ELECTRON DENSITIES OF 8–100 ELECTRONS CM−3 DEDUCED FROM ALOUETTE II HIGH-LATITUDE IONOGRAMS

Abstract

Alouette II topside ionograms recorded at high latitudes (L ≈ 6 or greater) and high altitudes (1 500–3 000 km) show an interference pattern between the electron gyro and the electron hybrid resonance spikes, when the electron density at the satellite is very low.This interference pattern can be used to determine the electron number density at the satellite, to an accuracy of better than 10% when the electron density is less than about 100 electrons cm−3. Preliminary results show that electron densities less than 30 electrons cm−3 occur over the region north of about 60 °N. geomagnetic latitude and that the southern boundary of the region where the very low electron densities are observed shifts south by about 8° between noon and midnight.