Atmospheric Tracers and the Great Lakes

Ankur R DesaiUniversity 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?– 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?

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

First

• A little bit about atmospheric tracers and inversions…

Classic Inversion

• Source: S. Denning, CSU

• Source: NOAA ESRL

Flask Analysis

Gurney et al (2002) Nature

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/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

A Tall Tower

In Situ Sampling

What We See

Continental Sources/SinksWLEF Park Falls, WI 396m

330

340

350

360

370

380

390

400

1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006

Year

CO

2 (p

pm

)

Daily 10am-2pm Tower (NOAA Globalview) Marine Background

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 See

Where We See

• Source: A. Andrews, NOAA ESRL

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

NOAA Tall Tower Network

Tower Sensitivities

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

Bayesian Regional Inversions

CarbonTracker (NOAA)

Terrestrial Flux

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

CarbonTracker (NOAA)

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

• 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

• Source: N. Urban (MTU)

We Might See It at WLEF

• Source: M. Uliasz, CSU

5 6 7 8 9 10 11m onths

-8

-6

-4

-2

0

2

4

6

!CO2 [ppm]

5 6 7 8 9 10 11m onths

-8

-6

-4

-2

0

2

4

6

!CO2 [ppm]

EBL method (Helliker et al, 2004)

Mixed layer

Surface flux

Free troposphere

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)

I See Eddies

Fluxnet

Flux Mesonet

Lost Creek Shrub “Wetland”

Trout Lake NEE (preliminary)

• Source: M. Balliett, UW

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