Explaining the green volcanic sunsets after the 1883 eruption of Krakatoa

Volcanic sunsets are usually associated with extended and enhanced reddish colours typically complemented by purple colours at higher elevations. However, many eyewitnesses reported remarkably clear and distinct green twilight colours after the eruption of Krakatoa (Sunda Strait, Indonesia) in 1883....

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Bibliographic Details
Published in:Atmospheric chemistry and physics 2024-02, Vol.24 (4), p.2415-2422
Main Authors: von Savigny, Christian, Lange, Anna, Hoffmann, Christoph G, Rozanov, Alexei
Format: Article
Language:English
Subjects:
Aerosol optical depth
Aerosols
Approximation
Eruptions
Geometry
Optical analysis
Optical thickness
Ozone
Parameter sensitivity
Parameters
Particle size
Particle size distribution
Radiation
Radiative transfer
Simulation
Size distribution
Stratosphere
Stratospheric sulfate
Sulfate aerosols
Sulfates
Sunset
Twilight
Volcanic aerosols
Volcanoes
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Summary:Volcanic sunsets are usually associated with extended and enhanced reddish colours typically complemented by purple colours at higher elevations. However, many eyewitnesses reported remarkably clear and distinct green twilight colours after the eruption of Krakatoa (Sunda Strait, Indonesia) in 1883. To the best of our knowledge, no earlier studies exist providing an explanation for this unusual phenomenon. In the current work, we employ simulations with the SCIATRAN radiative transfer model to investigate the processes leading to green volcanic sunsets. Green sunsets can be simulated based on plausible assumptions by anomalous scattering on stratospheric sulfate aerosols. We investigate the sensitivity of the twilight colours to relevant parameters such as aerosol optical depth (AOD), the parameters of the particle size distribution (PSD), and the amount of ozone. The main requirements for the occurrence of green twilights are a sufficiently large aerosol optical depth combined with particle radii of about 500–700 nm (assuming stratospheric sulfate aerosols) and a preferably narrow aerosol particle size distribution. The occurrence of green twilights after historic eruptions provides important constraints on the particle size of volcanic aerosols.
ISSN:1680-7324
1680-7316
1680-7324
DOI:10.5194/acp-24-2415-2024