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Modeling Air Movement in the Firn at WAIS-D

Modeling Air Movement in the Firn at WAIS-D. Mark Battle Bowdoin College. WAIS-D meeting NICL July 16, 2006. Possible firn modeling strategies:. Forward model, diffusion only ( Schwander etc. ) Inverse model, diffusion only ( Butler et al.1999)

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Modeling Air Movement in the Firn at WAIS-D

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  1. Modeling Air Movementin the Firn at WAIS-D Mark Battle Bowdoin College WAIS-D meeting NICL July 16, 2006

  2. Possible firn modeling strategies: • Forward model, diffusion only (Schwander etc.) • Inverse model, diffusion only (Butler et al.1999) • Inverse model, diffusion only, a’la Rommelaire • Forward model, diffusion & heat (Severinghaus et al. 2000 ) • Forward model, diffusion & close-off fractionation (Severinghaus & Battle, 2005 ) • Other approaches?

  3. Possible firn modeling strategies: • Forward model, diffusion only(Schwander etc.) • Inverse model, diffusion only (Butler et al.1999) • Inverse model, diffusion only, a’la Rommelaire • Forward model, diffusion & heat (Severinghaus et al. 2000 ) • Forward model, diffusion & close-off fractionation (Severinghaus & Battle, 2005 ) • Other approaches?

  4. Forward model, diffusion onlyWhat are its virtues? • Simple • Good reality check • Can determine age profile vs. depth

  5. Forward model, diffusion onlyOverview Measured density profile

  6. Forward model, diffusion onlyOverview Measured density profile Calculate porosity and diffusivity

  7. Forward model, diffusion onlyOverview Measured density profile Calculate porosity and diffusivity Tune diffusivity until one species’ observations are reproduced

  8. Forward model, diffusion onlyOverview Measured density profile Calculate porosity and diffusivity Tune diffusivity until one species’ observations are reproduced Confirm(?) with other species

  9. Forward model, diffusion onlyOverview Measured density profile Calculate porosity and diffusivity Tune diffusivity until one species’ observations are reproduced Confirm(?) with other species Use it

  10. Field-measured density in various cores at WAIS-D

  11. Fit to density, used for diffusivity starting-point.

  12. How deep is the diffusive column?

  13. How deep is the diffusive column? 64.84mbs

  14. Getting started with CO2

  15. Correcting for Gravitational Fractionation

  16. Getting started with CO2

  17. After Tuning…

  18. After Tuning…

  19. Testing with other species…

  20. Testing with CH4

  21. Testing with CH3CCl3

  22. Testing with F11

  23. Testing with HFC134a

  24. Summary of basic forward model: • No big surprises!!!

  25. Summary of basic forward model: • No big surprises!!! • Density-based diffusivity requires only minor tweaking

  26. Summary of basic forward model: • No big surprises!!! • Density-based diffusivity requires only minor tweaking • XX vs. depth looks generally good for wide range of histories

  27. Summary of basic forward model: • No big surprises!!! • Density-based diffusivity requires only minor tweaking • XX vs. depth looks generally good for wide range of histories • “Gravitational” correction needs more data

  28. Summary of basic forward model: • No big surprises!!! • Density-based diffusivity requires only minor tweaking • XX vs. depth looks generally good for wide range of histories • “Gravitational” correction needs more data • DCH3CCl3/DCO2 consistent with SPO

  29. Summary of basic forward model: • No big surprises!!! • Density-based diffusivity requires only minor tweaking • XX vs. depth looks generally good for wide range of histories • “Gravitational” correction needs more data • DCH3CCl3/DCO2 consistent with SPO • DF11/DCO2 consistent with theory (and not SPO)

  30. Summary of basic forward model: • No big surprises!!! • Density-based diffusivity requires only minor tweaking • XX vs. depth looks generally good for wide range of histories • “Gravitational” correction needs more data • DCH3CCl3/DCO2 consistent with SPO • DF11/DCO2 consistent with theory (and not SPO) • Timing of forcing history crucial (e.g. HFC134a)

  31. Summary of basic forward model: • No big surprises!!! • Density-based diffusivity requires only minor tweaking • XX vs. depth looks generally good for wide range of histories • “Gravitational” correction needs more data • DCH3CCl3/DCO2 consistent with SPO • DF11/DCO2 consistent with theory (and not SPO) • Timing of forcing history crucial (e.g. HFC134a) • Ready to roll…

  32. Where to next? • Characterizing age spread by depth

  33. Where to next? • Characterizing age spread by depth • You tell me…

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