2nd VERSIM Workshop 2006, Sodankylä, Finland, 26-30 September 2006

What if we knew the energy characteristics of precipitating relativistic electrons using VLF recordings and D-region ion chemistry modelling?

E. Turunen1, C. J. Rodger2, P. T. Verronen3, A. Seppälä3, Th.Ulich1, M. A. Clilverd4, K. Kaila5, C.-F. Enell1, T. Raita1, J. Manninen1, T. Turunen1

1Sodankylä Geophysical Observatory, Sodankylä, Finland,
2Dept. of Physics, University of Otago, Dunedin, New Zealand,
3Finnish Meteorological Institute, Helsinki, Finland,
4British Antarctic Survey (NERC), Cambridge, U.K.,
5Dept of Physical Sciences, University of Oulu, Oulu, Finland


Satellite measurements on radiation belt electrons are numerous and the temporal variability of the relativistic electron population is reasonably well characterized. However, actual atmospheric implications of the precipitation of the relativistic electrons are not well known. A major deficiency is missing global picture from atmospheric measurements. One of the experimental techniques, which can probe the relevant altitudes, uses the propagation of very low-frequency (VLF) electromagnetic radiation in the Earthionosphere 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. Systems such as the Antarctic-Arctic Radiation-belt (Dynamic) Deposition - VLF Atmospheric Research Konsortium (AARDDVARK) should prove to be very useful tools in global, continuous monitoring of the lower ionosphere.

Model estimates of possible neutral composition and chemistry effects due to excess ionisation by the precipitating relativistic electrons need information on temporal and spatial variations of the energy and flux of the electrons. In this paper we show how temporal features seen in the VLF signals, with assumptions, can be used to estimate the energy characteristics of the precipitating electrons, using detailed ion-chemistry modelling of the lower ionosphere.