The interaction between the thermosphere and ionosphere at high latitudes

Abstract

A study has been made of the interaction between the thermosphere and the ionosphere at high latitudes, with particular attention to the value of the 0⁺-0 collision parameter. The European Incoherent SCATter facility (EISCAT) based at Troms0 was used to make tristatic measurements of plasma parameters at F region altitudes while simultaneous independent measurements of the neutral wind were made by a Fabry-Perot Interferometer (FPI). The radar data were used to derive values of the meridional neutral wind. The accuracy of this technique at high latitudes is reduced by the dynamic nature of the auroral ionosphere and the presence of significant vertical winds. The derived winds were compared with the meridional winds measured by the FPI. For each night, the value of the 0*-0 collision parameter was found which produced the best agreement between the two data sets.
The precision of the collision frequency obtained in this way depends on the accuracy of the data. The statistical method was critically examined in an attempt to account for the variability in the data sets. The results indicate that the most probable value of the 0⁺-0 collision parameter is a factor of between 1.2 and 1.7 greater than Banks' theoretical value (Banks, 1966).
The contribution of ion drag to the acceleration of the neutral air was also considered. During times of enhanced ion drift, ion drag dominates all other forces acting on the neutral air. A method for determining the neutral ioncollisi on frequency during such an event is described. It was not possible to calculate the neutral ion collision frequency for the two examples in this thesis due to limitations in the radar data.

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