Ionospheric Convection and Auroral Responses to Solar Wind Driving

Walach, Maria-Theresia and Milan, S.E. and Yeoman, T.K. (2017) Ionospheric Convection and Auroral Responses to Solar Wind Driving. PhD thesis, Univ Leicester, University of Leicester.

Abstract

This thesis studies the large-scale dynamics in the Earth's magnetosphere due to solar wind driving. When the interplanetary magnetic field (IMF) is orientated southward, reconnection on the dayside magnetopause opens magnetic flux, which eventually reconnects in the magnetotail. When dayside reconnection is dominant, the polar cap, the area where open magnetic flux meets the Earth's surface, increases. Similarly, when nightside reconnection is dominant, the polar cap decreases in size. This framework is known as the expanding and contracting polar cap paradigm (ECPC). Part of this thesis considers the ionospheric flows, a part of the ECPC, which relates global auroral imagery of the size of the polar cap through a physics-based model of the ECPC, and compares the calculated ionospheric flow velocities to satellite, and ground-based measurements of plasma drift. The comparison also discusses the known limitations of the model and the observations. In the following chapters, specific events within the ECPC, or magnetospheric modes, are put into the context of solar wind driving and the auroral response. Substorms are a sporadic magnetospheric response mode, where the polar cap expands at first, followed by a distinct nightside brightening of the aurora and a decrease in polar cap flux. Steady magnetospheric convection events (SMCs) are times when the day and nightside reconnection rates are balanced, such that the polar cap flux stays constant. By considering dayside reconnection rates and the magnetospheric response during these events, it is established that the majority of SMCs are part of the substorm cycle. Sawtooth events (SEs) appear as a quasi-periodic version of substorms, but occur under more extreme solar wind driving. It is shown that the aurora behaves according to the ECPC in terms of latitudinal expansions and contractions, but the temporal behaviour is significantly different from substorms.