07 Mar 2022
07 Mar 2022
Status: a revised version of this preprint is currently under review for the journal ANGEO.

On the colour of noctilucent clouds

Anna Lange1, Gerd Baumgarten2, Alexei Rozanov3, and Christian von Savigny1 Anna Lange et al.
  • 1Institute of Physics, University of Greifswald, Felix-Hausdorff-Str. 6, 17487 Greifswald, Germany
  • 2Leibniz-Institute of Atmospheric Physics at the University of Rostock, Schlossstraße 6, 18225 Kühlungsborn, Germany
  • 3Institute of Environmental Physics, University of Bremen, Otto-Hahn-Allee 1, 27359 Bremen, Germany

Abstract. The high-latitude phenomenon of noctilucent clouds (NLCs) is characterised by a silvery-blue or pale blue colour. In this study, we employ the radiative transfer model SCIATRAN to simulate spectra of solar radiation scattered by NLCs for a ground-based observer and assuming spherical NLC particles. To determine the resulting colours of NLCs in an objective way, the CIE (International Commission on Illumination) colour matching functions and chromaticity values are used. Different processes and parameters potentially affecting the colour of NLCs are investigated, i.e., the size of the NLC particles, the abundance of middle atmospheric O3 and the importance of multiply scattered solar radiation. We affirm previous research indicating that solar radiation absorption in the O3 Chappuis bands can have a significant effect on the colour of the NLCs. A new result of this study is that for sufficiently large NLC optical depths and for specific viewing geometries, O3 plays only a minor role for the blueish colour of NLCs. The simulations also show that the size of the NLC particles affects the colour of the clouds. Cloud particles of unrealistically large sizes can lead to a reddish colour. Furthermore, the simulations show that the contribution of multiple scattering to the total scattering is only of minor importance, providing additional justification for the earlier studies on this topic, which were all based on the single scattering approximation.

Anna Lange et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on angeo-2022-10', Anonymous Referee #1, 08 Apr 2022
  • RC2: 'Comment on angeo-2022-10', Anonymous Referee #2, 18 Apr 2022

Anna Lange et al.

Anna Lange et al.


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Short summary
We investigate the influence of different parameters on the colour of noctilucent clouds (highest clouds in the atmosphere), using radiative transfer calculations. We determined the effect of the particle size, optical depth, single scattering/multiple scattering and ozone. For sufficiently large optical depth and for specific viewing geometries, ozone plays only a minor role for the blueish colour of noctilucent clouds (new result).