IAGA 2005 Scientific Assembly, Toulouse, France, 18-29 July 2005

The high energy proton fluxes of January 2005: Impact on middle atmosphere

A. Seppälä1, M. A. Clilverd2, C. J. Rodger3, E. Turunen4, Th. Ulich4, C.-F. Enell4

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


On January 20th, 2005, the giant sunspot 720 produced a powerful X-class solar flare. From this flare began an extraordinary solar proton storm: the flux of the solar protons with the highest energies (>100 MeV) was of the same order as in the well known October 1989 Solar Proton Event (SPE), whilst the lower energy fluxes remained at moderate levels, making the January event the hardest and most energetic proton event of Cycle 23 so far.

The solar protons with very high energies are able to cause ionization in the polar atmosphere down to middle - lower stratosphere (100 MeV protons can reach the altitude of 30 km). As a result ion chemistry leads to increased production of odd nitrogen (NOx) and odd hydrogen (HOx) in this atmospheric area. These gases participate in catalytic reaction cycles that decrease the amount of ozone in middle atmosphere.

We have used the Sodankylä Ion Chemistry model (SIC) and Very Low Frequency (VLF) subionospheric propagation observations and modelling to study the conditions in the northern and southern polar atmospheres during the January events. The SIC model can be used to predict the response of the NOx, and HOx constituents to the precipitating high proton fluxes, and the subsequent effect of NOx, and HOx on ozone. This model also produces the ionospheric D-region electron densities which can further be used as an input to a VLF subionospheric propagation modelling for comparison with experimental observations.

In this presentation we will show the results from the SIC modelling for the January 2005 solar proton storm series, contrasting the effects of different levels of proton spectral hardness.