Geographic distribution ofF-region electrons with about 10-ev energy

Abstract

Large fluxes of about 10-ev electrons with magnitude in the range of 1010–1031 cm−2 sec−1 have been measured by a retarding potential analyzer mounted on an oriented satellite. The restricted geographic locations and altitudes at which the large fluxes were observed suggest that the fluxes are produced by the interaction of radiation belt particles with the upper atmosphere. Two regions of intense electron flux occurred at approximately L = 1.1 in the southern hemisphere at an altitude of 270 km with maxima at 90°W and 110°E. The maximum at 90°W is presumed to be produced by more energetic electrons drifting eastward at the bottom of the inner radiation belt and interacting with the atmosphere. Maximum energy flux observed within the instrumental energy window was 1 erg/cm² sec. Enhanced ambient electron concentration, ion temperature, and negative vehicle potential accompanied the large electron flux. A local electron temperature of 20,000°K would explain the observed vehicle potential and electron flux. The measured ion temperature in the maximum was of the order of 1000°K above expected neutral temperatures and measured ion temperature on either side. A less intense but still distinct region of electron flux was evident at about L = 1.7 in the southern hemisphere at 130° west longitude. This region, also characterized by enhanced ion temperature and electron concentration, is presumed to be produced by inner radiation belt electrons at the center of the belt interacting with the atmosphere. A region of intense electron flux occurred over Siberia with center at about 60°N and 90°E and at an altitude of 270 km. The maximum occurred at about L = 3.6, which is approximately the center of the outer radiation belt; the longitude of the maximum is that at which the mirror altitude of a particle drifting around the earth is largest. Energy flux within the instrumental energy window was 0.25 erg/cm² sec at the center of the region. A relative minimum in electron concentration and maximum in negative vehicle potential accompanied this maximum in electron flux. Results of this study suggest that ionization produced at L = 1.1 by energetic particles may contribute to the ionospheric equatorial magnetic anomaly. Interaction of inner radiation belt electrons with the atmosphere west of the South Atlantic magnetic anomaly produces a knob or knobs of electron concentration there with maximum concentration between 90 and 180°W longitude. Maximum ionization produced by the interaction is about 3 × 105 cm−3.