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UP: Fachverband Umweltphysik
UP 1: Clouds in Planetary Atmospheres (joint session EP/UP)
UP 1.3: Vortrag
Dienstag, 21. März 2023, 17:15–17:30, ZEU/0160
On the colour of noctilucent clouds — •Christian von Savigny1, Anna Lange1, Gerd Baumgarten2, and Alexei Rozanov3 — 1Institute of Phyics, University of Greifswald, Greifswald, Germany — 2Leibniz Institute of Atmospheric Physics, Kühlungsborn, Germany — 3Institute of Environmental Physics, University of Bremen, Bremen, Germany
Noctilucent clouds, also known as polar mesospheric clouds, are a polar summer mesopause phenomenon and they are typically characterised by a silvery-blue or pale blue colour. In this contribution, we investigate the reasons for this colour using the radiative transfer model SCIATRAN in combination with the CIE (International Commission on Illumination) colour-matching functions in order to the determine the resulting colour impression in an objective way. 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 confirm earlier studies indicating that absorption of solar radiation in the O3 Chappuis bands can have a significant effect on the colour of the NLCs. It is, however, found that for sufficiently large NLC optical depths O3 plays only a minor role for the blueish colour. The simulations also show that the size of 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.