Electrodynamics of the auroral ionosphere during magnetospheric substorms

One of the principal consequences of magnetic reconnection at the dayside magentopause is the transfer of solar wind energy in the Earth's magnetotail. The expansion phase of a magnetospheric substorm corresponds to the sudden release of this energy and is characterised in the ionosphere by the sudden brightening and poleward expansion of the auroral oval near midnight and the intensification of the ionospheric currents flowing in the auroral zone. Observations of various high-latitude ionospheric phenomena associated with magnetospheric substorm are presented. In particular, use is made of the Co-operative UK Twin Located Auroral Sounding System (CUTLASS), a high frequency bistatic coherent-scatter radar with sites in Finland and Iceland.;Azimuthally Propagating Vortical Currents (APVCs) are the ionospheric flow signatures of upward directed field-aligned currents in the nightside ionosphere. Two case studies of APVCs are presented and their structure examined in detail. In addition, the results of a statistical study of APVC occurrence encompassing over 1000 hours of high-time resolution data are discussed with particular focus on the relationship of APVCs to magnetospheric substorm phase. Omega bands are a distinct class of auroral form that have previously been observed in the morning sector during the recovery phase of magnetospheric substorms. High-time resolution measurements of the ionospheric flow within a series of omega bands from the CUTLASS Finland radar are presented. Complementary observations from the Scandinavian Twin Auroral Radar Experiment (STARE) and ground magnetometers of the IMAGE array are employed in order to characterise the electric and magnetic field structure of omega bands. Revised descriptions of omega band structure and formation mechanism are proposed. Finally, multi-instrument observations of the evolution of a high-latitude polar auroral arc during the recovery phase of an isolated substorm are presented and its relation to upstream interplanetary magnetic field conditions discussed.