Using Biophysical Models to Ask and Answer Questions
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
Sub-Grid Variability: What are Errors in ET Scaling?
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’ Daisy. World
CANVeg MODEL Physiology Photosynthesis Stomatal Conductance Transpiration Micrometeorology Leaf/Soil Energy Balance Radiative Transfer Lagrangian Turbulent Transfer
Key Attributes of Can. Veg • • • Seasonality – Leaf Area Index – Photosynthetic Capacity (Vcmax) Model parameters based on Site Measurements and Eco. Physiological 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
CO 2 Flux Model Test: Hourly to Annual Time Scales
Another Form of Model Testing: Reproducing Spectral Fidelity Baldocchi et al, 2001 Ecological Modeling
Results and Discussion
How Sky Conditions Affect Net Carbon Exchange (NEE)? : Data Baldocchi, 1997 PCE
CO 2 Flux and Diffuse Radiation: Data from Ameri. Flux Niyogi et al. , GRL 2004
Volcanoes, Aerosols + NEE
direct beam Year of Mt. Pinatubo eruption diffuse Solar radiation [W m-2] How do Changes in Diffuse Radiation affect Canopy Fluxes? : Case: Mt Pinatubo Explosion, ~ 10% of beam -> diffuse Solar elevation angle [°] Gu et al, 2003, Science
Canopy Photosynthesis and Aerosols: Impact on Daily & Annual Scales, I increase diffuse by 10% beam: 1527 g. C m-2 y-1 Canopy Photosynthesis may increase by +50 g. C m-2 y-1
WHY? Conventional Wisdom: More Light Absorption with Diffuse Radiation
More Efficient Use of Light by Shade Leaves?
vpd is Correlated with Diffuse Fraction: Less Physiological Stress (? )
Isoprene and Diffuse Radiation
Stable Isotope Discrimination and Diffuse Light Preference of photosynthesis for light 12 CO 2 vs. heavier 13 CO 2
Autocorrelations among Ci/Ca, vpd and diffuse/Total
Water Use Efficiency (A/T) and diffuse light
Simple Model suggests A/T decreases with D or Ci/Ca e. g. A/T of C 4 > C 3 But Complex feedbacks need to be considered!
How Do Changes in vpd and Ci/Ca conspire to affect A/T?
In toto (considering coupled energy balance feedbacks) A/T increases with Ci/Ca
Sub-Grid Variability: Lessons Derived from Wet Daisy. World Latent Heat Exchange Map
Eddy covariance footprints and ecosystem representativeness Footprint representation Newly developed 3 d 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 Daisy. World 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.
Eddy covariance footprints and ecosystem representativeness Each histogram shows 500 separate tower locations within the simulated ecosystem.
Errors in ET Scaling
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
Acknowledgements • Funding – NASA, DOE/TCP, NIGEC/WESTGEC • Diffuse Light and Carbon – Lianhong Gu • Isoprene – Peter Harley, Jose Fuentes, Dave Bowling, Russ Monson & Alex Guenther • 13 C Isotopes – Dave Bowling, Russ Monson • Footprints & Daisy. World – Monique Leclerc, Tess Krebs, Joon Kim, Peter Levy, Ha. Pe Schmid, Brian Amiro
Canopy Photosynthesis and Aerosols: Impact on Daily & Annual Time Scales, II
Role of Diffuse Light on Water Use Efficiency: A/E
Baldocchi et al, 2005 Tellus
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)
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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