Abstract
In recent years Barbier and Roach, with collaborators, have observed, during times of strong magnetic activity, intense (though still invisible) emission of the [O I] red lines, λ 6300–6364 A, well to the equatorward side of active auroral displays. The emission comes from a region between 300 and 500 km in altitude, extending over several hundred kilometers in latitude and several thousand kilometers in longitude. It is, in general, separated from the main body of auroral luminosity, and within it the other prominent auroral and airglow emissions, such as [O I], λ 5577 A; N2+, λ 3914 A; and Na, λ 5893 A, are not measurably enhanced. The emission persists over several hours with sluggish geographical movements and slow changes in intensity, in contrast with the more dynamic and kaleidoscopic nature of visual auroras.
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