Radar observations of energy deposition and dissipation in the high-latitude ionosphere.

The high-latitude ionosphere is a dynamic region, in which a variety of phenomena including particle precipitation, currents and waves contribute to the energy budget. In this thesis, statistical and case studies of ion frictional heating are presented, including investigations into the dependence of enhanced ion temperature on time and altitude. The relationship between parallel ion temperature and ion velocity is compared to simplified forms of the ion energy balance equation. In addition, the generation mechanisms of atmospheric gravity waves are studied by means of measurements made during the WAGS campaign of October 1985. The results indicate that auroral precipitation can influence frictional heating events to a greater extent than has previously been realised and that during frictional heating the molecular content of the lower ionosphere is enhanced, affecting the electron density. Any analysis which takes no account of the modified composition underestimates the parallel ion temperature, particularly between 200 and 300 km altitude. The relationship between ion velocity and parallel ion temperature is most easily explained by an anisotropic ion velocity distribution, consistent with resonant charge exchange collisions. The relationship varies with altitude, however, possibly due to ion-ion collisions. An experimental method is described by which the temperature anisotropy can be obtained directly and early results are discussed. For the investigation of atmospheric gravity waves and their sources, HF Doppler observations in the UK enabled wave speeds and azimuths to be deduced, whilst EISCAT simultaneously observed the possible source region. Although the study was characterised by moderate activity, more active days showed higher phase speeds and southerly azimuths. Some of these waves may have originated at high latitudes during positive bay activity, when both Joule heating and the Lorentz force contributed to wave generation.