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Ann. Geophys., 26, 131-143, 2008
www.ann-geophys.net/26/131/2008/
© European Geosciences Union 2008
The role of atomic oxygen concentration in the ionization balance of the lower ionosphere during solar proton events
A. Osepian1, V. Tereschenko1, P. Dalin2, and S. Kirkwood2
1Polar Geophysical Institute, Chalturuna 15, 183010 Murmansk, Russia
2Swedish Institute of Space Physics, P.O. Box 812, 98128 Kiruna, Sweden
Abstract. The influence of atomic oxygen concentration on the height distribution of
the main positive and negative ions and on electron density in the
mesosphere is studied for the conditions prevailing during the solar proton
event on 17 January 2005. It is shown by numerical modeling that the
electron and ion density profiles are strongly dependent on the choice of
the atomic oxygen profile. Experimental measurements of the electron density
are used as the criterion for choosing the atomic oxygen profile in the
mesosphere. With the help of modeling, the atomic oxygen profile in the
daytime in the winter mesosphere is found to lead to a model electron
density profile best matching the electron density profile obtained
experimentally. As a result, with the help of modeling, we find the atomic
oxygen profiles at various solar zenith angles in the winter mesosphere
which lead to model electron density profiles matching the electron density
profiles obtained experimentally.
Alteration of the atomic oxygen concentration leads to a redistribution of
the abundance of both positive and negative ion constituents, with changes
in their total concentrations and transition heights. In consequence this
results in changes of the electron density and effective recombination
coefficient. For conditions of low concentration of atomic oxygen (during a
solar proton event), the formation of cluster ions is the key process
determining electron and ion densities at altitudes up to 77 km. The complex
negative CO3− ion is formed up to about 74 km and the final
NO3− ion, which is stable in relation to the atomic oxygen, is the
dominant negative ion up to 74 km. As a result the transition heights
between cluster ions and molecular ions and between negative ions and
electron density are located at 77 km and 66 km, respectively.
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