Browsing by Subject "Aurora"

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    Preliminary bedrock geologic map of the Aurora quadrangle, St. Louis County, Minnesota
    (Minnesota Geological Survey, 1998) Morey, G.B.
    Preliminary bedrock geologic map of the Aurora quadrangle, scale 1:24,000
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    The storm time evolution in the night side high altitude field aligned wave Poynting flux and its relation to low altitude downward electron kinetic energy flux at low latitudes
    (2014-04) Thaller, Scott Alan
    In this thesis we investigate the evolution of the wave and large scale Poynting flux on earth's night side at altitudes from the auroral acceleration regions to the near earth tail over the course of major geomagnetic storms. Specifically, we are examining the field aligned components of the Poynting flux which carries energy from the tail into the auroral acceleration regions and to the ionosphere, and the down going field aligned electron kinetic energy flux. During major storm Poynting flux, over the range of observed time scales (from 6-180 seconds, and 600 -7200 seconds) intensify significantly (between one and three orders of magnitude), even down to low latitudes (≤ 65o invariant latitude). Concurrently, over the same range of latitudes, but at low altitudes, the downward electron kinetic energy flux enhances by at least an order of magnitude. The wave Poynting flux is thus shown to be a significant energy transport mechanism at low latitudes during storms, which provides strong evidence that Alfvén waves can be an important mechanism for auroral electron acceleration at low latitudes. This result is important, in part because low latitudes are on field lines mapping to the inner magnetosphere, and the nature of the energy transport processes associated with the near tail and inner magnetosphere are not yet fully understood. Most previous research on the Alfvén wave powered aurora focused on the higher latitude regions of the auroral zone and plasma sheet boundary layer. Prior studies were also conducted with either localized spacecraft conjunctions or with long term statistical compilations. The study presented herein is the first to examine the wave Poynting flux evolution over the course of major storms, from pre-storm, main phase, and recovery phase, from a high altitude standpoint on an orbit by orbit basis and to compare this to the low altitude electron kinetic energy flux. We find that the latitudinal evolution of the intensities of the high altitude wave Poynting flux and low altitude electron kinetic energy flux correspond well with each other. This suggests that there is a generative relation between them that exists over the course of the storm; i.e. either some of the electrons are accelerated by the waves or the electrons and waves are both produced by some third mechanism. A quantitative comparisons of the mapped wave Poynting flux to auroral images and to integrated electron kinetic energy flux, suggests the Poynting flux carries anywhere from ~5% to well over 100% of the energy needed to drive the low altitude electron acceleration processes. This fraction depends on both the level of geomagnetic activity and the assumptions that underlie the integration technique. The similarities between the distribution in time and latitude of the Poynting flux and electron kinetic energy flux extends to low latitudes (≤ 65o ILAT) during major storms. At such times the Poynting flux typically intensify about three orders of magnitude, to intensities of 1 to 10 ergs/cm2s, with such enhancements extending down to latitudes of at least 55o ILAT. The low latitude (≤ 65o ILAT), low altitude electron kinetic energy flux (peak intensities) are typically on the order of 0.1 ergs/cm2s pre storm, and intensifies to the order of 1 to 10s ergs/cm2s during storms. The existence of intense Poynting flux at low latitudes, similar to those at which intense downward electrons are also observed, suggest that Alfvén waves are important for, or at least closely related to, low latitude auroral acceleration processes. We also find that though the intense wave Poynting flux tends to occur in conjunction with large scale Poynting flux. And that while the wave Poynting flux is typically an order of magnitude greater in peak intensities, the large scale Poynting flux carries more energy to the ionosphere overall. The arrangement of this thesis is as follows. First, in the introduction, we go over basic space plasma physics with specific focus on energy transfer. We also discuss magnetohydrodynamics (MHD), Alfvén waves, and how Alfvén waves accelerate auroral electrons. In the second chapter we discuss previous work, both observational and theoretical, on the nature of Alfvén wave powered aurora. In the third chapter, we discuss the satellites, the instruments they carry, and other sources of data used in the research presented herein. In chapter four we present the main part of the thesis research, described above in this abstract. In the fifth chapter, we investigate the large scale Poynting flux and its relation to the wave Poynting flux. Finally, in chapter six, the conclusion, we summarize the findings.