1. University of California, Berkeley
Using Biophysical Models to Ask (and Answer) Questions About Biosphere-Atmosphere Interactions
Dennis Baldocchi
Alexander Knohl
James Dorsey
Biometeorology Lab
University of California, Berkeley
ILEAP Meeting
Boulder, CO
Jan, 2006

2. ILEAPS Paradigm Isotopic exchange
maybe add isotope fluxes here (see orange)

3. Sub-Grid Variability: What are Errors in ET Scaling?

4. Answering Questions with Models
Diffuse Radiation
Light Use Efficiency
Isoprene emission
Water Use Efficiency
Stable Isotopes
Sub-Grid Parameterization, Energy Balance Closure and Scaling
Insights from a 2-D, ‘Wet’ DaisyWorld

5. CANVeg MODEL Physiology Photosynthesis Stomatal Conductance
Transpiration
Micrometeorology
Leaf/Soil Energy Balance
Radiative Transfer
Lagrangian Turbulent Transfer

6. Key Attributes of CanVeg
Seasonality
Leaf Area Index
Photosynthetic Capacity (Vcmax)
Model parameters based on Site Measurements and EcoPhysiological Rules and Scaling
Stomatal Conductance scales with Photosynthesis
Jmax and Rd scale with Vcmax
Multilayer Framework
Computes Fluxes (non-linear functions) on the basis of a leaf’s local environment
Considers
Sun and Shade Leaf Fraction
Leaf Clumping
Leaf Inclination Angle
Non-local Turbulent Transport and Counter-Gradient Transfer

7. CO2 Flux Model Test: Hourly to Annual Time Scales
Stress need to use ensembles of flux data, not instantaneous data points, they have errors too, both sampling and bias

8. Another Form of Model Testing: Reproducing Spectral Fidelity
Note tested independently by other groups, Simon MPI-Mainz, Knohl MPI Jena, Fuentes Virginia
Baldocchi et al, 2001 Ecological Modeling

9. Results and Discussion

10. How Sky Conditions Affect Net Carbon Exchange (NEE)?: Data
Baldocchi, 1997 PCE

11. CO2 Flux and Diffuse Radiation: Data from AmeriFlux
Niyogi et al., GRL 2004

12. Volcanoes, Aerosols + NEE

13. How do Changes in Diffuse Radiation affect Canopy Fluxes?:
Case: Mt Pinatubo Explosion, ~ 10% of beam -> diffuse
direct beam
Solar radiation [W m-2]
Year of Mt. Pinatubo eruption
legend and labels are very small, I changed it a bit
diffuse
Solar elevation angle [°]
Gu et al, 2003, Science

14. Canopy Photosynthesis and Aerosols: Impact on Daily & Annual Scales, I
increase diffuse by 10% beam: 1527 gC m-2 y-1
+ 51 gC m-2 y-1, the operator += might not be familiar to everybody, maybe better to write “increase diffuse by 10% of beam:” The overall effect is not very large 50 gC = 3%
Canopy Photosynthesis may increase by +50 gC m-2 y-1

15. Conventional Wisdom: More Light Absorption with Diffuse Radiation
WHY?
Conventional Wisdom: More Light Absorption with Diffuse Radiation

16. More Efficient Use of Light by Shade Leaves?
is PPFD only beam? Maybe two figures one with PPFD only beam and one with 0.5 diffuse/total

17. vpd is Correlated with Diffuse Fraction: Less Physiological Stress (?)
Stomatal conductance vs vpd or direct diffuse

18. Isoprene is about >1.1% of canopy photosynthesis on annual basis

19. Isoprene and Diffuse Radiation
0.8% increase, note greatest changes happened on the sunniest and warmest days, indicating a weak but more coupled sensitivity to temperature rather than light

20. Stable Isotope Discrimination and Diffuse Light
Preference of photosynthesis for light 12CO2 vs. heavier 13CO2
I found the equation with deltaa-deltap less clear than a verbal description. Is Delta canopy flux weighted? I guess that high discrimination values mainly occur in the morning and evening hours. Values for delta are very high!

21. Autocorrelations among Ci/Ca, vpd and diffuse/Total

22. Water Use Efficiency (A/T) and diffuse light

23. Simple Model suggests A/T decreases with D or Ci/Ca
e.g. A/T of C4 > C3
But Complex feedbacks need to be considered!

24. How Do Changes in vpd and Ci/Ca conspire to affect A/T?
would it be interesting to look at diffuse/total instead of ci/ca and then in the next slide on A/T vs. ci/ca. I suggest not to use a and b as parameters in the second equations since it looks very much like = a + (b-a) Ci/Ca

25. In toto (considering coupled energy balance feedbacks) A/T increases with Ci/Ca

26. Sub-Grid Variability: Lessons Derived from Wet DaisyWorld
Latent Heat Exchange Map
what is the unit?

27. Eddy covariance footprints and ecosystem representativeness
Footprint representation
Newly developed 3d Lagrangian stochastic footprint model was run for a 1 m canopy and 3 m measurement height. Half a million trajectories were integrated to calculate the source probability density.
The footprint calculation was run using the same grid geometry as the DaisyWorld simulation to allow convolution of the results.
The EC “tower” was placed in different locations in the simulated ecosystem, and the EC system's view of the ecosystem was calculated.

28. Eddy covariance footprints and ecosystem representativeness
Each histogram shows 500 separate tower locations within the simulated ecosystem.

29. Errors in ET Scaling

30. Conclusions
Biophysical Model aids in understanding the impact of diffuse light on photosynthesis, isoprene emission, water use efficiency and stable isotope discrimination
A cellular automata, energy balance model shows that spatial averaging of energy balance drivers can produce huge errors in grid-scale energy fluxes and can explain lack of energy balance closure

31. Acknowledgements Funding Diffuse Light and Carbon Isoprene
NASA, DOE/TCP, NIGEC/WESTGEC
Diffuse Light and Carbon
Lianhong Gu
Isoprene
Peter Harley, Jose Fuentes, Dave Bowling, Russ Monson & Alex Guenther
13C Isotopes
Dave Bowling, Russ Monson
Footprints & DaisyWorld
Monique Leclerc, Tess Krebs, Joon Kim, Peter Levy, HaPe Schmid, Brian Amiro

32. Canopy Photosynthesis and Aerosols:
Impact on Daily & Annual Time Scales, II

33. Role of Diffuse Light on Water Use Efficiency: A/E

34. Baldocchi et al, 2005 Tellus

35. Quantifying Sources and Sinks
Biology:
Leaf area density, a(z)
internal conc, Ci
stomatal resistance, rs
Physics:
Boundary layer resistance, rb
Scalar conc, C(z)

36. Partial Explanation: Fiso is very sensitive to Leaf Temperature, which changed little in response to the imposed direct to diffuse partitioning