Direct Observations of Low-energy Electrons in the Disturbed Ionospheric E-region

Abstract

DIFFERENTIAL spectra of electrons 20–3,000 eV in energy have been directly measured in the ionosphere for the first time. The spectrometer used an open electron multiplier as its detector, counting individual electrons. It was carried in Black Brant II rockets launched in 1963 at Churchill, Manitoba, in the presence of so-called auroral absorption (of very-high-frequency cosmic radio noise). Such absorption events usually last from a few minutes to about an hour, with rapid fluctuations, and occur in or near the auroral zone. Electrons of energy < 100 keV, precipitated into the ionosphere by processes not understood but closely related to magnetic activity, are considered to be the main cause of these events. A great deal of information exists on the upper part of this energy range, but below 10 keV there is very little^1,2. Our experiment covered a large part of this unknown region. In order to provide a more complete spectrum, measurements on electrons above 10 keV were made aboard the same rockets by instruments from the National Research Council of Canada. In addition, experiments measuring electron density and radio-wave propagation effects were carried, the results from which will be discussed in future publications.