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James Orr (LSCE/CEA-CNRS and IPSL, France) Co-authors:

TransCom Workshop Jena, Germany 12—15 May 200 3. Simulations of carbon transport in CCM3: uncertainties in C sinks due to interannual variability and model resolution. James Orr (LSCE/CEA-CNRS and IPSL, France) Co-authors:

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James Orr (LSCE/CEA-CNRS and IPSL, France) Co-authors:

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  1. TransCom Workshop Jena, Germany 12—15 May 2003 Simulations of carbon transport in CCM3: uncertainties in C sinks due to interannual variability and model resolution James Orr (LSCE/CEA-CNRS and IPSL, France) Co-authors: B. Govindasamy & P. Duffy (LLNL/DOE), and J. A. Taylor (ANL/DOE) Funding: LLNL LDRD et LLNL URP sabbatical program

  2. Resolution:~ 50 km CCM3: T239

  3. Resolution:~ 300 km CCM3: T42

  4. Quantitative improvement for T170 *How to measure model improvement? Key relationship: Duffy et al.., Climate Dyn.., submitted, 2003 *Taylor, K. E., J. Geophys. Res., 106, D7, 7183-7192, 2001

  5. TRANSCOM-1 Models *Law et al. (1996, GBC)

  6. Fossil Emissions Scenario (TRANSCOM3) *Gurney et al. (2002, Final TRANSCOM3 Report)

  7. Neutral Biosphere Scenario(TRANSCOM) Transcom3 (2002) Transcom1 (1996) *Gurney et al. (2002, Final TRANSCOM3 Report) *Law et al. (1996, GBC)

  8. * Rectifier correlated withN.H. Land Sink 16 different annual mean model responses to purely seasonal forcing *Gurney et al (2002):Rectifier is the major uncertainty regarding the magnitude of the Northern HemisphereC sink N. H. Land Sink (Pg C yr1) Interhemispheric difference in Rectifier (ppmv)

  9. Objectives of this study • Test sensitivity of rectifier to horizontal resolution • Investigate interannual variability of rectifier in CCM3 model.

  10. Simulations TRANSCOM-3 Boundary Contidtions: • Fossil Emissions: Andres • Ocean : observed air-sea flux (Takahashi et al., 1999) • “Neutral Biosphere” (or Rectifier from CASA model) Other: • Rn-222

  11. Simulation Size Approx Grid Size Years of Simulation Grid Cells T21 64x32 5.6° 600 km 27 T31 96x48 3.8° 450 km 21 T42 128x64 2.8° 300 km 23 T63 192x96 1.9° 225 km 16 T85 256x128 1.4° 150 km 21 T170 512x256 0.7° 75 km In Progress T239 720x360 0.5° 50 km Some model details: • 18 Vertical levels • Climatological SST forcing • Three-year spin-up • Change horizontal resolution only

  12. Taylor Diagram: Precipitation (Effect of Resolution)

  13. Resolution effect: 20-year means

  14. Resolution effect: 20-year means

  15. Rectifier in CCM3 (T42) has large interannual variability *Normalized to South Pole

  16. Variability = f(resolution) T21 T31 T42 T63 T85

  17. Interannual Variability: Zonal Mean (T42)

  18. TRANSCOM-3 Stations

  19. Interannual Variability: TransCom3 Stations (T42)

  20. Spatial distribution of interannual rectifier? Mean Rectifier: T42 (1983-2001) Std. Dev. Range

  21. Causes of interannual variability in the rectifier Mechanisms invoked to explain seasonal rectifier: • Changes in local PBL height (Denning, 1995) • Changes in wind direction (Taguchi, 1996) • Changes in wind speed/”mixing volume” (Taylor, 1998) • Meridional transport • Pearman and Hyson (1980) • Keeling et al. (1989)

  22. Interannual Varib. of PBL Height (m):CCM3 T42 Annual Means (1983—2002)

  23. Winter differences drive interannual variability

  24. R2 for winter monthly anomalies of rectifier vs. surface wind speed(arrows: climatological winter surface winds)

  25. “Neutral Biosphere” : seasonal boundary condition (mol C cm-2 yr-1) *TRANSCOM3 Boundary Condition (also used in this study)

  26. Maximum in Rectifier occurs North of maximum in N.B. forcing

  27. Rectification: Horizontal Control Sink Source Source+Sink Source-Sink *Taguchi (1996, JGR, 101, 15099-15109)

  28. Seasonal Prevailing Surface Winds: CCM3, T42 (1983—2002) NE: Region of Maximum Interannual Rectifier SW: Region of High Corr. (wind, pbl, rectifier)

  29. Interannual variability in MBL pCO2(Globalview Zonal Mean, Detrended 1979-2002)

  30. Interannual variability in MBL pCO2(Globalview Zonal Mean, Detrended 1979-2002)

  31. Conclusions: • Resolution effect: differences but no clear tendency • Systematic bias due to insufficient resolution? • Interannual variability increases with model resolution • Need long high-resolution simulations • Interannual variability of the rectifier: large in CCM3 • Importance of interannual variability of horizontal transport • Comparable to the range of TRANSCOM models • Comparable to observed interannual variability of pCO2 in MBL • Atm. CO2 Growth rate = f(SMS, Interannual Var. in Transport) • Interannual variability in transport likely to differ among models • Inversions with AGCM not appropriate • Effect of Nudging? • Different reanalysis products; different models? • Call for new efforts to constrain effect of interannual variability in atmospheric transport on inverse estimates of C sources and sinks

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