Reflexion of High Frequencies during Auroral Activity

Abstract

VERTICAL incidence measurements of the ionosphere at 17.31 Mc./s. usually elicit no reflexions except when meteoric ionization is present, and then the reflexions persist for a minute or two. Recently, however, we have observed enduring reflexions at this frequency during periods of auroral activity. The returns show large slant ranges, probably indicating that the centres of reflexion are at a considerable horizontal distance rather than at great heights. The ionization responsible for the reflexions must exceed 3.7 × 10⁶ electrons/cm.³ in order to be observed at this frequency. Somewhat similar echoes from aurora borealis have been reported by Lovell, Clegg and Ellyett¹ using transmissions on 46 Mc./s. Also, ultrahigh-frequency long-distance transmission during auroral storms has aroused considerable interest in amateur radio circles².