Morphology of electron concentration enhancement at a height of 1000 kilometers at polar latitudes

A study based on Alouette 1 data of electron concentration enhancement at a height of 1000 km at polar latitudes during 1962–1964 is presented. The major features are (1) Enhancement occurs in three apparently independent concentric zones, zones 1, 2, and 3. Zone 1 includes the area with invariant latitudes higher than about 80°. The upper boundaries of zones 2 and 3 are, respectively, at approximately 80° and 73° at magnetic noon and at somewhat lower latitudes at magnetic midnight. The extent or width of each zone varies with season and magnetic activity, and within each zone enhancement occurs sporadically in space and time. (2) Enhancement occurs with maximum frequency at different magnetic local times in each zone. Occurrence frequencies and amplitudes are subject to magnetic local time, seasonal and magnetic activity effects. The latter two effects on occurrence frequency are especially notable in zones 1 and 3. It is suggested that the enhancement is caused by particle ionization due to precipitation of low-energy electrons (E < 1 kev).