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Trends in spectrally resolved OLR from 10 years of IASI measurements

par Whitburn, Simon ;Clarisse, Lieven ;Delcloo, Andy;Dewitte, Steven;Bouillon, Marie M.;George, Maya;Safieddine, Sarah;Coheur, Pierre ;Clerbaux, Cathy
Référence IASI 2021 Conference (06-10 December 2021: Evian, France)
Publication Non publié, 2021-12-06

Communication à un colloque

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Résumé :

The Earth’s Outgoing Longwave Radiation (OLR) is a key component in the study of climate. As part of the Earth’s radiation budget, it reflects how the Earth-atmosphere system compensates the incoming solar radiation at the top of the atmosphere. At equilibrium, incoming and outgoing radiation compensate each other on average. Any perturbation of this balance through, for example, a variation of the climate drivers (e.g. rise in greenhouse gases concentration) causes a climate response (e.g. surface temperature increase) which brings the radiation budget back to equilibrium. OLR estimates from dedicated broadband instruments are available since the mid-1970s and have considerably improved our understanding of the Earth-atmosphere system and of its long-term changes. However, such instruments only provide an integrated OLR over a broad spectral range and are therefore not well suited for tracking separately the impact of the different parameters affecting the OLR, making it difficult to identify compensating biases and errors in climate models. Better constraints can be obtained from spectrally resolved OLR (i.e. the integrand of broadband OLR, in units of W m-2 (cm-1)-1) derived from infrared hyperspectral sounders. Recently, we developed an algorithm to derive clear-sky spectrally resolved OLR from measurements made by the IASI sounder on board the Metop satellites at the 0.25 cm-1 native spectral sampling of the L1C spectra (Whitburn et al. 2020). It is based on a set of spectrally resolved angular distribution models (ADMs) developed from synthetic spectral for a large selection of scene types associated with different states of the atmosphere and the surface. Here, we present the retrieval algorithm and evaluate how the derived-OLR compares with other known and widely used datasets such as the CERES and the AIRS integrated and spectral OLR. We then analyze the changes in 10 years (2008-2017) of the spectrally resolved OLR (at the 0.25 cm-1 spectral sampling) and we relate them to known changes in greenhouse gases concentrations (CO2, CH4, H2O, …) and climate phenomena activity such as El Niño-Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO).