Adjoint perturbation and selection rule methods for solar broadband two-stream fluxes in multi-layer media

Philip Gabriel, Graeme L. Stephens, Ian L. Wittmeyer
2000 Journal of Quantitative Spectroscopy and Radiative Transfer  
This paper describes computationally e$cient methods of solving the two-stream plane-parallel equation of radiative transfer in multi-layered media using adjoint perturbations in combination with selection rules. Semi-analytical results are obtained for the perturbed #uxes in atmospheres illuminated by solar radiation. The perturbation approach is useful in media dominated by multiple scattering whereas selection rules apply when absorption is dominant or if the media is weakly scattering.
more » ... tion rules can be applied with conventional two-stream solvers to reduce the number of radiative transfer calculations. For example, clear sky broadband #uxes computed with selection rules for a 30 layer atmosphere using the k-distribution method were obtained in about one-seventh the time taken by the standard solvers. An 12-fold increase in computational speed over the standard solvers was achieved when selection rules were used with the perturbation method for the same atmosphere. Fluxes so computed were within 10% of those calculated using standard, full up two-stream radiative transfer codes.
doi:10.1016/s0022-4073(99)00137-5 fatcat:w4r2mspq6vfzngiyytcomvkm4q