Aurora on the dayside of the earth observed under especially favorable viewing conditions by the scanning auroral photometer on the ISIS‐2 satellite show several distinctive features. (1) Usually, but not always, a gap or discontinuity in the 5577Å aurora is present through the 10.5 ‐ 12.5 MLT sector, in the same region where the 6300Å aurora typically reaches a maximum. Weak 3914Å emission smoothly fills this gap in most of the passes. (2) A persistent auroral intensity enhancement occurs between 14 and 16 MLT, which is probably related to a statistically deduced maximum in particle fluxes observed in this sector. (3) Aurora in the morning sector at these wavelengths is wider and the poleward boundary is more irregular than in the afternoon.
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Cogger et al. (1977) studied this question.
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