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

Modelling the ionospheric effects of solar proton events using the Sodankylä Ion Chemsitry model

M. A. Clilverd1, A. Seppälä2, C. J. Rodger3, N. R. Thomson3, P. T. Verronen2, E. Turunen4, Th.Ulich4, J. Lichtenberger5, P. Steinbach5

1British Antarctic Survey (NERC), Cambridge, U.K.,
2Finnish Meteorological Institute, Helsinki, Finland,
3Dept. of Physics, University of Otago, Dunedin, New Zealand,
4Sodankylä Geophysical Observatory, Sodankylä, Finland,
5Space Research Group, Eötvös University, Budapest, Hungary.


At Ny Ålesund, Svalbard, (78°54'N, 11°53'E, L~18) a narrow-band VLF receiver was used to monitor the behaviour of the phase and amplitude of several high power transmitters located in the Northern hemisphere under the influence of the solar proton events (SPE) of October/November 2003. We have used Sodankylä Ion Chemistry (SIC) atmospheric model profiles calculated at a single location in the northern winter-time polar region to investigate the radio propagation properties of several high latitude paths. Different paths showed different responses to the proton precipitation, but propagation modelling was able to account for all of these types of behaviour. The same SIC profiles were able to model the SPE response on partial polar cap paths by being applied to only part of the path, leaving normal ionospheric conditions on the remainder of the path. Using the SIC-based electron density profiles we have been able to develop models of ionospheric effective height (h') and sharpness (b) in order to describe the D-region behavour during SPEs. As a result, our understanding of VLF propagation influenced by SPEs is high, such that VLF observations might be used to predict changes in the ionospheric D-region electron density profiles during other particle precipitation events.