Integrated Biosphere Simulator - IBIS Structure

IBIS Structure

The land surface module is based on the land surface transfer model (LSX) package of Thompson and Pollard, and simulates the energy, water, carbon, and momentum balance of the soil-vegetation-atmosphere system. The model represents two vegetation canopies (e.g., trees versus shrubs and grasses), eight soil layers, and three layers of snow (when required). The solar radiative transfer scheme of IBIS-2 has been simplified in comparison with LSX and IBIS-1; sunlit and shaded fractions of the canopies are no longer treated separately. The model now follows the approach of Sellers et al. and Bonan . Infrared radiation is simulated as if each vegetation layer is a semitransparent plane; canopy emissivity depends on foliage density. Another difference between IBIS-2 and IBIS-1 and LSX, is that IBIS-2 uses an empirical linear function of wind speed to estimate turbulent transfer between the soil surface and the lower vegetation canopy, and IBIS-1 and LSX use a logarithmic wind profile. The total evapotranspiration from the land surface is treated as the sum of three water vapor fluxes: evaporation from the soil surface, evaporation of water intercepted by vegetation canopies, and canopy transpiration.

IBIS simulates the variations of heat and moisture in the soil. The eight layers are described in terms of soil temperature, volumetric water content and ice content. All the process occurring in the soil are influenced by the soil texture and amount of organic matter within the soil. One difference from the physiological processes in previous version of the model is that IBIS-1 calculates the maximum Rubisco carboxylation capacity (Vm) by optimizing the net assimilation of carbon by the leaf. IBIS-2 prescribes constant values of Vm for the plant functional typed (PFT). To scale photosynthesis and transpiration from the leaf level to canopy level, IBIS-2 assumes that the net photosynthesis within the canopy is proportional to the APAR within it.

Read more about this topic:  Integrated Biosphere Simulator

Famous quotes containing the word structure:

    With sixty staring me in the face, I have developed inflammation of the sentence structure and definite hardening of the paragraphs.
    James Thurber (1894–1961)