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Outline

Outline. Approach Data sets PAR fPAR C4/C3 LUE optimization. Approach. GPP = LUE × APAR = LUE × fPAR × PAR PAR = SW × R PB C4 and C3 LUE and fPAR algorithm. Data set: Ameriflux Site.

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Outline

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  1. Outline • Approach • Data sets • PAR • fPAR • C4/C3 • LUE optimization

  2. Approach • GPP = LUE × APAR = LUE × fPAR× PAR • PAR = SW × RPB • C4 and C3 LUE and fPAR algorithm

  3. Data set: AmerifluxSite • Ameriflux GPP observations were used to minimize the discrepancy between modeled and observed GPP • Sites with more than one year data during 2004 to 2006 were chosen • Monthly GPP calculated from half-hourly GPP fluxes

  4. Data set: fPAR products • EVI/NDVI-derived fPAR • Monthly EVI/NDVI 2004-2006 • Original: 0.05 deg • Used in model: 0.5 deg • MODIS fPAR • Monthly MODIS fPAR 2004-2006 • Original: 0.05 deg • Used in model: 0.5 deg • SeaWifsfPAR • Monthly, 2004-2006 Jan – June • Last 6 months were restructured by monthly mean from previous years • Original: 0.25 deg • Used in model: 0.5deg

  5. Data set: radiation • GEOS-5 surface net shortwave radiation and surface albedo • 3-hourly; 2004 – 2006; 2×2.5 deg • SRB PAR and SW • Monthly; 2004-2006; 1 deg • CERES PAR and SW • Monthly; 2004-2005; 1 deg • BSRN measured SW • Monthly; 2004-2005

  6. Data set: C4 distribution • Global C4 percentage • 1 deg • Africa C4 percentage • 1 km

  7. EVI/NDVI-derived fPAR • Area distribution of global EVI according to biome types • Linear function applied to covert EVI/NDVI to fPAR • Upper bound: top 25% EVI of topical rainforest • Lower bound: EVI in Sahara desert with annual rainfall less than 25 mm

  8. PAR • Adjustment for GEOS-5 shortwave radiation • Downward SW = net SW / ( 1 - albedo ) • Ratio of SRB SW to GEOS SW • Conversion from shortwave radiation to PAR • Ratio of SRB PAR to SRB SW • High temporal resolution PAR using GEOS-5 adjusted SW

  9. APAR = PAR × fAPR

  10. C4 photosynthesis • Algorithm A • Same fPAR for C3 and C4 • Separate APAR according to C3 and C4 spatial distribution • Algorithm B • Allocate most of the fPAR seasonal cycle to C4 • Separate APAR with different fPAR for C3 and C4

  11. C4 LUE • Lobell ratio: • Mean C4 LUE: 0.66 g C/MJ • Mean C3 LUE: 0.29 g C/MJ • Ameriflux ratio: • Cropland rotation sites • Mean C4 GPP/mean C3 GPP = 1.32

  12. LUE optimization • A range of LUE was used to calculate GPP using the paradigm: GPP = LUE × APAR • Just account for monthly GPP from all C3 sites and rotation site with C3 crops • C4 LUE calculated from the Lobell and Ameriflux ratios

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