The E-layer ionization over Sanae during the substorm of 27 July 1979

Electron density profile analysis of ionograms recorded at Sanae, Antarctica, during an event in the early morning of 27 July 1979 revealed the following interesting features: (i) A retardation type sporadic E-layer changing to a particle type, the critical frequency and virtual height of which were relatively constant before the substorm onset. (ii) Sporadic E-layers of the auroral type with very high critical frequencies, reaching 8.3 MHz, and lower virtual heights than before, were recorded during the substorm. These phenomena are consistent with overhead electron precipitation of the auroral type