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Atmospheric Tracers and Lake Superior: Exploring Air-Lake Exchange Dynamics

This study investigates the visibility of Lake Superior in atmospheric data through the lens of atmospheric tracers. It addresses the lake effect and carbon exchange between air and water, posing critical questions about the adequacy of existing observational networks to sample the lake's atmospheric influence. By examining regional sources and sinks, utilizing tall tower measurements, and considering Bayesian regional inversions, the research aims to enhance our understanding of the complex interactions between terrestrial and aquatic carbon fluxes, especially in the context of the Great Lakes' unique meteorology.

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Atmospheric Tracers and Lake Superior: Exploring Air-Lake Exchange Dynamics

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  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

  22. NOAA Tall Tower Network

  23. Tower Sensitivities

  24. 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

  25. Bayesian Regional Inversions

  26. CarbonTracker (NOAA)

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

  28. CarbonTracker (NOAA)

  29. 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

  30. Simpler Techniques • Boundary Layer Budgeting • 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

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

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

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

  34. 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)

  35. I See Eddies

  36. Fluxnet

  37. Flux Mesonet

  38. Lost Creek Shrub “Wetland”

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

  40. 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

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