SOME OBSERVATIONS OF PREDAWN ENHANCEMENT OF RED LINE AIRGLOW OVER GREAT BRITAIN

Zenith and azimuthal photometric observations of the red line of atomic oxygen predawn enhancement are presented which were made in the years 1965-1968 at Sidmouth, Devon and Earlyburn, Peebleshire, both in the U.K. The measurements indicate that the enhancement is a regular occurrence, at least up to geomagnetic latitude 59.5°N in the manner reported from lower latitudes. The onset time shows a solar cycle, seasonal and irregular variation. Evidence is presented to suggest that the long period variations are related to thermopause temperature and the solar EUV interrsity. Heights of emission are deduced from the azimuthal measurements which are mostly in the region 250-300 km, and there is a trend towards increasing height with increasing thermopause temperature. © 1969.