Energy characteristics of precipitating relativistic electrons as determined from EISCAT, VLF propagation and riometer data using D-region ion chemistry modelling

Turunen, E.1, Ulich, Th.1, Enell, C.-F.1, Kero, A.1, Raita, T.1, Manninen, J.1 and Verronen, P.2

1 Sodankylš Geophysical Observatory, Sodankylš, Finland
2 Finnish Meteorological Institute, Helsinki, Finland

The temporal variability of the relativistic electron population is reasonably well characterized with numerous satellite measurements. However, implications of the precipitation of the relativistic electrons (REP) into the atmosphere are not well known. A major deficiency is a missing global picture of the precipitation. The EISCAT radars can record the excess ionisation due to REP partly in the lower ionosphere, but supporting information from other ground -based measurements is needed for interpretation of the REP characteristics. One of the experimental techniques which can probe the atmosphere for the presence of REP uses the propagation of very low-frequency (VLF) electromagnetic radiation in the Earth-ionosphere waveguide. VLF signals can be recorded thousands of kilometres from their sources. The variability of the received signals is mostly due changes at and below the lower ionosphere. In this paper we show how the temporal features seen in the VLF signals, with necessary supporting information from EISCAT and riometer measurements, can be used to estimate the energy characteristics of the precipitating electrons, using detailed ion-chemistry modeling of the lower ionosphere.