, T., Anderson, B E., Bousquet, P., Brunke, E G., Ciattaglia, L., Esaki, Y., Frohlich, M., Gomez, A., Gomez-Palaez, A J., Haszpra, L., Krummel, P B., Langenfelds, R., Leuenberger, M., Machida, T., Maignan, F., Matsueda, H., Morgui, J A., Mukai, H., Nakazawa, T., Peylin, P., Ramonet, M., Rivier, L., Sawa, Y., Schmidt, M., Steele, P., Vay, S A., Vermeulen, A T., Wofsy, S C., and Worthy, D.: CO<sub>2</sub> surface fluxes at grid point scale estimated from a global 21-year reanalysis of atmospheric measurements, J. Geophys. Res., http://dx.doi.org/10.1029/2010JD013887doi:10.1029/2010JD013887, in press, 2010. Corbin, K D., Denning, A S., Lokupitiya, E Y., Schuh, A E., Miles, N L., , Davis, K J., Richardson, S., and Baker, I T.: Assessing the impact of crops on regional CO<sub>2</sub> fluxes and atmospheric concentrations, Tellus B, 62, 521–532, http://dx.doi.org/10.1111/j.1600-0889.2010.00485.xdoi:10.1111/j.1600-0889.2010.00485.x, 2008. Crosson, E R.: A cavity ring-down analyzer for measuring atmospheric levels of methane, carbon dioxide, and water vapor, Appl. Phys. B, 92, 403–408, 2008. Dolman, A J., Noilhan, J., Durand, P., Sarrat, C., Brut, A., Piguet, B., Butet, A., Jarosz, N., Brunet, Y., Loustau, D., Lamaud, E., Tolk, L., Miglietta, R. R F., Gioli, B., Magliulo, V., Esposito, M., Gerbig, C., Körner, S., Galdemard, P., Ramonet, M., Ciais, P., Neininger, B., Hutjes, R. W A., Macatangay, J. A. E R., Schrems, O., Pérez-Landa, G., Sanz, M J., Scholz, Y., Facon, G., Ceschia, E., and Beziat, P.: CERES, the CarboEurope Regional Experiment Strategy in Les Landes, South West France, May–June 2005, Bull. Am. Meteorol. Soc., 87, 1367–1379, http://dx.doi.org/10.1175/BAMS-87-10-1367doi:10.1175/BAMS-87-10-1367, 2006. Enting, I G.: Inverse Problems in Atmospheric Constituent Transport, Cambridge University Press, Cambridge, UK, 412 pp., 2002. Francey, R J., Tans, P P., Allison, C E., Enting, I G., White, J. W C., and Trolier, M.: Changes in oceanic and terrestrial carbon uptake since 1982, Nature, 373, 326–330, 1995. Garman, K., Hill, K A., Wyss, P., Carlsen, M., Zimmerman, J R., Stirm, B H., Carney, T Q., Santini, R., and Shepson, P B.: An airborne and wind tunnel evaluation of a wind turbulence measurement system for aircraft-based flux measurements, J. Atmos. Ocean. Technol., 23, 1696–1708, 2006. Geels, C., Gloor, M., Ciais, P., Bousquet, P., Peylin, P., Vermeulen, A T., Dargaville, R., Aalto, T., Brandt, J., Christensen, J H., Frohn, L M., Haszpra, L., Karstens, U., Rödenbeck, C., Ramonet, M., Carboni, G., and Santaguida, R.: Comparing atmospheric transport models for future regional inversions over Europe; Part~1: mapping the atmospheric CO<sub>2</sub> signals, Atmos. Chem. Phys., 7, 3461–3479, 2007. Gerbig, C., Lin, J C., Wofsy, S C., Daube, B C., Andrews, A E., Stephens, B B., Bakwin, P S., and Grainger, C A.: Toward constraining regional-scale fluxes of $CO_2$ with atmospheric observations over a continent: 1. Observed spatial variability from airborne platforms, J. Geophys. Res., 108, 4756, http://dx.doi.org/10.1029/2002JD003018doi:10.1029/2002JD003018, 2003a. Gerbig, C., Lin, J C., Wofsy, S C., Daube, B C., Andrews, A E., Stephens, B B., Bakwin, P S., and Grainger, C A.: Toward constraining regional-scale fluxes of $CO_2$ with atmospheric observations over a continent: 2. Analysis of COBRA data using a receptor-oriented framework, J. Geophys. Res., 108, 4757, http://dx.doi.org/10.1029/2003JD003770doi:10.1029/2003JD003770, 2003b. Gerbig, C., Lin, J. C., Munger, J. W., and Wofsy, S. C.: What can tracer observations in the continental boundary layer tell us about surface-atmosphere fluxes?, Atmos. Chem. Phys., 6, 539–554, http://dx.doi.org/10.5194/acp-6-539-2006doi:10.5194/acp-6-539-2006, 2006. Gioli, B., Miglietta, F., Martino, B D., Hutjes, R., Dolman, H., Lindroth, A., Schumacher, M., Sanz, M J., Manca, G., Peressotti, A., and Dumas, E J.: Comparison between tower and aircraft-based eddy covariance fluxes in five European regions, Agr. Forest Meteorol., 127, 1–16, 2004. Göckede, M., Michalak, A M., Vickers, D., Turner, D P., and Law, B E.: Atmospheric inverse modeling to constrain regional scale CO<sub>2</sub> budgets at high spatial and temporal resolution, J. Geophys. Res., 115, D15113, http://dx.doi.org/10.1029/2009JD012257doi:10.1029/2009JD012257, 2010a. Göckede, M., Turner, D P., Michalak, A M., Vickers, D., and Law, B E.: Sensitivity of a subregional scale atmospheric inverse CO<sub>2</sub> modeling framework to boundary conditions, J. Geophys. Res., 115, D24112, http://dx.doi.org/10.1029/2010JD014443doi:10.1029/2010JD014443, 2010b. Gourdji, S M., Hirsch, A I., Mueller, K L., Yadav, V., Andrews, A E., and Michalak, A M.: Regional-scale geostatistical inverse modeling of North American CO<sub>2</sub> fluxes: a synthetic data study, Atmos. Chem. Phys., 10, 6151–6167, http://dx.doi.org/10.5194/acp-10-6151-2010doi:10.5194/acp-10-6151-2010, 2010. Grabon, J S., Davis, K J., Kiemle, C., and Ehret, G.: Airborne Lidar observations of the transition zone between the convective boundary layer and free atmosphere during the international H<sub>2</sub>O Project (IHOP) in 2002, Bound.-Layer Meteorol., 134, 61–83, 2010. Griffis, T J., Baker, J M., Sargent, S D., Erickson, M., Corcoran, J., Chen, M., and Billmark, K.: Influence of C<sub>4</sub> vegetation on $^13CO_2$ discrimination and isoforcing in the upper Midwest, United State, Global Biogeochem. Cy., 24, GB4006, http://dx.doi.org/10.1029/2009GB003768doi:10.1029/2009GB003768, 2010. Gu, L., Meyers, T., Pallardy, S. G., Hanson, P., Yang, B., Heuer, M., Hosman, K. P., Riggs, J. S., Sluss, D., and Wullschleger, S.D.: Direct and indirect effects of atmospheric conditions and soil moistre on surface energy partitioning revealed by a prolonged drought at a temperate forest site, J. Geophys. Res., 111, D16102, http://dx.doi.org/10.1029/2006JD007161doi:10.1029/2006JD007161, 2006. Gurney, K R., Law, R M., Denning, A S., Rayner, P J., Baker, D., Bousquet, P., Bruhwiler, L., Chen, Y.-H., Ciais, P., Fan, S., Fung, I Y., Gloor, M., Heimann, M., Higuchi, K., John, J., Maki, T., Maksyutov, S., Masarie, K., Peylin, P., Prather, M., Pak, B C., Randerson, J., Sarmiento, J., Taguchi, S., Takahashi, T., and Yuen, C.-W.: Towards robust regional estimates of CO<sub>2</sub> sources and sinks using atmospheric transport models, Nature, 415, 626–630, 2002. Kaminski, T., Rayner, P J., Heimann, M., and Enting, I G.: On Aggregation Errors in Atmospheric Transport Inversions, J. Geophys. Res., 106, 4703–4715, 2001. Krol, M., Houweling, S., Bregman, B., van~den Broek, M., Segers, A., van Velthoven, P., Peters, W., Dentener, F., and Bergamaschi, P.: The two-way nested global chemistry-transport zoom model TM5: algorithm and applications, Atmos. Chem. Phys., 5, 417–432, http://dx.doi.org/10.5194/acp-5-417-2005doi:10.5194/acp-5-417-2005, 2005. Lauvaux, T., Uliasz, M., Sarrat, C., Chevallier, F., Bousquet, P., Lac, C., Davis, K J., Ciais, P., Denning, A S., and Rayner, P J.: Mesoscale inversion: first results from the CERES campaign with synthetic data, Atmos. Chem. Phys., 8, 3459–3471, http://dx.doi.org/10.5194/acp-8-3459-2008doi:10.5194/acp-8-3459-2008, 2008. Lauvaux, T., Gioli, B., Sarrat, C., Rayner, P J., Ciais, P., Chevallier, F., Noilhan, J., Miglietta, F., Brunet, Y., Ceschia, E., Dolman, H., Elbers, J A., Gerbig, C., Hutjes, R., Jarosz, N., Legain, D., and Uliasz, M.: Bridging the gap between atmospheric concentrations and local ecosystem measurements, Geophys. Res. Lett., 36, L19809, http://dx.doi.org/10.1029/2009GL039574doi:10.1029/2009GL039574, 2009a. Lauvaux, T., Pannekoucke, O., Sarrat, C., Chevallier, F., Ciais, P., Noilhan, J., and Rayner, P J.: Structure of the transport uncertainty in mesoscale inversions of CO<sub>2</sub> sources and sinks using ensemble model simulations, Biogeosciences, 6, 1089–1102, http://dx.doi.org/10.5194/bg-6-1089-2009doi:10.5194/bg-6-1089-2009, 2009b. Law, R M., Rayner, P J., Steele, L P., and Enting, I G.: Data and modelling requirements for CO<sub>2</sub> inversions using high frequency data, Tellus, 55B, 512–521, http://dx.doi.org/10.1034/j.1600-0560.2003.0029.xdoi:10.1034/j.1600-0560.2003.0029.x, 2003. Lokupitiya, E., Denning, S., Paustian, K., Baker, I., Schaefer, K., Verma, S., Meyers, T., Bernacchi, C J., Suyker, A., and Fischer, M.: Incorporation of crop phenology in Simple Biosphere Model (SiBcrop) to improve land-atmosphere carbon exchanges from croplands, Biogeosciences, 6, 969–986, http://dx.doi.org/10.5194/bg-6-969-2009doi:10.5194/bg-6-969-2009, 2009. Martins, D K., Sweeney, C., Stirm, B H., and Shepson, P B.: Regional surface flux of CO<sub>2</sub> inferred from changes in the advected CO<sub>2</sub> column density, Agric. For. Meteorol., 149, 1674–1685, http://dx.doi.org/10.1016/j.agrformet.2009.05.005doi:10.1016/j.agrformet.2009.05.005, 2009. Matamala, R., Jastrow, D., Miller, R., and Garten, C.: Temporal changes in the distribution of C and N stocks in a restored tallgrass prairie in the U.S. Midwest, Ecol. Appl., 18, 1470–1488, 2008. Meyers, T. and Hollinger, S.: An assessment of storage terms in the surface energy balance of maize and soybean, Agr. Forest Meteorol., 125, 105–115, 2004. Miles, N. L., Richardson, S. J., Davis, K. J., Lauvaux, T., Andrews, A. E., West, T. O., Bandaru, V., and Crosson, E. R.: Large amplitude spatial and temporal gradients in atmospheric boundary layer CO2 mole fractions detected with a tower-based network in the U.S. Upper Midwest, J. Geophys. Res., accepted, 2011. Nakanishi, M. and Niino, H.: An improved Mellor-Yamada level 3 model with condensation physics, Bound. Layer Meteorol., 111, 1–31, 2004. Ogle, S., Davis, K., Andrews, A., Gurney, K., West, T., Cook, R., Parkin, R., Morisette, J., Verma, S., and Wofsy, S.: Science plan: Mid-Continent Intensive campaign of the North American Carbon Program, US Global Change Carbon Program – North American Carbon Program, available online at: http://www.nacarbon.org/nacp/mci.html, 2006. Pérez-Landa, G., Ciais, P., Sanz, M J., Gioli, B., Miglietta, F., Palau, J L., Gangoiti, G., and Millán, M M.: Mesoscale circulations over complex terrain in the Valencia coastal region, Spain – Part 1: Simulation of diurnal circulation regimes, Atmos. Chem. Phys., 7, 1835–1849, http://dx.doi.org/10.5194/acp-7-1835-2007doi:10.5194/acp-7-1835-2007, 2007. Peters, W., Jacobson, A R., Sweeney, C., Andrews, A E., Conway, T J., Masarie, K., Miller, J B., Bruhwiler, L. M P., Pétron, G., Hirsch, A I., Worthy, D. E J., van~der Werf, G R., Randerson, J T., Wennberg, P O., Krol, M C., and Tans, P P.: An atmospheric perspective on North American carbon dioxide exchange: CarbonTracker, Proc. Natl. Acad. Sci., 104, 18925–18930, http://dx.doi.org/10.1073/pnas.0708986104doi:10.1073/pnas.0708986104, 2007. Peylin, P., Rayner, P J., Bousquet, P., Carouge, C., Hourdin, F., Ciais, P., Heinrich, P., and AeroCarb Contributors: Daily CO<sub>2</sub> flux estimate over Europe from continuous atmospheric measurements – Part 1 inverse methodology, Atmos. Chem. Phys., 5, 3173–3186, http://dx.doi.org/10.5194/acp-5-3173-2005doi:10.5194/acp-5-3173-2005, 2005. Richardson, S. J., Miles, N. L., Davis, K. J., Crosson, E. R., Rella, C., and Andrews, A. E.: Field testing of cavity ring-down spectroscopy analyzers measuring carbon dioxide and water vapor, J. Atmos. Oceanic Technol., 0739–0572, http://dx.doi.org/10.1175/JTECH-D-11-00063.1doi:10.1175/JTECH-D-11-00063.1, 2011. Rödenbeck, C., Gerbig, C., Trusilova, K., and Heimann, M.: A two-step scheme for high-resolution regional atmospheric trace gas inversions based on independent models, Atmos. Chem. Phys., 9, 5331–5342, http://dx.doi.org/10.5194/acp-9-5331-2009doi:10.5194/acp-9-5331-2009, 2009. Sarrat, C., Noilhan, J., Dolman, A J., Gerbig, C., Ahmadov, R., Tolk, L F., Meesters, A. G. C A., Hutjes, R. W A., Ter~Maat, H W., Pérez-Landa, G., and Donier, S.: Atmospheric CO<sub>2</sub> modeling at the regional scale: an intercomparison of 5 meso-scale atmospheric models, Biogeosciences, 4, 1115–1126, http://dx.doi.org/10.5194/bg-4-1115-2007doi:10.5194/bg-4-1115-2007, 2007a. Sarrat, C., Noilhan, J., Lacarr\`re, P., Donier, S., Lac, C., Calvet, J C., Dolman, A J., Gerbig, C., Neininger, B., Ciais, P., Paris, J D., Boumard, F., Ramonet, M., and Butet, A.: Atmospheric CO<sub>2</sub> modeling at the regional scale: Application to the CarboEurope Regional Experiment, J. Geophys. Res., 112, D12105, http://dx.doi.org/10.1029/2006JD008107doi:10.1029/2006JD008107, 2007b. Schuh, A E., Denning, A S., Corbin, K D., Baker, I T., Uliasz, M., Parazoo, N., Andrews, A E., and Worthy, D. E J.: A regional high-resolution carbon flux inversion of North America for 2004, Biogeosciences, 7, 1625–1644, http://dx.doi.org/10.5194/bg-7-1625-2010doi:10.5194/bg-7-1625-2010, 2010. Skamarock, W C., Klemp, J B., Dudhia, J., Gill, D O., Barker, D M., Wang, W., and Powers, J G.: A Description of the Advanced Research WRF Version 2, National Center of Atmospheric Research, Boulder, CO, USA, 100 pp., 2005. Stephens, B B., Gurney, K R., Tans, P P., Sweeney, C., Peters, W., Bruhwiler, L., Ciais, P., Ramonet, M., Bousquet, P., Nakazawa, T., Aoki, S., Machida, T., Inoue, G., Vinnichenko, N., Lloyd, J., Jordan, A., Heimann, M., Shibistova, O., Langenfelds, R L., Steele, L P., Francey, R J., and Denning, A S.: Weak Northern and Strong Tropical Land Carbon Uptake from Vertical Profiles of Atmospheric CO<sub>2</sub>, Science, 316, 1732–1735, http://dx.doi.org/10.1126/science.1137004doi:10.1126/science.1137004, 2007. Sweeney, C., Karion, A., Wolter, S., Neff, D., Higgs, J A., Heller, M., Guenther, D., Miller, B., Montzka, S., Miller, J., Conway, T., Dlugokencky, E., Novelli, P., Masarie, K., Oltman, S., and Tans, P.: Carbon dioxide climatology of the NOAA/ESRL Greenhouse Gas Aircraft Network, Journal of Geophysical Research, in prep., 2011. Tans, P P., Fung, I Y., and Takahashi, T.: Observational constraints on the global atmospheric CO<sub>2</sub> budget, Science, 247, 1431–1438, 1990. Tarantola, A.: Inverse Problem Theory and Methods for Model Parameter Estimation, SIAM, (ISBN 0-89871-572-5), 2004. Uliasz, M.: Lagrangian particle modeling in mesoscale applications, in: Environmental Modelling II, edited by: Zanetti, P., Computational Mechanics Publications, 71–102, 1994. Verma, S B., Dobermann, A., Cassman, K G., Walters, D T., Knops, J M., Arkebauer, T J., Suyker, A E., Burba, G G., Amos, B., Yang, H., Ginting, D., Hubbard, K G., Gitelson, A A., and Walter-Shea, E A.: Annual carbon dioxide exchange in irrigated and rainfed maize-based agroecosystems, Agr. Forest Meteorol., 131, 77–96, http://dx.doi.org/10.1016/j.agrformet.2005.05.003doi:10.1016/j.agrformet.2005.05.003, 2005. Wang, J.-W., Denning, A S., Lu, L., Baker, I T., Corbin, K D., and Davis, K J.: Observations and simulations of synoptic, regional, and local variations in atmospheric CO<sub>2</sub>, J. Geophys. Res., 112, D04108, http://dx.doi.org/10.1029/2006JD007410doi:10.1029/2006JD007410, 2007. Wang, W., Davis, K J., Cook, B D., Butler, M P., and Ricciuto, D M.: Decomposing CO<sub>2</sub> fluxes measured over a mixed ecosystem at a tall tower and extending to a region: A case study, J. Geophys. Res., 111, G02005, http://dx.doi.org/10.1029/2005JG000093doi:10.1029/2005JG000093, 2006. West, T O., Bandaru, V., Brandt, C C., Schuh, A E., and Ogle, S M.: Regional uptake and release of crop carbon in the United States, Biogeosciences, 8, 631–654, http://dx.doi.org/10.5194/bg-8-631-2011doi:10.5194/bg-8-631-2011, 2011. Zhao, C L., Tans, P P., and Thoning, K W.: A high precision manometric system for absolute calibrations of CO<sub>2</sub> in dry air, J. Geophys. Res., 102, 5885–5894, 1997.