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Using Biophysical Models to Ask (and Answer) Questions About Biosphere-Atmosphere Interactions

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. ILEAPS Paradigm. Isotopic exchange.

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Using Biophysical Models to Ask (and Answer) Questions About Biosphere-Atmosphere Interactions

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  1. 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 Isotopicexchange

  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

  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

  8. Another Form of Model Testing: Reproducing Spectral Fidelity 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. Pinatuboeruption 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 Canopy Photosynthesis may increase by +50 gC m-2 y-1

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

  16. More Efficient Use of Light by Shade Leaves?

  17. vpd is Correlated with Diffuse Fraction: Less Physiological Stress (?)

  18. Isoprene and Diffuse Radiation

  19. Stable Isotope Discrimination and Diffuse Light Preference of photosynthesis for light 12CO2 vs. heavier 13CO2

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

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

  22. 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!

  23. How Do Changes in vpd and Ci/Ca conspire to affect A/T?

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

  25. Sub-Grid Variability: Lessons Derived from Wet DaisyWorld Latent Heat Exchange Map

  26. 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.

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

  28. Errors in ET Scaling

  29. 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

  30. Acknowledgements • Funding • 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

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

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

  33. Baldocchi et al, 2005 Tellus

  34. 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)

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

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