2002 Annual

Thursday, 17 January 2002: 2:00 PM
Simulating Carbon and Energy Exchanges over the Amazonia using a photosynthesis model within SSiB
Dev dutta S. Niyogi, North Carolina State University, Raleigh, NC; and Y. Xue, X. Zhan, and G. J. Collatz
Poster PDF (434.8 kB)
ne of the majors goals of the large scale biosphere experiment in Amazonia (LBA) is to understand the climatological and hydrological functioning of Amazon. We discuss the development of a simplified photosynthesis based vegetation scheme embedded within SSiB, and the initial results of the simulations using this scheme over the Amazonian region. The original vegetation scheme within SSiB followed a diagnostic Jarvis - type stomatal model. Such a scheme by design relies on the prescription of a so - called minimum stomatal resistance, and can simulate limited interactions within the complex ecosystem dynamics. This stomatal scheme was replaced by a semi-analytical stomatal resistance - photosynthesis model with radiation, biochemical (Rubisco), and CO2 based couplings. As that, humidity, rather than CO2 concentration (as in traditional photosynthesis models) is assumed to be a known factor, and six limiting conditions (three each for a C3 or C4 photosynthesis pathway) are analytically balanced to yield gross and net primary productivity. A scaling method, which considers the leaf shading effect, is developed and tested. The biophysical changes in the canopy environment affect the surface environment through CO2, water vapor and heat exchange. Thus a more interactive feedback between the surface, vegetation, atmospheric forcing, and the carbon and hydrological cycles are introduced. We present results from three sets of simulations: first involving the original Jarvis - type scheme, the second related to the semi - analytical photosynthesis scheme, and the third based on shading and radiation attenuation based scaling of the photosynthesis scheme. The model results are compared with tower observations dataset comprising of temperature, humidity, wind, radiation, precipitation, and the fluxes of heat, momentum, and CO2. A comparison of the model results and discussion of the surface - atmosphere exchange as depicted through the photosynthesis and non - photosynthesis pathways is also discussed.

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