HR: 0800h
AN: B51C-0228    [Abstracts]
TI: Leaf-to-Canopy Scaling of Carbon, Energy, and Moisture Fluxes in the Simple Biosphere Model (SiB)
AU: * Baker, I T
EM: baker@atmos.colostate.edu
AF: Department of Atmospheric Science, Colorado State University Foothills Campus 1371 Campus Delivery, Fort Collins, CO 80523-1375 United States
AU: Zupanski, D
EM: zupanski@cira.colostate.edu
AF: Cooperative Institute for Research in the Atmosphere, Colorado State University Foothills Campus 1375 Campus Delivery, Fort Collins, CO 80523-1375 United States
AU: Prihodko, L
EM: lara@atmos.colostate.edu
AF: Department of Atmospheric Science, Colorado State University Foothills Campus 1371 Campus Delivery, Fort Collins, CO 80523-1375 United States
AU: Schaefer, K
EM: kevin@atmos.colostate.edu
AF: Climate Monitoring and Diagnostics Laboratory, National Oceanographic and Atmospheric Administration 325 Broadway, Boulder, CO 80305 United States
AU: Berry, J
EM: joeberry@globalecology.stanford.edu
AF: Department of Global Ecology, Carnegie Institute of Washington 260 Panama Street, Stanford, CA 94305-1297 United States
AU: Denning, A S
EM: denning@atmos.colostate.edu
AF: Department of Atmospheric Science, Colorado State University Foothills Campus 1371 Campus Delivery, Fort Collins, CO 80523-1375 United States
AB: The Simple Biosphere Model (SiB) has traditionally calculated photosynthesis for a single sun-leaf and used an empirical adjustment to extinction law in conjunction with satellite information to adjust carbon flux up to the canopy scale. This 'big leaf' approach has several limitations: modeled photosynthesis reaches light saturation too soon, and modeled Bowen Ratio has typically been too high. We have modified the SiB radiative submodel to simulate radiation balance and photosynthesis for sunlit and shaded leaves in SiB's fully prognostic canopy air space. The leaf-to-canopy scaling is based upon the partitioning of sunlit and shaded leaves, which is determined by canopy type and solar zenith angle. This presents a radical departure from the 'big leaf' radiative submodel used in the past. As a result of these fundamental changes to the model, we found that certain aspects of model parameterization require updating. For example, SiB photosynthesis is limited by the minimum of three assimilation rates: 1) efficiency of the photosynthetic enzyme system, 2) light limitation, and 3) export of photosynthesis products. These rates are not co-limited in individual leaves, but the transition has been shown to be smooth on the canopy scale. Therefore, we have used Maximum Likelihood Ensemble Filter (MLEF) techniques to determine optimum values for co-limitation parameters used in SiB. MLEF was developed at Colorado State University, and is designed to calculate optimal estimates of initial conditions, model errors, and empirical parameters, and also uncertainties of these estimates. The optimal estimates are defined as maximum likelihood values, obtained as results of the minimization of a cost function. The uncertainties are defined in terms of analysis and forecast error covariance matrices, calculated in ensemble-spanned subspace. We apply MLEF techniques to SiB parameters at several flux tower sites to determine if there are uniform modifications to established SiB parameters when the sunlit/shaded radiation submodel is applied.
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 1615 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 4805, 4912)
DE: 1631 Land/atmosphere interactions (1218, 1843, 3322)
DE: 3315 Data assimilation
SC: Biogeosciences [B]
MN: Fall Meeting 2005