Regional Evolution of the Meteosat Solar and Infrared Spectra (2005-2024) Linked to Cloud Cover and Ocean Surface

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Abstract
In this paper we analyze the evolution of atmospheric and surface physical properties on that portion of the Earth covered by the Meteosat Second Generation (MSG) satellites over a period of 20 years (from 2005 to 2024). The radiances show significant changes over time in the solar (–1.3 %) and infrared (+0.4%) domains, consistent with data from similar radiometers (e.g. CERES) on other satellite platforms. The outgoing solar radiance (OSR) mainly decreases as a result of low-level cloud reduction in the nominal Meteosat (at 0° longitude) field of view (MFoV) in the geostationary orbit. The increased CO2 content in the atmosphere also plays a decisive role in the radiation imbalance at the top of the atmosphere (ToA). For 60 MFoV subareas we describe regional changes in the cloud amount at high and low levels in the atmosphere, and show the connection between the imbalance at the ToA and the observed variation in the sea surface temperature (SST) in the Atlantic. We also did not find any significant cirrus variation in the study period. Our study provides a better spectral resolution in its conclusions compared with other analyses, such as those of CERES. It also introduces the SST as a major representative of the climate. For example, the radiance values in the atmospheric split window measurements around 11 µm can be used as a proxy for the humidity column at low levels, a key variable in climate projections, which shows a decadal increase. Meteosat data suggests a so-far unpredictable contribution to climate from the deep ocean and its heat reserve. The recent decrease in the total cloud cover (TCC) at low levels in the MFoV is also validated by the ECMWF ERA-5 reanalysis.

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