Radar observations of convection in the nightside high-latitude ionosphere

The work discussed in this thesis concerns the ionospheric flow response to different magnetospheric phenomena which occur under various interplanetary and geomagnetic conditions. This was undertaken primarily using the SuperDARN HF radar network located in the auroral regions of both hemispheres, but also utilised magnetometer and spacecraft data from a variety of sources. A detailed case study is first presented concerning the nature of convection in the nightside ionospheric during an isolated substorm. The results of this study unequivocally demonstrate that twin-vortex flow can be excited in association with substorm expansion, a phenomenon which has previously been the subject of some controversy. Two further case studies are presented of the ionospheric flows which exist during intervals of northward, but (negative) By-dominated IMF. Under these conditions it is found that the substorm cycle dies away, but that Dungey-cycle flow persists for many hours. During these intervals, strong 'bursts' of flow were observed in the nightside ionosphere, which are found to be associated with episodic reconnection in the distant magnetic tail. This study has shed new light on the magnetospheric response to an IMF of intermediate clock angles, revealing that the Dungey-cycle and the substorm cycle are not, in fact, synonymous. Finally, a discussion of ongoing and possible future work is given, which is suggested by the results of the studies described above, with initial results from a number of pilot studies being presented. The flows during a number of substorm events have been studied, which reveal that the excitation of flow appears to accompany substorm expansions in general. Also, a study of the flows during another interval of northward IMF now dominated by positive By provides an appropriate counterpart to the negative By case. This preliminary investigation reveals flows of a similar nature but with the expected opposite sense of By-asymmetry.