Ion frictional heating in the high-latitude ionosphere.

At auroral latitudes, large electric fields drive the F-region plasma of the ionosphere through the thermosphere, heating the ion population through frictional contact with the neutral gas. Ion frictional heating, which can double the unperturbed ion temperature, is an important manifestation of both magnetosphere-ionosphere and ionosphere-thermosphere interaction and provides a significant contribution to the energy budget of the ionosphere and neutral atmosphere at high-latitudes. Perhaps the single most powerful technique for ground based remote sensing of the ionosphere is incoherent scatter. The EISCAT radar facility, located in northern Scandinavia, employs this technique to investigate the highly dynamic nature of the high-latitude ionosphere. This thesis documents a study of ion frictional heating in the high-latitude ionosphere, principally employing common programme observations by the tristatic EISCAT UHF system. In excess of 3200 hours of EISCAT observations, taken during a six year period, were employed to study, on a statistical basis, ion frictional heating in the high-latitude F-region. The diurnal distribution of frictional heating was established and its dependence on such factors as geomagnetic activity and solar cycle was investigated; the distributions were interpreted with reference to corresponding distributions of enhanced ion velocity. A prolonged and intense interval of ion frictional heating was observed by EISCAT postnoon on 04/03/1992: this interval was modelled, using the Sheffield University plasmasphere and ionosphere model, and the model results compared with the observations. This study highlights the importance of ionospheric effects in determining neutral dynamics, particularly on the dayside. Furthermore, during this interval, the altitude dependence of the effect of enhanced electric fields on the velocity and temperature of the ion population was studied and, moreover, employed to provide first-order estimates of the normalised ion-neutral collision frequency and the neutral wind at E-region altitudes.