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

Importance of Proton Spectral Hardness in the Atmospheric Effects of Solar Proton Events - the Jan 2005 Events

A. Seppälä1, P. T. Verronen1, M. A. Clilverd2, C. J. Rodger3, E. Turunen4, Th.Ulich4, C.-F. Enell4, V. F. Sofieva1, J. Tamminen1, E. Kyrölä1

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


On January 20, 2005, the giant sunspot 720 produced a powerful X-class solar flare. From this flare began an extraordinary solar proton storm: the flux with the highest energies was of the same order as in the well known October 1989 SPE, whilst the lower energy fluxes remained at moderate levels, making this event the hardest and most energetic proton event of Cycle 23 so far. The high energy protons ionize the polar atmosphere and following ion chemistry leads to increased production of NOx and HOx which, in turn, participate in catalytic, ozone destroying reaction cycles.

We have used the SIC model and VLF subionospheric propagation observations and modeling as well as atmospheric measurements by the GOMOS instrument to study the conditions in the polar atmosphere during the January events. The SIC model was used to predict the response of the NOx, and HOx constituents to the high proton fluxes, and the subsequent effect on ozone. SIC also produces the ionospheric D-region electron densities which are further used as an input to a VLF subionospheric propagation modeling for comparison with experimental observations. We will present these results from the January 2005 solar proton storms, contrasting the effects of different levels of proton spectral hardness.