Articles | Volume 14, issue 11
Atmos. Chem. Phys., 14, 5599–5615, 2014
https://doi.org/10.5194/acp-14-5599-2014
Atmos. Chem. Phys., 14, 5599–5615, 2014
https://doi.org/10.5194/acp-14-5599-2014

Review article 05 Jun 2014

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 T. Fauchez et al.
  • 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).

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