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? 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/Sinks

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 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

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

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

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

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