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Ian Baker ChEAS Annual Meeting Kemp Research Station 01 June 2005

Radiation Schemes in Biophysical Models: Big Leaf vs. 2-Leaf Submodel in the Simple Biosphere Model (SiB). Ian Baker ChEAS Annual Meeting Kemp Research Station 01 June 2005. MOTIVATION. SiB2/SiB3 Comparison Latent heat flux for both versions looks good NEE looks better in SiB3

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Ian Baker ChEAS Annual Meeting Kemp Research Station 01 June 2005

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  1. Radiation Schemes in Biophysical Models: Big Leaf vs. 2-Leaf Submodel in the Simple Biosphere Model (SiB) Ian Baker ChEAS Annual Meeting Kemp Research Station 01 June 2005

  2. MOTIVATION • SiB2/SiB3 Comparison • Latent heat flux for both versions looks good • NEE looks better in SiB3 • H is worse in SiB3! • new water stress • Is radiative scheme the problem? • Wetlands?

  3. SiB: Big Leaf Radiation

  4. SiB: Big Leaf Radiation • Linkage: Photosynthesis and leaf energetics coupled through stomatal resistance • Inconsistent: Diffuse light neglected in photosynthesis is accounted for in leaf energetics • MY PET THEORY: In wet, dense canopy environments, potential for leaf heating with insufficient transpiration (i.e. photosynthesis) to cool leaf

  5. 2-Leaf Radiation

  6. Does it work? • Sure looks like it • H much lower in summer months • LE increases • Must make adjustments to keep photosynthesis and respiration reasonable

  7. Bowen Ratio • 2-leaf Bowen Ratio lower than Big-leaf BR in summer • Both models have trouble in spring, 2L worse

  8. Adjustments to Photosynthesis • Two ‘knobs’ • Vm calculation (sun and shade leaves) • de Pury & Farquhar • Wang & Leuning • Vmax value • From tables • Adjusted (Collatz)

  9. Ongoing Issues • Conservation of energy and water: small amounts of imbalance exist. Re-deriving equations will remedy this • Parameters (not just VMAX0) have been developed for big-leaf model-are they incorrect for two-leaf model? • Two-leaf SiB looks good at WLEF; How about other sites (grassland, tropics)?

  10. Some References • Dai, Y., R.E. Dickinson, Y.-P. Wang, 1998: A Two-Leaf Model for Canopy Temperature, Photosynthesis, and Stomatal Conductance. Journal of Climate, 17, 2281-2299. • De Pury, D.G.G., Farquhar, G.D, 1997: Simple Scaling of Photosynthesis from Leaves to Canopies without the errors of Big-Leaf Models. Plant, Cell, and Environment, 20, 537-557. • Dickinson, R.E., 1983: Land Surface Processes and Climate-Surface Albedos and Energy Balance. Advances in Geophysics, 25,305. • Sellers, P.J., 1985: Canopy Reflectance, Photosynthesis and Transpiration. International Journal of Remote Sensing, 6(8), 1335-1372. • Sellers, P.J., J.A. Berry, G.J. Collatz, C.B. Field, F.G. Hall, 1992: Canopy Reflectance, Photosynthesis, and Transpiration. III. A Reanalysis Using Improved Leaf Models and a New Canopy Integration Scheme. Remote Sensing and Environment, 42: 187-216. • Wang, Y.-P., Leuning, R., 1998: A Two-Leaf Model for Canopy Conductance, Photosynthesis and Partitioning of Available Energy I: Model Description and Comparison with a Multi-Layered Model. Agricultural and Forest Meteorology, 91, 89-111.

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