VLF wave propagation and middle polar atmosphere as a detector of ultra-energetic relativistic electron precipitations in 1988–1992 years

Abstract

In this paper we present a catalog of the new geophysical phenomena, Ultra-energetic Relativistic Electron Precipitations (UREP), and relying on our previous physics analysis of it, describe its specific quantitative characteristics. This full dataset was created based on the continuous very low frequency measurements of a polar radio path with three working frequencies during the years 1988–1992. As discussed in our previous works, the main feature of this phenomenon is that ultra-energetic relativistic electrons precipitate into the middle polar atmosphere and cause additional ionization at the altitudes 10–45 km by the bremsstrahlung X-rays and gamma rays which are generated by the ~100 MeV penetrating electrons. This new geophysical phenomenon was detected by the ground-based measurements of the Very Low Frequency (VLF) signal variations due to the signals' passing along the terrestrial waveguide with a sporadic layer of ionization created by the X-ray radiation in the middle atmosphere. Therefore, in all these abnormal cases the middle atmosphere and the processes of VLF wave propagation are the detector of this new effect.In the dataset presented, each event is identified by the abnormal values of VLF signals variations which are not typical for the measurements in the distance zone of measurements. In a case of this moderate distance from a VLF ground based source (~900 km), which is investigated here, the abnormality manifests in the qualitatively similar negative type of variations in both phase and amplitude of the detected signals for all 3 used radio wave frequencies. Such similarity appears due to the signal of strait seeing turns into the diffraction wave, the 1-st hop (ray) becomes ~ 2 times less. The indicated abnormality in the experimental variations proves that the second sky wave does not reach a receiver and there is an anti-phase interference effect between two field terms at the middle distance zone, previously unknown. Over 1988–1992 years, 135 VLF disturbances have been observed (with 17 events during the night) with mentioned abnormal behavior: 7 powerful disturbances, 72 strong disturbances and 56 moderate disturbances. It is known that the corresponding minimal values of effective height (altitude) of these VLF disturbances are: 25–35 km for powerful, 35–45 km for strong, and 45–55 km for moderate disturbances.