ELF emissions observed near the plasmapause and plasma sheet

Alouette 2 VLF data often show broad-band ELF emissions in the invariant latitude range 50°–80° N. These emissions have maximum intensity over a region several degrees in width. The occurrence of these emissions is shown to be related to the period of Pi2 micropulsations, to the plasma-sheet inner boundary and also, during increased magnetic activity, to the plasmapause. This result is consistent with a prediction of Saito and Sakurai (1970) that the plasma-sheet inner boundary comes close to the plasmapause when K p ≥ 2 0.