An Accurate Shortwave Gaseous Transmittance Scheme Using Modified Alternate Mapping Correlated K-Distribution Method

Abstract

This paper introduces a newly developed shortwave gaseous transmittance scheme, essentially for rapid atmospheric radiation models. It quantifies the absorption and scattering properties of gases in radiation, highlighting the crucial balance between accuracy and efficiency that affects model performance. The proposed scheme builds on the alternate mapping correlated K-distribution method. A more efficient algorithm is implemented, which reduces the need for manual intervention in determining the number of subintervals required for pseudo-monochromatic calculations in the gaseous transmittance scheme. We propose a variant alternate mapping method, that restores the monotonicity of Rayleigh scattering in the cumulative probability space after extracting strong absorption wavenumbers. This modification improves the accuracy of the simulated upward radiation flux in visible bands. Additionally, by incorporating a wider range of atmospheric profiles into the optimization of the gas-optics look-up table, our scheme demonstrates improved generalization capability. Moreover, we offer a clear physical interpretation of the optimization process. Evaluations using realistic profiles from the Correlated K-Distribution Model Inter-Comparison Project demonstrate that our shortwave gaseous transmittance scheme, which requires only 80 pseudo-monochromatic spectral points, offers significant advantages in calculating radiation flux and heating rates across various scenarios.