Date of Award

Spring 2023

Project Type

Dissertation

Program or Major

Physics

Degree Name

Doctor of Philosophy

First Advisor

Christoforos Mouikis

Second Advisor

Roy Torbert

Third Advisor

Lynn Kistler

Abstract

Although the magnetotail plasma sheet predominantly consists of protons and electrons, singly charged oxygen ions, of ionospheric origin, are the third most abundant species in the plasma sheet. During disturbed times, the amount of oxygen ions in the plasma sheet and the inner magnetosphere can be comparable to the levels of the H+ ions and because of its larger mass, such a population of O+ in the near Earth magnetotail has the potential to modify the plasma sheet dynamics. It can affect the current sheet stability enhancing the growth rate of the ion tearing instability (ion scales) or alter overall the conditions surrounding the current sheet during the growth and expansion phases (meso and global scales). Close to the reconnection X-line, the behavior of the oxygen ions is different from the protons, due to the much larger gyroradius, which introduces an additional scale that results in a nested three scale diffusion region. Observations have shown that in the presence of more oxygen compared to protons, the substorm triggers at a higher total tail pressure, and then for the same events the tail unloading rate becomes faster (global scales). These effects of O+ ions on the substorm development, could indicate a faster reconnection rate in the presence of high O+ abundance (local micro-scales), or a wider reconnection site in the cross-tail direction GSM-Y (meso-scales), or totally different dynamics of the whole system during the events with higher oxygen ion density (global-scales). Using Cluster and MMS data, we investigated how the local reconnection rate is affected in events with a higher ratio of O+ to H+. Our results show that in contrast to the theoretical expectation that the reconnection rate decreases in the presence of higher total mass, there is a positive correlation between the magnetic reconnection rate and the number density ratio of O+ to H+. We conclude that this indicates that in the presence of high abundance of oxygen ions, the dynamics of the system at all scales are different and they overpower the effects of O+ in the reconnection micro-scales

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