Modeling the Response of the Middle Atmosphere to the October 1989 Solar Proton Event Using a Detailed Ion and Neutral Chemistry Model

Pekka Verronen1, Esa Turunen2, Thomas Ulich3, 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
3Dept. of Physical Sciences, P.O. Box 3000, FIN-90014 University of Oulu, Oulu, Finland.


Solar proton events and electron precipitation affect the chemical balance of the middle atmosphere. Ionization caused by precipitating particles leads to enhanced production of some chemically important minor neutral constituents, such as NO and OH. In special circumstances, these minor constituents affect the global ozone budget. Ionic reactions play an important role in minor neutral production. Therefore, when calculating effects of particle precipitation on the atmosphere and ionosphere, one has to take into account the reactions that couple the ionic and neutral constituents.

Finnish Meteorological Institute and Sodankylä Geophysical Observatory have developed a detailed ion and neutral chemistry model of the middle atmosphere that can be used to investigate the effect of particle events on several minor constituents, including ozone. Our new model is called STINCS, which is short form of Sodankylä Time-dependent Ion and Neutral Chemistry Solver, and it is based on the Sodankylä Ion Chemistry model. The time-dependency of our model allows detailed variations of ion and minor constituents' concentration to be followed, so that response to impulsive features in the observed proton precipitation as well as sunrise/sunset effects can be studied. At the moment STINCS includes over 300 chemical reactions and can be used to model the behaviour of 56 ion species and 9 neutral species. The altitude range of STINCS is 50 - 100 km.

We have used our model to study the effects of the October 1989 solar proton event on the middle atmospheric composition. Our results show that increase in ionization due to precipitating protons leads to large increases in electron and NO concentrations. Subsequent loss of ozone can is seen during night times, when solar radiation is absent, with maximum loss of 50% at 77 km during the most intense proton precipitation. A comparison with EISCAT incoherent scatter radar electron density measurements shows a good agreement between 60 and 90 km. However, there are up to 90% differences at other altitudes.