Atmospheric tracers and the great lakes
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Atmospheric Tracers and the Great Lakes. Ankur R Desai University of Wisconsin. Questions. Can we “see” Lake Superior in the atmosphere? Lake effect. Lake Effect. Source: Wikimedia Commons. Lake Effect. Source: S.Spak, UW SAGE. Questions. Can we “see” Lake Superior in the atmosphere?

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Atmospheric tracers and the great lakes l.jpg

Atmospheric Tracers and the Great Lakes

Ankur R Desai

University of Wisconsin


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Questions

  • Can we “see” Lake Superior in the atmosphere?

    • Lake effect


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Lake Effect

  • Source: Wikimedia Commons


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Lake Effect

  • Source: S.Spak, UW SAGE


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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?


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Carbon Effect?

  • Is the NOAA/UW/PSU WLEF tall tower greenhouse gas observatory adequate for sampling Lake Superior air?


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First

  • A little bit about atmospheric tracers and inversions…


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Classic Inversion

  • Source: S. Denning, CSU





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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


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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






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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)



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Where We See

  • Source: A. Andrews, NOAA ESRL


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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




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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




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Terrestrial Flux

  • Annual NEE (gC m-2 yr-1) -160 (-60 – -320)

    • Buffam et al (submitted) -200



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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


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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


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There Is a Lake Signal

  • Source: N. Urban (MTU)


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We Might See It at WLEF

  • Source: M. Uliasz, CSU


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EBL method (Helliker et al, 2004)

Mixed layer

Free troposphere

Surface flux


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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)






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Trout Lake NEE (preliminary)

  • Source: M. Balliett, UW


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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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