Sky background measurements in the 4800-5800-A region at the latitude of the polar cleft.
On the longitude of Scandinavia the dayside auroral emissions within the polar cleft can be measured continuously in midwinter. The intensity of the Rayleigh scattered sunlight is measured to be about 100 R/A at 4860 A when the solar depression angle is 10 degrees and increases rapidly with decreasing solar depression angle. The effect of scattering vanishes around 14 degrees solar depression angle, and the intensity of the sky background can be as low as 2 R/A or 3 R/A. Absolute measurements of auroral emissions for smaller so depression angles than 14 degrees require separate observations of the sky background.
Henriksen
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K
Holbak
B
B
Witt
G
G