1. A direct carbon budgeting approach to study CO 2 sources and sinks ICDC7 Broomfield, 25-30 September 2005 C. Crevoisier 1 E. Gloor 1, J. Sarmiento 1, L. Horowitz 2, S. Malyshev 2, E. Shevliakova 2, C. Sweeney 3, A. Andrews 3, P. Tans 3

2. Aircraft measurements: Determining the location, the intensity and the evolution in time of the sink of carbon in the northern hemisphere remains one of the main issues in carbon cycle study. Huge amount of measurements of CO 2 by aircraft and tall towers will soon be available at many locations across the United States, in the framework of the North American Carbon Plan. This should allow the design of new estimation methods, possibly avoiding the use of a priori information. Direct carbon budgeting approach and test of the network. Introduction Measurements up to 8 km once per week. 19 sites + 3 new sites (2006).

3. Let’s put a ‘box’ over the region where we want to estimate surface fluxes. Direct carbon budgeting approach surface CO 2 fluxes In Out Exchanges with the upper atmosphere (convection, advection) h dC/dt = (F h in -F h out ) - F vertical + F surf Observations aircrafts + towers. Following the existing network, we chose: h =8km. box over the US + South Canada. ? Carbon mass budget

4. Simulations of atmospheric CO 2 dC/dt F surf 2 0 -4 -2 MOZART atmospheric transport/chemistry model NCEP (2 º  2 º, 29 levels) CO 2 air/land fluxesmonthly fossil fuel emissionsair/sea fluxes CASA model GFDL, J. Dunne[Blasing et al. 2004] dC/dt = (F h in -F h out ) - F vertical + F surf From these simulations, we can compute each term of the carbon mass budget. (GtC.month -1 ) what we want to retrieve… [Horowitz et al. 2003] [Randerson et al. 1997] month

5. Horizontal Fluxes: Advection dC/dt = (F h in -F h out ) - F vertical + F surf e.g.: November + - + - Evolution of the horizontal fluxes along the edges of the box: income and outcome pathways. InOut In Out Center: NCEP winds

6. Horizontal Fluxes: Advection dC/dt = (F h in -F h out ) - F vertical + F surf e.g.: November - + - Evolution of the horizontal fluxes along the edges of the box: income and outcome pathways. Out In Center: NCEP winds Monthly variation (sum along the edges) F h in -F h out dC/dt F surf 2 0 -4 -2 (GtC.month -1 ) month

7. Vertical fluxes: convection (and advection) at h=8 km Convection fluxes summer - h=8km dC/dt = (F h in -F h out ) - F vertical + F surf F h in -F h out dC/dt F surf Monthly variation convection vertical advection 2 0 -4 -2 month (kgC.m -2.s -1 )

8. At h=8 km, the vertical fluxes are small but the lower the altitude, the higher the convection flux. Vertical fluxes: convection (and advection) at h=8 km 8 km 5 km 700m Convection fluxes summer - h=8km Monthly convection flux at different levels dC/dt = (F h in -F h out ) - F vertical + F surf F h in -F h out dC/dt F surf Monthly variation convection vertical advection 2 0 -4 -2 0 -0.2 -0.6 -0.4 (GtC.month -1 ) month (kgC.m -2.s -1 )

9. Study of the Observation Network From CO 2 simulated at 19 sites, we infer CO 2 in the whole US. Use of a geostatistical interpolation technique: kriging.

10. Study of the Observation Network From CO 2 simulated at 19 sites, we infer CO 2 in the whole US. Use of a geostatistical interpolation technique: kriging. Monthly mean error on CO 2 mixing ration (integrated content 0-8 km) (ppmv)

11. Error on CO 2 mixing ratio after interpolation Winds Surface fluxes Example: Error in July The corresponding error on flux estimation is 19.3 %. 1 0 1.5 0 -1.5 (ppmv) (kgC.m -2.yr -1 )

12. The error on flux estimation is reduced to 8.3 %. Network design A way to reduce the interpolation error: adding a few stations… e.g.: one more station in NW [55N;110W] 1 0 1 0 Monthly error on CO 2 mixing ratio - August Planned network+ 1 station (ppmv)

13. Extending the method to higher spatial (0.5°) and temporal (hourly) resolutions. Conclusions and perspectives The main target is the convection. Some ways to estimate it: With a few more stations in NW and SW, we should be able to have an accurate description of CO 2 in the US. Estimated surface fluxes = biospheric fluxes + fossil fuel emissions. Using other tracers (O 3, APO~O 2 +1.1xCO 2, SF 6, others?). CO 2 from satellite (measurements in the mid to high troposphere) to fix the top of the box. A direct budgeting approach seems possible with the high density measurements … at least on simulations! use of other tracers to separate both contribution ( 14 CO 2 ). Applying the method in restricted regions where no convection. Estimation of the errors (interpolation, convection, etc).