Perturbation Method for Solar/Infrared Radiative Transfer in a Scattering Medium with Vertical Inhomogeneity in Internal Optical Properties

Abstract

A new scheme based on perturbation method is presented to solve the problem of solar/ infrared radiative transfer (SRT/IRT) in a scattering medium, in which the inherent optical properties (IOPs) are vertically inhomogeneous. The Eddington approximation for SRTand the two-stream approximation for IRT are used as the zeroth-order solution, and multiple-scattering effect of inhomogeneous IOPs is included in the first-order solution. Observations show that the stratocumulus clouds are vertically inhomogeneous, and the accuracy of SRT/ IRT for stratocumulus clouds by different solutions is evaluated. In the spectral band of 0.25 – 0.69 μ m, the relative error in absorption with inhomogeneous SRT solution is 1.4% at most, but with the homogeneous SRT solution, it can be up to 7.4%. In the spectral band of 5 – 8 μ m, the maximum relative error of downward emissivity can reach (cid:1) 11% for the homogeneous IRTsolution but only (cid:1) 2% for the inhomogeneous IRTsolution.