Backscatter from a postulated plasma instability in the polar cap ionosphere and the direct measurement of a horizontal E region current

Previously published data by L. J. Cahill, Jr., from a rocket measurement of a horizontal polar E region sheet current have been further analyzed by using nearby ground-based magnetograms and ionograms. The combined data indicate that the requirements of the Farley-Buneman two-stream instability were fulfilled and give further support to the hypothesis that a plasma instability is revealed by the so-called 'slant E condition' on the ionograms previously described.