An accurate approximation to the diffusivity factor

A new analytical approximation for diffusivity factor has been developed to deal with the angular integration of the diffuse transmission function for infrared radiation. The method is based on the bridging function theory which connects the exact results at both of the transparent and opaque limits. It is shown that the new scheme is much more accurate than any previously proposed schemes. By implemented into a one-dimensional radiative model, it is found that the new diffusivity factor can produce very accurate results in flux and cooling rate in the main spectral ranges for CO2, O3, and H2O. Also, the new proposed diffusivity factor is efficient in computing.Therefore, the new scheme is a proper choice to replace the constant diffusivity factor of 1.66 currently used in radiative transfer models.

► High-efficiency computing integration over the zenith angle.
► Valid for arbitrary optical depth.
► Its accuracy is much better than that of all other existing approximations.
► Bridging technique.