LAUSR

This paper analyzes the role of the outer ionosphere in the occurrence of a large difference in the frequency of accelerated electron fluxes in the auroral region in the premidnight sector for winter and summer conditions, which are associated with discrete auroras. Simulation indicates that the critical value JEIC of the longitudinal current of the Alfvén wave for the development of electrostatic ion–cyclotron instability at heights around the Earth’s radius (h ~ RE) for winter almost coincides with the upper limit of average values of the stationary large-scale longitudinal current. Therefore, weak fluctuations of the longitudinal current associated with the Alfvén wave are sufficient in winter for the development of processes leading to accelerated electron fluxes, which are associated with discrete auroras. The summer value of JEIC is four to five times higher than that for winter, and a stimulated precipitation of auroral electrons is likely to be possible only at high geomagnetic activity. The winter/summer asymmetry in the JEIC value is mainly associated with specific changes in the parameters of the outer ionosphere along the geomagnetic field. The difference in electron density reaches a maximum at heights h ~ RE, where the summer values of this density are five to six times higher than the winter ones, which, in turn, is associated with higher summer temperatures of electrons and ions. The important role of these temperatures in the winter/summer asymmetry in the frequency of accelerated electrons has been noted, it would seem, for the first time.