Modeling Mesospheric Odd Nitrogen During the October 1989 SPE with the detailed Sodankylä Ion-Neutral Chemistry Model

Pekka Verronen1, Esa Turunen2, Thomas Ulich2, and Erkki Kyrölä1

1Finnish Meteorological Institute, Geophysical Research, P.O. Box 503, FIN-00101 Helsinki, Finland
2Sodankylä Geophysical Observatory, Tähteläntie 112, FIN-99600 Sodankylä, Finland


Precipitation of energetic particles affects the chemical balance of the middle atmosphere. It leads to enhanced production of some important minor neutral constituents, such as NO and OH, which might affect the ozone budget. Ion-neutral reactions play an important role in the production of minor neutrals. The Sodankylä Ion Chemistry (SIC) model was revised by combining relevant neutral chemistry with ion chemistry and is now used to investigate the effect of precipitation events on minor constituents, including NO and ozone. The new model covers altitudes from 50 to 100 km and can be used as steady-state or time-dependent model. At the moment SIC includes over 400 chemical reactions and models the behavior of 55 ion and 9 neutral species. The time-dependent model allows short-term variations of these species to be followed, so that their response to observed precipitation events or to sunrise/sunset effects can be studied in detail. We have modeled the behavior of odd nitrogen above Tromsø (69.59°N 19.23°E) during the October 1989 solar proton event. Our results show how the intense particle ionization significantly increases the amount of atomic nitrogen and affects the N(4S)/N(2D) balance through ionic reactions. Also, ionic sources become important in NO production. As a consequence, NO is greatly enhanced between 60 and 100 km during days and between 50 and 100 km during nights. The increase of NO, up to three orders of magnitude, lasts beyond the end of the SPE. Ozone decrease due to reactions with enhanced odd nitrogen, odd hydrogen, and negative ions is seen below 85 km during nights, when sunlight is not present. Our modeling results for the sunset on the 23rd of October are compared with EISCAT incoherent scatter radar electron density measurements and a good agreement is found between 55 and 90 km.