Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 14, 5599-5615, 2014
https://doi.org/10.5194/acp-14-5599-2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.
Review article
05 Jun 2014
Impact of cirrus clouds heterogeneities on top-of-atmosphere thermal infrared radiation
T. Fauchez1, C. Cornet1, F Szczap2, P. Dubuisson1, and T. Rosambert2 1Laboratoire d'Optique Atmosphérique, Université Lille 1, Villeneuve d'Ascq, France
2Laboratoire de Météorologie Physique, Université Blaise Pascal, Clermont Ferrand, France
Abstract. This paper presents a study of the impact of cirrus 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).

Citation: Fauchez, T., Cornet, C., Szczap, F., Dubuisson, P., and Rosambert, T.: Impact of cirrus clouds heterogeneities on top-of-atmosphere thermal infrared radiation, Atmos. Chem. Phys., 14, 5599-5615, https://doi.org/10.5194/acp-14-5599-2014, 2014.
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