Satellite observations of energetic heavy ions during a geomagnetic storm

Abstract

Large fluxes of energetic heavy ions (M / q ≈ 16) were observed in the inner magnetosphere during the geomagnetic storm of December 17, 1971. The observations were made by a set of energetic-ion mass spectrometers covering the energy range 0.7–12 kev on board the polar-orbiting satellite 1971-089A (800-km altitude, ≈0300 LT). Significant heavy-ion fluxes were observed for a period of approximately 48 hours during the main phase of the storm. The heavy-ion fluxes frequently exceeded the proton fluxes in the 0.7- to 12-kev energy range. The heavy-ion spectrums were highly variable and frequently contained a peak of several kev. The heavy ions were observed over a wide latitudinal range (2.4 ≲ L ≲ 9) and generally extended to somewhat lower latitudes than the protons. The peak energy flux of these ions was approximately 0.4 erg/cm² sec ster, which is substantial in terms of expected observable ionospheric effects. They may also contribute significantly to the storm-time magnetic-field depression (Dst), since at the same flux they represent an energy density greater by a factor of 4 than that of the protons.