Observational and simulation studies of the structure of Earth’s magnetotail during periods of northward IMF

Abstract

This thesis investigates the effect that northward IMF (Interplanetary Magnetic Field) has on the Earth’s magnetotail using observational case studies and magnetospheric simulations. The relationship between the solar wind, the Earth’s magnetosphere and the ionosphere during northward IMF are not as readily studied as southward IMF; hence, there are many unanswered questions relating to northward IMF dynamics, some of which we aim to address within this thesis. The magnetotail regions have been sampled by a small number of spacecraft which provide local in-situ measurements during northward IMF. We detail the results of our observational study which look at three case studies when the Cluster spacecraft was located in the high latitude lobe regions and measured uncharacteristically ’hot’ plasma. We use in-situ particle data to compare the plasma characteristics to two proposed models which explain the presence of hot plasma populations located at high latitudes and find multiple consistencies between the plasma data and a closed field line topology. We show that in each of the three events, the plasma is likely located on a closed field line which forms as the result of magnetotail reconnection during northward IMF, and that these events also coincide with transpolar arc observations. Due to the good correspondence between the closed field line model and the observational case studies, we investigate how such a closed structure could form on a global scale during northward IMF. To do this, we present in Chapter 5 a re-examination of a previously-published global MHD (Magnetohydrodynamic) simulation during northward IMF. We find evidence of magnetotail reconnection within this simulation run, which forms a transpolar arc (interpreted from the formation of a large closed magnetotail structure). We build on this further in Chapter 6 by looking at how initialising the simulation with southward IMF affects the consistency with our previous simulation runs. Lastly, in Chapter 7, we investigate the relationship between solar wind pressure pulses and transpolar arc signatures in global simulations, which has not been previously explored in the literature.

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Identifiers

ORCID for Laura Jane Fryer: orcid.org/0000-0002-5215-6942

ORCID for Robert Fear: orcid.org/0000-0003-0589-7147

ORCID for Imogen Gingell: orcid.org/0000-0003-2218-1909

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