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Ann. Geophys., 20, 1967-1976, 2002
www.ann-geophys.net/20/1967/2002/
© European Geosciences Union 2002
Modelling the effects of the October 1989 solar proton event on mesospheric odd nitrogen using a detailed ion and neutral chemistry model
P. T. Verronen1, E. Turunen2, Th. Ulich2, and E. Kyrölä1
1Finnish Meteorological Institute, Geophysical Research Division, P.O. Box 503, 00101 Helsinki, Finland
2Sodankylä Geophysical Observatory, Tähteläntie 112, 99600 Sodankylä, Finland
Correspondence to: P. T. Verronen (pekka.verronen@fmi.fi)
Abstract. Solar proton events and
electron precipitation affect the concentrations of middle atmospheric
constituents. Ionization caused by precipitating particles enhances the
production of important minor neutral constituents, such as nitric oxide,
through reaction chains in which ionic reactions play an important role. The
Sodankylä Ion Chemistry model (SIC) has been modified and extended into a
detailed ion and neutral chemistry model of the mesosphere. Our steady-state
model (containing 55 ion species, 8 neutral species, and several hundred
chemical reactions) is used to investigate the effect of the October 1989 solar
proton event on odd nitrogen at altitudes between 50–90 km. The modelling
results show that the NO concentration is significantly enhanced due to the
proton precipitation, reaching 107 –108 cm-3
throughout the mesosphere on the 20 October when the proton forcing was most
severe. A comparison between the chemical production channels of odd nitrogen
indicates that ion chemical reactions are an important factor in the total odd
nitrogen production during intense ionization. The modelled electron
concentration for the 23 October is compared with EISCAT incoherent scatter
radar measurements and a reasonable agreement is found.
Key words. Atmospheric composition
and structure (Middle atmosphere – composition and chemistry); Ionosphere
(Particle precipitation)
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