360° panoramic view (Figure 1)

The following pictures show a simulated 360° panoramic view of the sky under different aerosol conditions. The images were calculated with the libRadtran radiative transfer package using the "output rgb" option where the radiances are automatically converted to red, green, and blue values. For a description of the algorithm please see Mayer and Emde, Atmospheric Research, in press, 2007.
The calculations were done for a location 52.95°N, 1.12°E for June 23. The viewing direction is South. The horizontal axis is from -180° to +180° azimuth. The vertical axis is from 90° to 0° solar zenith angle.
For all calculations including aerosol the libRadtran default aerosol according to Shettle [1989] was selected: rural, spring-summer, visibility 50km. In addition, the four volcanic scenarios by Shettle [1989] were used: background, moderate, high, extreme.
For the static images the solar zenith angle was 80° - close to sunrise. Please move the mouse over an image to view the diurnal variation.
clean clean, aerosol-free conditions
In a pure Rayleigh atmosphere in absence of aerosol the location of the sun is not visible at all (in reality, the direct sun is of course visible but the diffuse radiance carries no indication of the location of the sun)
background volcanic background conditions; boundary layer horizontal visibility 50km
The location of the sun is clearly visible due to the forward scattering by aerosols which causes an aureole around the sun. Please note that in the volcanic background case most scattering is due to the boundary layer aerosol which was assumed constant for all four cases.
moderate moderate volcanic conditions; boundary layer horizontal visibility 50km
high high volcanic conditions; boundary layer horizontal visibility 50km
extreme extreme volcanic conditions; boundary layer horizontal visibility 50km
With increasing stratospheric aerosol load the aureole becomes stronger and the sky close to the sun becomes more and more red; nevertheless the color is still dominated by blue because the larger fraction of the sky is still blue. For a completely red sky we probably need broken clouds.
This 360° panoramic view is probably not what a painter would paint. Please click here to get the image, as seen by a 35 mm camera with 28mm focal length ("Kleinbildkamera mit 28mm Brennweite").

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