Date of Award

Winter 2011

Project Type

Dissertation

Program or Major

Physics

Degree Name

Doctor of Philosophy

First Advisor

Lynn M Kistler

Abstract

Using Cluster/CODIF data, we have determined the occurrence frequency of the cusp-source O+ in the magnetotail to determine where and when it is observed. The results show that the probability to observe O+ along the transport path is high even during nonstorm times, although, as expected, the highest probability is found during storm times. In addition to the outflow rate increasing, the transport path itself also changes during storm times, bringing more O+ to the near-earth plasma sheet. Interplanetary magnetic field (IMF) magnitude is the most effective driver for bringing O+ into the near-Earth lobes. It was also found that when IMF By is positive, O+ from the northern cusp/cleft tends to stream towards the dawnside while O+ from the south is observed on the duskside. The transport path for negative IMF By is more symmetric, but shows some evidence for a reversed asymmetry when IMF By is strongly negative. The asymmetry most likely results from the combination of the convection driven by the solar wind and the coupling with the ionosphere. By comparing the normalized distributions of the cusp outflow and the streaming O+ in the magnetotail we show that the increase in the energy of the streaming O+ in the tail lobes is mainly due to the velocity filter effect, not due to acceleration. O+ entering from the lobe into the plasma sheet boundary layer, however, has been accelerated. A case study shows that most of the velocity increase is due to E x B drift, but additional acceleration along the electric field is also found. The probability to observe streaming O + decreases steeply during the declining phase of solar cycle 23 and increases again at the start of solar cycle 24. The reduction factor is much larger in the tail lobes than in the polar cap, due to a change in the transport path.

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