Conjugate photoelectron impact ionization

Abstract

The exchange of photoelectrons between ionospheres in a matter of minutes rather than at the slow ambipolar speed is discussed. It is shown that the electron density may be affected by secondary processes resulting from the conjugate photoelectron flux but not by the flux itself. The flux spectrum of conjugate photoelectrons throughout the day at the solstices for minimum solar activity is calculated for 55 N° geographic latitude over Europe, using a method previously employed by Nisbet. Summer escaping flux values range up to 9 × 10 12 electrons m −2 sec −1 and winter values to 5 × 10 12 electrons m −2 sec −1. Compared at specific solar zenith angles the computed values are in good agreement with recent satellite measurements. Approximately half of this flux is lost by Coulomb collisions along the field line path. The resulting flux arriving at the local ionosphere produces ionization by inelastic collisions in the atmosphere. This additional ionization is about 3 per cent of the ionization from local processes at summer noon and 48 per cent at winter noon. During winter nighttime this conjugate photoelectron ionization can be significant for several hours. Although small in magnitude, this additional ionization should systematically modify the summer total electron content depending on geographic location. The large seasonal differences in the relative impact ionization may explain in part the F-layer seasonal anomaly. This source may be important for maintaining and causing enhancements in the winter nighttime ionosphere.