Extending the KLIMA Radiative Transfer Model to Cloudy Atmospheres: Towards an All-Sky Analysis of FORUM
Year: 2026
Authors: Butali E., Del Bianco S., Cortesi U., Di Natale G., Ridolfi M.
Autors Affiliation: Scuola Univ Super Pavia, PhD Program Sustainable Dev & Global Change Earth, I-27100 Pavia, Italy; Natl Res Council Italy CNR, Inst BioEcon IBE, I-50145 Florence, Italy; Natl Res Council Italy CNR, Inst Appl Phys Nello Carrara IFAC, I-50019 Florence, Italy; Natl Res Council Italy CNR, Natl Inst Opt INO, I-50019 Florence, Italy.
Abstract: Highlights What are the main findings’ KLIMA, a physically based FORTRAN line-by-line radiative transfer model, and the fast radiative transfer model SIGMA exhibit good agreement in cloudy-sky simulations when the same cloud scattering parametrization (Chou approximation) is adopted in both models. The agreement previously observed under clear-sky conditions is therefore largely preserved in the presence of liquid-water and ice clouds, particularly when both models employ a consistent atmospheric path length. What are the implications of the main findings’ The applicability of KLIMA is extended from clear-sky to all-sky radiative transfer simulations. This mixed modeling approach enables different levels of computational efficiency and accuracy: high accuracy in clear-sky conditions, efficient simulations in cloudy atmospheres.Highlights What are the main findings’ KLIMA, a physically based FORTRAN line-by-line radiative transfer model, and the fast radiative transfer model SIGMA exhibit good agreement in cloudy-sky simulations when the same cloud scattering parametrization (Chou approximation) is adopted in both models. The agreement previously observed under clear-sky conditions is therefore largely preserved in the presence of liquid-water and ice clouds, particularly when both models employ a consistent atmospheric path length. What are the implications of the main findings’ The applicability of KLIMA is extended from clear-sky to all-sky radiative transfer simulations. This mixed modeling approach enables different levels of computational efficiency and accuracy: high accuracy in clear-sky conditions, efficient simulations in cloudy atmospheres.Abstract In recent times, increasing attention has been devoted to the investigation of atmospheric processes through remote sensing in order to improve our understanding of climate dynamics and atmospheric physics. This requires accurate simulation of the spectra emitted by the Earth, from which atmospheric composition and thermodynamic conditions can be retrieved. The FORUM mission focuses on observations of the Earth’s outgoing radiation in the far-infrared spectral region, which has been only sparsely explored due to observational challenges, despite its significant contribution to the characterization of atmospheric processes. As part of the mission activities, dedicated simulations of the measurements expected from the FORUM instrument are required. Different models and codes can be employed for this purpose. Fast radiative transfer models, such as SIGMA-FORUM, efficiently simulate all-sky conditions, whereas detailed line-by-line models, such as KLIMA, have generally been limited to clear-sky applications. In this context, SIGMA-FORUM, an all-sky fast radiative transfer model operating in the 10-2760 cm-1 spectral range and KLIMA, a FORTRAN-based line-by-line algorithm extensively validated under clear-sky conditions, are used to simulate FORUM radiances in both clear and cloudy atmospheres. This study extends the comparison between SIGMA-IASI/F2N and KLIMA to cloudy-sky scenarios by incorporating cloud optical properties into KLIMA using the same parametrization approach adopted in SIGMA-FORUM version 2.4. By combining complementary modeling approaches, this work enables KLIMA to simulate atmospheric radiances under all-sky conditions, thereby broadening its applicability.
Journal/Review: REMOTE SENSING
Volume: 18 (6) Pages from: 960-1 to: 960-17
More Information: This research was funded by the Italian Space Agency (ASI), FIT-FORUM project. Part of the research activities described in this paper were carried out with the contribution of the Next Generation EU funds within the National Recovery and Resilience Plan (PNRR), Mission 4-Education and Research, Component 2-From Research to Business (M4C2), Investment Line 3.1-Strengthening and creation of Research Infrastructures, Project IR0000038-Earth Moon Mars (EMM). EMM is led by INAF in partnership with ASI and CNR. The EMM research activities described in this paper were coordinated and executed by CNR.KeyWords: remote sensing; KLIMA model; all sky conditions; FORUM mission; cloud simulation; radiative transfer; cloud propertiesDOI: 10.3390/rs18060960
