Nighttime ionization by energetic particles at Wallops Island in the altitude region 120 to 200 km

Abstract

Five Nike Apache rockets, each including an energetic particle spectrometer and an electron density‐electron temperature experiment, have been launched from Wallops Island (L = 2.6) near midnight under varying geomagnetic conditions. On the most recent of these (5 January 1978) an additional spectrometer with a broom magnet, and a 391.4 nm photometer were flown. The data from this flight indicate that the energetic particle flux consists predominantly of protons, neutral hydrogen and possibly other energetic nuclei. The energy spectrum becomes much softer and the flux more intense with increasing Kp for 10<E<100 keV. The pitch angle distribution at 180 km is asymmetrical with a peak at 90° indicating that the majority of particles are near their mirroring altitude. Ionization rates are calculated based on the measured energy spectrum and mirror height distribution. The resulting ionization rate profile is found to be nearly constant with altitude in the region 120 to 200 km. The measured energetic particle flux and calculated ionization rate from the five flights are found to vary with magnetic activity (based on the Kp and Dst indexes) in the same way as the independently derived ionization rates deduced from the electron density profile.