4th IAGA/ICMA/CAWSES Workshop on Long-Term Changes and Trends in the Atmosphere, Sodankylš, Finland, 4-8 September 2006

The effect of variable solar short-wave radiation on the concentration of nitric oxide in the MLT region

C.-F. Enell1, E. Turunen1, T. Turunen1, Th.Ulich1, A. Seppälä2, P. T. Verronen2

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


A current important issue in the understanding of the mesosphere-lower thermosphere (MLT) region is that most models underestimate the observed concentrations of nitric oxide (NO).

We therefore propose to study the effect of the highly variable solar extreme UV (EUV) and X-ray irradiances on the concentration of nitric oxide in the MLT region by interpreting the accurate electron density measurements made possible by a modern research ionosonde, the new Sodankylä Alpha Wolf (SAW). SAW is a fully digital continuous-wave chirp sounder which is much more sensitive than our previous ionosonde - hence it makes accurate electron density monitoring possible both for extremely quiet and moderately disturbed conditions.

We here compare SAW measurements for selected events in the winter of 2005-2006 with results from our 1-dimensional, coupled ion and neutral chemistry model SIC (Sodankylä Ion Chemistry), run with EUV and X-ray input data available from e.g. the TIMED and GOES satellites.