Optimized Alternate Mapping Correlated K‐Distribution Method for Atmospheric Longwave Radiative Transfer

Abstract

Radiative transfer models are widely applied in climate models to simulate vertical temperature perturbations caused by external radiative forcings. A large part of radiative transfer models is the infrared gaseous spectral transmittance scheme, which quantifies the longwave atmospheric absorption. A rapid infrared gaseous spectral transmittance scheme, called the Optimized alternate Mapping Correlated K‐Distribution model (OMCKD), is introduced in this paper. To improve the accuracy of our scheme without increasing pseudo‐monochromatic calculations, we introduce the optimal iteration method to automatically tune the equivalent absorption coefficients in the cumulative probability subspace. In addition, a new expression weighted by black‐body radiation is introduced to calculate the equivalent absorption coefficient. The OMCKD simulates heating rate and radiation flux with errors of less than 0.12 K d−1 and 0.35 W m−2, respectively, below stratopause for standard atmospheric profiles. The OMCKD is also evaluated and compared with the rapid radiative transfer model for general circulation models (RRTMG) in realistic atmospheric profiles. We found that OMCKD can accurately produce heating rates and generally captures radiative forcings associated with large perturbations to the concentrations of main greenhouse gases. Furthermore, the number of pseudo‐monochromatic calculations in OMCKD is 11.4% less than that in RRTMG, which indicates less computational cost.

Improvements of the Microwave Gaseous Absorption Scheme Based on Statistical Regression and Its Application to ARMS

“…One is spectral sampling strategies including the Correlated K Distribution method (CKD) (Goody et al, 1989;G. Shi et al, 2009;Cai et al, 2023), the Optimal Spectral Sampling method (OSS) (Moncet et al, 2015) and the Principal Component Analysis method (PCA) (Matricardi, 2010;Havemann et al, 2018;X. Liu et al, 2016;C.…”