The importance of solar illumination for discrete and diffuse aurora
We present a comprehensive overview of the occurrence of discrete and diffuse aurora in the nightside Northern Hemisphere at invariant latitudes 55°-75°. Twenty-one months of Freja observations (1 January 1993 to 30 September 1994) from the Northern Hemi...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2005-12-01
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| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/23/3481/2005/angeo-23-3481-2005.pdf |
| Summary: | We present a comprehensive overview of the occurrence of discrete
and diffuse aurora in the nightside Northern Hemisphere at invariant
latitudes 55°-75°. Twenty-one months
of Freja observations (1 January 1993 to 30 September 1994) from
the Northern Hemisphere, obtained at altitude, are
included in this investigation. We investigate the importance of
seasonal effects, solar illumination and geomagnetic activity for
the auroral precipitation. The seasonal variations in the occurrence
of discrete aurora are separated from the dependence on solar
illumination of the ionosphere. When the effects of sunlight are
eliminated, aurora is found to be more common during the summer.
The occurrence of diffuse, as well as discrete aurora, is suppressed
by solar illumination of the ionosphere. This dependence of diffuse
auroral precipitation on ionospheric conditions is not predicted by
theories that attribute diffuse aurora to equatorial pitch-angle
diffusion of hot magnetospheric electrons. |
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| ISSN: | 0992-7689 1432-0576 |