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Article Dans Une Revue Atmospheric Chemistry and Physics Année : 2014

Impact of cirrus clouds heterogeneities on top-of-atmosphere thermal infrared radiation

Résumé

This paper presents a study of the impact of cir-rus cloud heterogeneities on the thermal infrared brightness temperatures at the top of the atmosphere (TOA). Realistic 3-D cirri are generated by a cloud generator based on simplified thermodynamic and dynamic equations and on the control of invariant scale properties. The 3-D thermal infrared radiative transfer is simulated with a Monte Carlo model for three typical spectral bands in the infrared atmospheric window. Comparisons of TOA brightness temperatures resulting from 1-D and 3-D radiative transfer show significant differences for optically thick cirrus (τ > 0.3 at 532 nm) and are mainly due to the plane-parallel approximation (PPA). At the spatial resolution of 1 km × 1 km, two principal parameters control the heterogeneity effects on brightness temperatures: i) the optical thickness standard deviation inside the observation pixel, ii) the brightness temperature contrast between the top of the cirrus and the clear-sky atmosphere. Furthermore, we show that the difference between 1-D and 3-D brightness temperatures increases with the zenith view angle from two to ten times between 0 • and 60 • due to the tilted independent pixel approximation (TIPA).
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hal-01971900 , version 1 (06-09-2020)

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T. Fauchez, C. Cornet, Frédéric Szczap, P. Dubuisson, T. Rosambert. Impact of cirrus clouds heterogeneities on top-of-atmosphere thermal infrared radiation. Atmospheric Chemistry and Physics, 2014, 14 (11), pp.5599-5615. ⟨10.5194/acp-14-5599-2014⟩. ⟨hal-01971900⟩
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