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Regional CO 2 Fluxes: Three Approaches

Regional CO 2 Fluxes: Three Approaches. Bakwin et al., Carbon dioxide budget in the continental atmosphere, submitted to Tellus . Helliker et al., Regional-scale measurements of CO 2 flux and stable isotope discrimination across the planetary boundary layer, in preparation.

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Regional CO 2 Fluxes: Three Approaches

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  1. Regional CO2 Fluxes:Three Approaches • Bakwin et al., Carbon dioxide budget in the continental atmosphere, submitted to Tellus. • Helliker et al., Regional-scale measurements of CO2 flux and stable isotope discrimination across the planetary boundary layer, in preparation. • Styles et al., Constraining the terrestrial carbon budget at regional to continental scales with surface concentration measurements, work in progress.

  2. Gloor, M., et al., What is the concentration footprint of a tall tower? J. Geophys. Res., 106, 17831-17840, 2000.

  3. Approach #1: Bakwin et al. Atmospheric budget on a monthly time scale. ∂CO2/∂t = Fc/Zmix – Ui (∂CO2/∂Xi)

  4. Approach #2: Helliker et al.Boundary layer cuvette Where does this come from? The Lagrangian budget equation is: but … this is a Lagrangian equation  advection has been ignored!

  5. •= regional flux estimate, o = tower NEE

  6. You can’t argue with success???

  7. Approach #3: Styles et al.Uncalibrated flux sites • T is a period of time which starts in the morning before CBL growth begins, and ends in the afternoon when the CBL is fully developed • cB is CO2 within the CBL • c+ is CO2 above the CBL • h = zi (CBL height)

  8. Approach #3: Styles et al.Uncalibrated flux sites • Wait a minute, is this right??? • What about the initial state of the CBL? (h ≠ 0 at t = 0 !) • This assumes that CO2 above the CBL in the a.m. = c+ • Nevertheless, we forge ahead …

  9. You could get (cB – c+) from accurate measurements at a tower (cB) and take c+ as equal to the MBL value. BUT, flux tower CO2 mixing ratios are usually not well calibrated! Hence, Styles et al. substitute: (cmin – cavg) for (cB – c+) where cmin and cavg are daily minimum and daily average CO2 measured at the flux tower. Whaaat??? That can’t work!

  10. rain

  11. Time series of daily average CO2 at each height

  12. cmin – cavg = 0.915 (cB – c+) – 5.80, r2 = 0.89 cB – c+ cmin –cavg

  13. cmin and cavg from 30 m tower data cB from 396 m tower data (daily min) c+ from MBL data

  14. FLUXNET sites used in Styles et al. analysis

  15. Conclusions • Three very different approaches, each with very dubious simplifying assumptions, all give some reasonable-looking results. • Are we just lucky? Stupid? Both?

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