1. Modeling Air Movement in 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 only What are its virtues? Simple Good reality check Can determine age profile vs. depth

5. Forward model, diffusion only Overview Measured density profile

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

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

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

9. Forward model, diffusion only Overview 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. 64.84mbs

14. Getting started with CO 2

15. Correcting for Gravitational Fractionation

16. Getting started with CO 2

17. After Tuning…

19. Testing with other species…

20. Testing with CH 4

21. Testing with CH 3 CCl 3

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 D CH 3 CCl 3 /D CO 2 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 D CH 3 CCl 3 /D CO 2 consistent with SPO D F11 /D CO 2 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 D CH 3 CCl 3 /D CO 2 consistent with SPO D F11 /D CO 2 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 D CH 3 CCl 3 /D CO 2 consistent with SPO D F11 /D CO 2 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…