Greifswald 2024 – scientific programme
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UP: Fachverband Umweltphysik
UP 7: Posters
UP 7.1: Poster
Wednesday, February 28, 2024, 16:30–18:30, ELP 6: Foyer
Revisiting the question "Why is the sky blue?" — •Anna Lange1, Alexei Rozanov2, and Christian von Savigny1 — 1Institute of Physics, University of Greifswald, Germany — 2Institute of Environmental Physics, University of Bremen, Germany
The common answer to the question "Why is the sky blue" is usually Rayleigh scattering. In 1953 Edward Hulburt demonstrated, that the blue colour of the zenith sky at sunset is to 1/3 caused by Rayleigh scattering and to 2/3 caused by ozone absorption. In this study, an approach to quantify the contribution of ozone to the blue colour of the sky for different viewing geometries is implemented using the radiative transfer model SCIATRAN and the CIE XYZ colour system. The influence of ozone on the blue colour of the sky is calculated for solar zenith angles of 10°-90° and a wide range of viewing geometries. For small solar zenith angles, the influence of ozone on the blue colour of the sky is minor, as expected. However, the effect of ozone increases with increasing solar zenith angle. The calculations for the Sun at the horizon confirm Hulburt's estimation with remarkably good agreement. More stratospheric aerosols reduce the ozone contribution at and near the zenith for the Sun at the horizon. The exact contribution of ozone depends strongly on the assumed total ozone column. The calculations also show that the contribution of ozone increases with increasing viewing zenith angle and total ozone column. Variations in surface albedo as well as full treatment of polarised radiative transfer were found to have only minor effects on the contribution of ozone to the blue colour of the sky.
Keywords: radiative transfer; ozone absorption; Rayleigh scattering; atmospheric physics and chemistry; blue sky