1. Atmospheric Tracers and the Great Lakes
Ankur R Desai
University of Wisconsin

2. Questions
Can we “see” Lake Superior in the atmosphere?
Lake effect

3. Lake Effect
Source: Wikimedia Commons

4. Lake Effect
Source: S.Spak, UW SAGE

5. Questions Can we “see” Lake Superior in the atmosphere?
Lake effect
Carbon effect?
If so, can we constrain air-lake exchange by atmospheric observations?
If that, can we compare terrestrial and aquatic regional fluxes?

6. Carbon Effect?
Is the NOAA/UW/PSU WLEF tall tower greenhouse gas observatory adequate for sampling Lake Superior air?

7. First
A little bit about atmospheric tracers and inversions…

8. Classic Inversion
Source: S. Denning, CSU

9. Source: NOAA ESRL

10. Flask Analysis

11. Gurney et al (2002) Nature

12. Regional Sources/Sinks
Global cooperative sampling network not sufficient to detail processes at sub-seasonal, sub-continental, and sub-biome scale
Weekly/monthly sampling
Low spatial density
Poorly constrained inversion

13. Regional Sources/Sinks
Global cooperative sampling network not sufficient to detail processes at sub-seasonal, sub-continental, and sub-biome scale
Weekly/monthly sampling
Low spatial density
Poorly constrained inversion

14. A Tall Tower

15. In Situ Sampling

16. What We See

17. Continental Sources/Sinks

18. Where We See
Surface footprint influence function for tracer concentrations can be computed with LaGrangian ensemble back trajectories
transport model wind fields, mixing depths (WRF)
particle model (STILT)

19. Where We See

20. Where We See
Source: A. Andrews, NOAA ESRL

21. Regional Sources/Sinks
Global cooperative sampling network not sufficient to detail processes at sub-seasonal, sub-continental, and sub-biome scale
Weekly/monthly sampling
Low spatial density
Poorly constrained inversion

26. NOAA Tall Tower Network

27. Tower Sensitivities

28. Regional Sources/Sinks
Global cooperative sampling network not sufficient to detail processes at sub-seasonal, sub-continental, and sub-biome scale
Weekly/monthly sampling
Low spatial density
Poorly constrained inversion

29. Bayesian Regional Inversions

30. CarbonTracker (NOAA)

31. Terrestrial Flux Annual NEE (gC m-2 yr-1) -160 (-60 – -320)
Buffam et al (submitted) -200

32. CarbonTracker (NOAA)

33. Problems With Regional Inversions
It is still an under-constrained problem!
Assumptions about surface forcing can skew results
Great Lakes are usually ignored
Sensitive to assumptions about “inflow” fluxes
Sensitive to error covariance structure in Bayesian optimization
Transport models have more error at higher resolution
Great Lakes have complex meteorology

34. Simpler Techniques Boundary Layer Budgeting Equilibrium Boundary Layer
Compare [CO2] of lake and non-lake trajectory air
WRF-STILT nested grid tracer transport model
Estimate boundary layer depth and advection timescale to yield flux
Equilibrium Boundary Layer
Compare [CO2] of free troposphere and boundary layer air averaged over synoptic cycles
Estimate subsidence rate to yield flux

35. There Is a Lake Signal
Source: N. Urban (MTU)

36. We Might See It at WLEF
Source: M. Uliasz, CSU

37. EBL method (Helliker et al, 2004)
Mixed layer
Free troposphere
Surface flux

38. Onward
Trajectory analysis and simple budgets – see next talk by Victoria Vasys
Attempting regional flux inversions with lakes explicitly considered – in progress (A. Schuh, CSU)
Direct eddy flux measurements over the lake – in progress (P. Blanken, CU; N. Urban, MTU)

39. I See Eddies

40. Fluxnet

41. Flux Mesonet

42. Lost Creek Shrub “Wetland”

43. Trout Lake NEE (preliminary)
Source: M. Balliett, UW

44. Thanks!
CyCLeS project: G. Mckinley, N. Urban, C. Wu, V. Bennington, N. Atilla, C. Mouw, and others, NSF
NSF REU: Victoria Vasys
WLEF: A. Andrews, NOAA ESRL, R. Strand, WI ECB; J. Thom, UW; R. Teclaw, D. Baumann, USFS NRS
WRF-STILT: A. Michalak, D. Huntzinger, S. Gourdji, U. Michigan; J. Eluszkiewicz, AER
Regional Inversions: M. Uliasz, S. Denning, A. Schuh, CSU
EBL: B. Helliker, U. Penn
Eddy flux: P. Blanken, CU