JULES
RADIATION
Surface albedos are specified either as single values for all bands with diagnosed snow albedos or spectral values with prognostic snow albedos.
All-band albedos
Bare soil albedos vary geographically with soil colour. Snow aging is represented by reducing the snow albedo when surface temperature exceeds –2 C
Spectral albedos
The Sellers (1985) two-stream canopy radiation model is used for vegetation albedos in the optional spectral albedo scheme. Separate direct-beam and diffuse albedos in visible and near-infrared wave bands are calculated for each vegetation type.
Snow albedos are calculated using a simplification of the Marshall (1989) parametrization of the Wiscombe and Warren (1980) spectral snow albedo model. The aging of snow is characterized by introducing a prognostic grain size, set to a minimum value for fresh snow and limited to a maximum value.
References
Marshall, S. E., 1989: A physical parametrization of snow albedo for use in climate models. NCAR Cooperative Thesis 123, National Center for Atmospheric Research, Boulder, Co.
Sellers, P. J., 1985: Canopy reflectance, photosynthesis and transpiration. Int. J. Remote Sens., 6(8), 1335-1372
Wiscombe, W. J., and S. G. Warren, 1980: A model for the spectral albedo of snow. I. Pure snow. J. Atmos. Sci., 37, 2712{2733. 24
