regional co 2 fluxes: three approaches
DESCRIPTION
Regional CO 2 Fluxes: Three Approaches. Bakwin et al., Carbon dioxide budget in the continental atmosphere, submitted to Tellus . Helliker et al., Regional-scale measurements of CO 2 flux and stable isotope discrimination across the planetary boundary layer, in preparation. - PowerPoint PPT PresentationTRANSCRIPT
Regional CO2 Fluxes:Three Approaches
1) Bakwin et al., Carbon dioxide budget in the continental atmosphere, submitted to Tellus.
2) Helliker et al., Regional-scale measurements of CO2 flux and stable isotope discrimination across the planetary boundary layer, in preparation.
3) Styles et al., Constraining the terrestrial carbon budget at regional to continental scales with surface concentration measurements, work in progress.
Gloor, M., et al., What is the concentration footprint of a tall tower?J. Geophys. Res., 106, 17831-17840, 2000.
∂CO2/∂t = Fc/Zmix – Ui (∂CO2/∂Xi)
Approach #1: Bakwin et al.Atmospheric budget on a monthly time scale.
Approach #2: Helliker et al.Boundary layer cuvette
Where does this come from?The Lagrangian budget equation is:
but … this is a Lagrangian equation advection has been ignored!
m
i
i
mm
im
c wdtz
zcc
tc
zF
qqcc
FFm
m
qc
• = regional flux estimate, o = tower NEE
You can’t argue with success???
Approach #3: Styles et al.Uncalibrated flux sites
•T is a period of time which starts in the morning before CBL growth begins, and ends in the afternoon when the CBL is fully developed
•cB is CO2 within the CBL
•c+ is CO2 above the CBL
•h = zi (CBL height)
B Bc
c c hF
T
Approach #3: Styles et al.Uncalibrated flux sites
Wait a minute, is this right???
•What about the initial state of the CBL? (h ≠ 0 at t = 0 !)
•This assumes that CO2 above the CBL in the a.m. = c+
Nevertheless, we forge ahead …
B Bc
c c hF
T
You could get (cB – c+) from accurate measurements at a tower (cB) and take c+ as equal to the MBL value.
BUT, flux tower CO2 mixing ratios are usually not well calibrated!
Hence, Styles et al. substitute:
(cmin – cavg) for (cB – c+)
where cmin and cavg are daily minimum and daily average CO2 measured at the flux tower.
Whaaat??? That can’t work!
rain
Time series of daily average CO2 at each height
cB – c+
cmin – cavg
cmin – cavg = 0.915 (cB – c+) – 5.80, r2 = 0.89
cB from 396 m tower data (daily min)c+ from MBL data
cmin and cavg from30 m tower data
SiteLatitude Longitude Elevation Vegetation type
Harvard forest 42.5 -72.2 300 Deciduous
Park Falls 45.8 -90.1 470 Deciduous/coniferous
Willow Creek 45.8 -90.1 520 Deciduous
Boreas NSA 55.9 -98.5 260 Coniferous
Great Mountain 42.0 -73.2 430 Deciduous/coniferous
Univ. MichiganBiol. Station
45.6 -84.7 230 Deciduous/coniferous
Blodgett 38.9 -120.6 1320 Coniferous
Walker Branch 36.0 -84.3 360 Deciduous
Santarem logged -3.0 -55.0 200 Rainforest
WeidenBrunnen 50.2 11.9 780 Coniferous
Hesse 48.7 7.8 300 Deciduous
FLUXNET sites used in Styles et al. analysis
All sites
y = 1.0621x - 4.6905R2 = 0.8158
-30
-25
-20
-15
-10
-5
0
-20 -15 -10 -5 0 5
Fc*daylength/h/rho
avg
dai
ly m
in C
O2
- av
g C
O2
Conclusions
• Three very different approaches, each with very dubious simplifying assumptions, all give some reasonable-looking results.
• Are we just lucky? Stupid? Both?