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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

Atmospheric Tracers and the Great Lakes

Ankur R Desai

University of Wisconsin

questions
Questions
  • Can we “see” Lake Superior in the atmosphere?
    • Lake effect
lake effect
Lake Effect
  • Source: Wikimedia Commons
lake effect4
Lake Effect
  • Source: S.Spak, UW SAGE
questions5
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?
carbon effect
Carbon Effect?
  • Is the NOAA/UW/PSU WLEF tall tower greenhouse gas observatory adequate for sampling Lake Superior air?
first
First
  • A little bit about atmospheric tracers and inversions…
classic inversion
Classic Inversion
  • Source: S. Denning, CSU
regional sources sinks
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
regional sources sinks13
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
where we see
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)
where we see20
Where We See
  • Source: A. Andrews, NOAA ESRL
regional sources sinks21
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
regional sources sinks28
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
terrestrial flux
Terrestrial Flux
  • Annual NEE (gC m-2 yr-1) -160 (-60 – -320)
    • Buffam et al (submitted) -200
problems with regional inversions
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
simpler techniques
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
there is a lake signal
There Is a Lake Signal
  • Source: N. Urban (MTU)
we might see it at wlef
We Might See It at WLEF
  • Source: M. Uliasz, CSU
ebl method helliker et al 2004
EBL method (Helliker et al, 2004)

Mixed layer

Free troposphere

Surface flux

onward
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)
trout lake nee preliminary
Trout Lake NEE (preliminary)
  • Source: M. Balliett, UW
thanks
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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