Phase: RAMI4PILPS
The Joint Research Centre Two-stream (JRC2S) model [Pinty et al., 2006] has been designed to improve on current 1-D formulations implemented in climate models to accurately estimate the fractions of radiation absorbed separately by the vegetation canopy and the underlying background.
Its analytical formulation ensures the correct balance between the scattered, transmitted and absorbed radiation fluxes irrespective of the structural and spatial heterogeneity of the canopy provided that effective values for the model parameters of the vegetation layer are adopted.
The two-stream solutions, as well as their approximations, for estimating the three radiant fluxes are decomposed into separate contributions, namely the Black Background (no scattering from the background), the Black Canopy (no scattering by canopy elements) and the remaining contribution involving multiple scattering events between the canopy and the background.
This decomposition facilitates the identification of the physical processes intervening in the various components.
The Black Background solutions follow Meador and Weaver’s [1980] original two-stream solutions for direct illumination conditions of an atmospheric layer.
It was shown that the latter deliver very accurate results provided they account for the canopy structure factor.
The solution to the Black Canopy problem is accurately represented via an approximate function involving the value of the canopy structure factor estimated at 60 ° Sun zenith angle.
Finally the coupled canopy-background scattering processes are parameterized on the basis of Meador and Weaver’s [1980] two-stream solutions but extended to address the case of an external isotropic source of illumination.
Specific attention was given to limiting the maintenance of the software and the JRC2S can be easily implemented in large-scale host models via the addition of a vertical layer having radiative properties that mimic those from the vegetation-soil canopy system.
