Diurnal and Seasonal Variations of the Energy Spectrum of Precipitating Electrons Derived from Electron Concentration Measurement Data Obtained by the Method of Incoherent Scattering of Radio Waves

Profiles of electron concentration observed by the incoherent scattering facility EISCAT (69.7° N, 19° E) are used to derive the spectral characteristics of energetic electrons precipitating at auroral latitudes and to explore diurnal and seasonal variations of such electrons. It is shown that electrons precipitating in the morning sector have a harder energy spectrum than electrons in the evening sector. At the same time, the total electron flux producing the given level of absorption of cosmic radio waves is higher for daytime invasions than for evening invasions. We also established that the fixed level of auroral absorption can be ensured if the electron flux in the summertime is higher than in the wintertime, which is accounted for by the known seasonal variations in parameters of the middle atmosphere and the lower ionosphere. Quantitative relationships are deduced between the absorption of cosmic radio waves and the total flux of precipitating high-energy electrons for morning and evening events of auroral absorption in different seasons.