Space and ground based studies of transpolar arcs

This thesis presents a study of the formation and dynamics of 6 transpolar arcs. This work was undertaken primarily using auroral emission data from the Imager Magnetopause-to-Aurora Global Exploration (IMAGE) spacecraft along with the ionospheric convection flow patterns from the Super Dual Auroral Radar Network HF radars located in the auroral regions of both hemispheres. Particle precipitation data from Defence Meteorological Satellite Program (DMSP) and National Oceanic and Atmosphere Administration (NOAA) satellites were also used, together with Field Aligned Current data from the Iridium satellite constellation. A detailed study is first presented concerning the nature of the ionospheric convection flows on the nightside during an isolated transpolar arc. The results of this study demonstrated: a) the occurrence of cross midnight azimuthal flows, which are thought to be associated with the formation of the transpolar arc; and b) that ionospheric flows caused by dayside reconnection were responsible for the motion of the transpolar arcs. Five further case studies of transpolar arcs, which exist during intervals of northward but different IMF By components, are also discussed. The flows during a number of transpolar arc events have been studied, which confirm that the excitation of flow appears to accompany transpolar arc dynamics in general. Also, a detailed study of particle precipitation data suggests that the particles associated with the transpolar arcs are located on closed field lines. Evidence presented in this thesis suggests that the transpolar arcs mentioned above lie on closed field lines. Finally, a discussion of possible future work is given, suggested by the results of the studies described above.