Merging CO 2 flux and mixing ratio observations at daily, synoptic, seasonal and interannual scales Funded in part by the ChEAS Research Collaboration Network, NSF ChEAS flux measurements supported by NIGEC Midwestern Regional Center ChEAS mixing ratio measurements supported by NIGEC and NOAA/CMDL

Agenda 2:20-30Davis, intro Recent progress/papers 2:30-40Bakwin, monthly mean ABL co2 budgets 2:40-50Helliker, synoptic flux-gradient approach 2:50-3Styles, daily ABL co2 budgets 3-3:10Davis, fronts and synthesis Break, discussion Recent observations/ongoing work 3:30-40Shashkov, airborne profiles 3:40-50Fischer, SGP ARM-CART site 3:50-4Davis, IHOP, ChEAS Break, discussion Modeling/network design 4:20-30Denning/Uliasz, ChEAS modeling, network design studies 4:30-40Schimel, Network design workshop results Future experiments, analyses, instruments, papers, proposals 4:40-50Davis, ChEAS, COBRA-Maine, NACP 2005 Discussion Thursday morning, NCAR Foothills Lab, FL1 Room am start. Done by noon or so.

Why meet now? NACP is coming! (?) Several efforts at interpreting CO 2 mixing ratios to infer regional fluxes have emerged very recently. Disseminate this information and discuss. Pre-NACP regional field projects will happen in the next 2 years. Some have already occurred. AmeriFlux towers need to measure [CO 2 ] in support of NACP. Instrumentation is needed. Drainage flows continue to be a problem. Addressing this is more difficult than many hoped, and requires improved instrumentation.

Goals Obtain a mechanistic understanding of tower to regional-scale variability in NEE of CO 2. + Link observed regional fluxes with the global CO 2 flask network. = Understand the mechanisms that govern interannual changes in the atmospheric CO 2 budget. Tools for this discussion: Merge flux tower and CO 2 mixing ratio data.

Atmospheric approaches to observing the terrestrial carbon cycle Time rate of change (e.g. CO 2 ) Mean transport Turbulent transport (flux) Source in the atmosphere Average over the depth of the atmosphere (or the ABL): F 0 C encompasses all surface exchange: Oceans, deforestation, terrestrial uptake, fossil fuel emissions. Inversion study: Observe C, model U, derive F Flux study: Observe F directly

Methods for determining NEE of CO 2 Methods for bridging the gap Upscale via ecosystem models and networks of towers. Move towards regional inverse modeling

Goals of this gathering Discuss recent results. Synthesize and summarize our understanding. Plan future analyses and publications. Plan future field experiments and proposals.

Current work - overview Papers by: –Bakwin, Davis: Monthly-scale ABL CO 2 budgets (Davis et al, in press, GCB; Bakwin et al, submitted, Tellus) –Helliker: Monthly-scale flux-gradient. (Helliker et al, submitted to PNAS) –Styles: Daily ABL CO 2 budgets (Styles et al, paper in prep) –Hurwitz: Synoptic case studies (Hurwitz et al, submitted to JAS) –Davis, Bakwin: Document difference between surface and mid-ABL mixing ratio measurements. (Bakwin et al, 1998, Tellus; Davis et al, in prep forever) –Gerbig, Lin: Aircraft-based Lagrangian CO 2 budgets (Two papers in preparation) –Denning: Regional modeling of fluxes and atmospheric [CO 2 ] (Denning et al, in press, GCB) –Gloor, Uliasz: Footprints of ABL CO 2, network design (Gloor et al, 1999, JGR; Uliasz et al, in preparation) –Wang: Local advection in ChEAS using two towers. (Wang et al, in prep) –Hurwitz, Jensen: ABL budgets using powered parachute (Hurwitz et al, in prep)

Agenda 2:20-30Davis, intro Recent progress/papers 2:30-40Bakwin, monthly mean ABL co2 budgets 2:40-50Helliker, synoptic flux-gradient approach 2:50-3Styles, daily ABL co2 budgets 3-3:10Davis, fronts and synthesis Break, discussion Recent observations/ongoing work 3:30-40Shashkov, airborne profiles 3:40-50Fischer, SGP ARM-CART site 3:50-4Davis, IHOP, ChEAS Break, discussion Modeling/network design 4:20-30Denning/Uliasz, ChEAS modeling, network design studies 4:30-40Schimel, Network design workshop results Future experiments, analyses, instruments, papers, proposals 4:40-50Davis, ChEAS, COBRA-Maine, NACP 2005 Discussion

Frontal passage: WLEF tower Park Falls, Wisc. 14 July, 1998 Large, sustained downdraft, change in wind direction. CO 2 mixing ratio jumps > 20 ppm in ~90 seconds. Extreme magnitude but common pattern.

synthesis See cartoon –Seasonal, syntopic and diurnal patterns, and Helliker, Bakwin, Styles and Davis results in this context. –Theoretical basis for the Styles and Helliker results Major conclusions –[co2] data is fairly easy to relate to regional, seasonal fluxes, and perhaps annual net fluxes –Similarity with other scalars (e.g. H 2 O, maybe radon) may greatly improve our ability to interpret [co2] data –Additional [co2] measurements (~20 sites in N. America?) are called for! –Additional analyses/tests of simple interpretation methods is also called for!

Agenda 2:20-30Davis, intro Recent progress/papers 2:30-40Bakwin, monthly mean ABL co2 budgets 2:40-50Helliker, synoptic flux-gradient approach 2:50-3Styles, daily ABL co2 budgets 3-3:10Davis, fronts and synthesis Break, discussion Recent observations/ongoing work 3:30-40Shashkov, airborne profiles 3:40-50Fischer, SGP ARM-CART site 3:50-4Davis, IHOP, ChEAS Break, discussion Modeling/network design 4:20-30Denning/Uliasz, ChEAS modeling, network design studies 4:30-40Schimel, Network design workshop results Future experiments, analyses, instruments, papers, proposals 4:40-50Davis, ChEAS, COBRA-Maine, NACP 2005 Discussion

[CO 2 ] observational efforts Current flux towers –All sites measure daily CO 2 fluctuations well (?) Current calibrated towers –6-10 have well-calibrated (accurate and precise) CO 2. –ChEAS (4 sites), Harvard, NOBS, ARM-CART, Howland, Hungary, 2 LBA sites Regional [co2] experiments – already done –IHOP, Spring Aircraft (flux and CO 2 ). 4 towers. –(Jensen and Birks airborne profiling experiment) –ChEAS, continuous. 4 towers. Continental measurements funded –About 10 tall towers, 10 airborne profiling sites Regional experiments – planned –NIGEC-funded airborne eddy flux project, Nebraska. Oechel and Running. Details unknown. –ChEAS, intensive campaign. Planned for 2003, maybe –COBRA-Maine –NACP – Iowa, 2005?

ChEAS sites and neighbors: 4 currently well-calibrated, UMBS planned. Continuous regional budget analyses planned using 4-site mesonet + NOAA aircraft

IHOP, Spring 2002 Oklahoma-Kansas, May-June, towers with well-calibrated CO 2 –ARM-CART CF, Texas tall tower, 2 NCAR ISFF portable flux towers –Spacing of roughly 200km between towers Cessna-borne flask samples for about 10 days, U. Colorado, M.Jensen and J. Birks. –Vertical profiles near ARM-CART site –100km transects extending to the west in the mid-CBL University of Wyoming King Air airborne eddy covariance fluxes and [co2] measurements. –3 60km long tracks, 2 in southern KS and 1 in the OK panhandle. Ability to resolve surface fluxes (65m AGL flights) down to a spatial resolution of 2km or better. –Vertical soundings –[co2] calibration unproven Fischer et al mobile flux towers deployed in addition to ARM-CART CF. –3? continuous flux towers. –Also 9 NCAR flux towers, but lacking CO2 flux. Airborne Differential Absorption Lidar (DIAL) H 2 O “curtains” –200 to 300 km swaths –data from ground to 3-4km altitude –3 different aircraft/DIAL systems.

Agenda 2:20-30Davis, intro Recent progress/papers 2:30-40Bakwin, monthly mean ABL co2 budgets 2:40-50Helliker, synoptic flux-gradient approach 2:50-3Styles, daily ABL co2 budgets 3-3:10Davis, fronts and synthesis Break, discussion Recent observations/ongoing work 3:30-40Shashkov, airborne profiles 3:40-50Fischer, SGP ARM-CART site 3:50-4Davis, IHOP, ChEAS Break, discussion Modeling/network design 4:20-30Denning/Uliasz, ChEAS modeling, network design studies 4:30-40Schimel, Network design workshop results Future experiments, analyses, instruments, papers, proposals 4:40-50Davis, ChEAS, COBRA-Maine, NACP 2005 Discussion

[CO 2 ] observational efforts Current flux towers –All sites measure daily CO 2 fluctuations well (?) Current calibrated towers –6-10 have well-calibrated (accurate and precise) CO 2. –ChEAS (4 sites), Harvard, NOBS, ARM-CART, Howland, Hungary, 2 LBA sites Regional [co2] experiments – already done –IHOP, Spring Aircraft (flux and CO 2 ). 4 towers. –(Jensen and Birks airborne profiling experiment) –ChEAS, continuous. 4 towers. Continental measurements funded –About 10 tall towers, 10 airborne profiling sites Regional experiments – planned –NIGEC-funded airborne eddy flux project, Nebraska. Oechel and Running. Details unknown. –ChEAS, intensive campaign. Planned for 2003, maybe –COBRA-Maine –NACP – Iowa, 2005?

Regional Ecosystem-Atmosphere Exchange of CO 2 via Atmospheric Budgets DoE/TCP funded project, Davis, Richardson and Denning, 2003 and 2004 field deployments anticipated Roughly 6 well-calibrated CO 2 instruments funded (in search of flux towers or other platforms) to build a regional mesonet at two spatial scales, ~100km and ~400km. One CO sensor and funds for an airborne CO 2 sensor also available, depending on tower platform costs/availability. Use budget equation, including horizontal advection, to estimate regional surface fluxes. Comparison to flux towers, airborne eddy covariance fluxes, ecosystem models (SiB2, ED), airborne [CO 2 ] regional transects or vertical profiles desired. Experiment with regional inverse modeling.

Detectability of regional ABL CO 2 gradients Separation between sensors 100km400km Advection time between sensors ~1/4 day~1 day  CO 2 | for F(daytime) 6 ppmnot appropriate  CO 2 | for F(daily mean) not appropriate10 ppm | CO 2 (mid-CBL) – CO 2 (surface layer) | ~ 2 ppm midday, summer fluxes

Figure 3: Possible sampling locations for regional flux estimation Possible ChEAS deployment plan for Major uncertainty at the moment is access to suitable tower platforms (flux or nonflux) Additional uncertainty is the construction of the instruments. Should we pursue a larger number of less expensive sensors? Many cheaper sensors could also be used nationally (virtual tall towers) or for microscale advection studies.

COBRA - Maine 2004 field campaigns. NSF supported, so ATD requests are possible (e.g. flux aircraft, flux towers). Currently lacking a CO 2 network. Complementary efforts.

Other possible projects NACP regional intensive, Somewhat larger scale than ChEAS, COBRA-Maine, in order to address the annual net flux of CO 2. Microscale drainage study. Continental scale, flux-tower-based (+ other towers?) [CO 2 ] network. (Virtual tall towers idea).

Instruments Flasks (Globalview network) Uncalibrated IRGAs (most tower sites) Bakwin calibration of IRGAs (mainly LI- COR). Existing well-calibrated sites. NOAA high-precision, high-accuracy sensor. Under development. Calibration of less expensive IRGAs. Also under development. (Remote sensing – FTIR, lidar)

Discussion Future experiments –Additions to ChEAS/Maine ideas? –Additional ideas beyond ChEAS/Maine? –Continental [co2] network –Microscale drainage experiment Additional analyses/papers that are needed –Helliker et al for more years at WLEF –Helliker et al for more sites across N. America –Full CO 2 and H 2 O budgets. Sites? –Analysis of IHOP 2002 data. Instrument development –Stephens, Richardson, Baldocchi, Euroflux – all experimenting with cheap CO 2 sensors –New proposal to a) fund AmeriFlux [CO 2 ] with existing technology and b) develop technology for cheap and abundant CO 2 sensors Funding for new work –NSF MRI? Biocomplexity? Other ideas?