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Multi-instrument studies of ionospheric and magnetospheric processes



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In this thesis, several aspects of the convection, magnetic, and optical auroral dynamics of the high-latitude ionosphere are investigated from multi-instrument observations. The spatial and temporal relationships between nightside radar flow enhancements (NRFEs) and auroral intensifications are studied in Chapter 3. The NRFEs on open field lines usually are associated with very little accompanying auroral and magnetic activity. The NRFEs on closed field lines are often accompanied by optical auroral activity, but there is not a definite one-to-one correspondence. Both the statistical investigation and event study showed that the NRFEs may occur nearly simultaneously with the auroral intensifications. Because existing models associating the tail reconnection process and near-geosynchronous onset of substorms do not explain these correlated radar and optical observations very well, we propose a new model to explain the nearly simultaneous onset of the NRFEs and the auroral intensifications. In Chapter 4 we describe a small postmidnight substorm event on October 9, 2000 during dominantly IMF By+ Bz+ conditions. A sequence of three optical auroral intensifications and Pi2 bursts were found. The first two activations were characteristic of pseudobreakups, while the last and strongest intensification corresponded to a substorm expansive phase (EP). The auroral, magnetic and radar signatures of the event are interpreted as the consequence of three successive drift-Alfven-ballooning (DAB) mode instabilities in the near-geosynchronous orbit plasma sheet (NGOPS). About 10 minutes after the EP onset, there was a second auroral brightening. The convection feature during this second auroral brightening was consistent with the scenario of a Stage-2 EP. We suggest that the first two pseudobreakups, the Stage-1 EP, and the Stage-2 EP are related, respectively, to loading-unloading, directly driven, and internal magnetotail processes. Finally, in Chapter 5, we make some comparisons between the ionospheric plasma convection vortex structure observed by SuperDARN and the associated equivalent current pattern derived from the magnetometer observations. The discrepancies between the equivalent convection (EQC) and the SuperDARN-observed convection (SDC) pattern are explained in terms of the effect of day-night photoionization conductance gradient, and the coupling between field-aligned currents (FACs) and ionospheric conductances. In particular, we found the agreement between the EQC and SDC patterns is rather poor for a counterclockwise convection vortex. We suggest the discrepancies are probably due to a downward FAC-conductance coupling process.



plasma convection, magnetospheirc physics, Ionospheric physics, aurora, Substorm



Doctor of Philosophy (Ph.D.)


Physics and Engineering Physics


Physics and Engineering Physics


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