Topside optical view of the dayside cleft aurora

Photometers on the ISIS-II spacecraft provide a view of the atomic oxygen 5577 and 6300 Å emissions and the $\text{N}{}_2{}^{\mathrm{+}}\text{3914}\text{A}\text{?}$ emission detected as dayside aurora in the magnetospheric cleft region. The 6300 Å emission forms a continuous and permanent band across the noon sector, at about 78° invariant latitude, with a defined region of maximum intensity that is never less than 2kR (uncorrected for albedo), and is centred near magnetic noon. There are significant differences in the intensity patterns on either side of noon and their responses to geomagnetic activity. Discrete 3914 Å auroral forms appear within this region, at preferred locations that cannot be precisely specified, but which tend to the poleward edge of the 6300 Å emission in the evening, and the equatorward edge in the morning where the difference between the two emissions is greatest. It is concluded that the discrete auroras observed by all-sky cameras in the day sector do follow the 6300 Å emission through the cleft region, though a definite cleft boundary is not defined. Substantial 6300 Å emission having a peak intensity near noon is also seen in the low latitude “outer auroral belt”, while the diffuse 3914 Å emission tends to show a relative minimum near noon. On the morning side the 3914 Å intensity is displaced to lower latitude and earlier local times, compared to the 6300 Å emission.