Noctilucent Clouds in Daytime: Circumpolar Particulate Layers Near the Summer Mesopause.

Observations with a horizon scanning airglow photometer on OGO-6 have revealed the presence of a dense scattering layer near 80 km over the geographic pole during the local summer. The layer is detected on all satellite passes above 80° latitude beginning 15 days before the solstice. The optical depth of the layer increases by more than a factor of 50 between 70° and 85°. It is suggested that noctilucent clouds are weak sporadic manifestations of these persistent polar layers.