Assessing the MTG Flexible Combined Imager Outgoing Longwave Radiation Product Using GERB and CERES Observations

Outgoing longwave radiation (OLR) at the top of the atmosphere is a fundamental component of the Earth’s radiation budget and a key observable for monitoring climate variability and change. The Meteosat Third Generation (MTG) Flexible Combined Imager (FCI) introduces a new geostationary OLR product derived from narrowband thermal infrared radiances using scene-dependent regressions. Ensuring the continuity, stability and scientific usability of this product relative to heritage datasets is therefore essential. Here we present an evaluation of the MTG FCI OLR product using comparisons with the Geostationary Earth Radiation Budget (GERB) thermal fluxes on Meteosat Second Generation (MSG) and with CERES OLR products.

The comparisons against GERB exploit the co-location of MSG and MTG to enable a detailed intercomparison between MTG FCI OLR and GERB thermal fluxes over several months spanning different seasons. Broadscale and regional differences are analysed as a function of viewing geometry, time of day and surface type, and cloud cover, and are interpreted in the context of known limitations in the GERB radiance-to-flux conversion and the MTG OLR retrieval methodology, including the use of scene-dependent regressions and plane-parallel assumptions.

Further comparisons against the CERES SYN GEO hourly and monthly mean fluxes, together with associated cloud information, provide an additional independent benchmark and allow the investigation of cloud-dependent and diurnal characteristics of the MTG OLR product. Together, these results provide a comprehensive assessment of the performance, stability and limitations of the MTG FCI OLR product and offer guidance for its application in studies of the Earth’s radiation budget and climate variability, as well as a roadmap for future product improvements.