Spectral studies of small-scale auroral structure and plasma instability in the high-latitude ionosphere

Optical measurements of small-scale auroral structures are here combined with spectrographic data in order to study the relationship between auroral morphology and the energy characteristics of the precipitating population. It is shown that rayed auroral structures are associated with precipitating...

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Main Author: Sullivan, Joanna Mary
Format: Thesis
Language:English
Published: 2008
Subjects:
Online Access:https://eprints.soton.ac.uk/65694/
https://eprints.soton.ac.uk/65694/1/JSullivan_thesis.pdf
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spelling ftsouthampton:oai:eprints.soton.ac.uk:65694 2023-07-30T04:03:16+02:00 Spectral studies of small-scale auroral structure and plasma instability in the high-latitude ionosphere Sullivan, Joanna Mary 2008-11 text https://eprints.soton.ac.uk/65694/ https://eprints.soton.ac.uk/65694/1/JSullivan_thesis.pdf en eng https://eprints.soton.ac.uk/65694/1/JSullivan_thesis.pdf Sullivan, Joanna Mary (2008) Spectral studies of small-scale auroral structure and plasma instability in the high-latitude ionosphere. University of Southampton, School of Physics and Astronomy, Doctoral Thesis, 189pp. Thesis NonPeerReviewed 2008 ftsouthampton 2023-07-09T21:04:53Z Optical measurements of small-scale auroral structures are here combined with spectrographic data in order to study the relationship between auroral morphology and the energy characteristics of the precipitating population. It is shown that rayed auroral structures are associated with precipitating electrons with a broad range in energy, including a significant population at energies of around 100 eV. In comparison, observations of fast-moving auroral arc elements are shown to result from precipitation energy distributions peaking at several keV with a very small low-energy component. This spectrographic information feeds directly into the study of naturally enhanced ion-acoustic lines, or NEIALs, which have been observed by incoherent-scatter radars at high-latitudes. It has been proposed that these radar enhancements result from natural plasma instability, causing the generation of ion-acoustic waves through the decay of unstable Langmuir waves, themselves driven by low-energy electron streams. Using multi-spectral imaging in combination with radar observations, a direct link is shown between ion-acoustic wave enhancements and precipitating electrons at 100 eV energies. Wave enhancements at the radar wavevector which are three orders of magnitude above the thermal level, are successfully modelled using the Langmuir decay interpretation for the time of observation. Electron populations with a broad energy range are thought to result from Alfv´enic acceleration mechanisms, which play an important role in the generation of smallscale auroral structure. With the recent advancements in multi-spectral imaging, it is now possible to resolve auroral filaments of a few hundred meters width. An interferometric imaging capability is under development for the EISCAT Svalbard Radar system, in order to resolve scattering wave structures on similar spatial scales within the radar beam. A technique is demonstrated by which to calibrate the position of coherent echoes detected by the interferometer. This will be of great use ... Thesis EISCAT Svalbard University of Southampton: e-Prints Soton Svalbard Langmuir ENVELOPE(-67.150,-67.150,-66.967,-66.967)
institution Open Polar
collection University of Southampton: e-Prints Soton
op_collection_id ftsouthampton
language English
description Optical measurements of small-scale auroral structures are here combined with spectrographic data in order to study the relationship between auroral morphology and the energy characteristics of the precipitating population. It is shown that rayed auroral structures are associated with precipitating electrons with a broad range in energy, including a significant population at energies of around 100 eV. In comparison, observations of fast-moving auroral arc elements are shown to result from precipitation energy distributions peaking at several keV with a very small low-energy component. This spectrographic information feeds directly into the study of naturally enhanced ion-acoustic lines, or NEIALs, which have been observed by incoherent-scatter radars at high-latitudes. It has been proposed that these radar enhancements result from natural plasma instability, causing the generation of ion-acoustic waves through the decay of unstable Langmuir waves, themselves driven by low-energy electron streams. Using multi-spectral imaging in combination with radar observations, a direct link is shown between ion-acoustic wave enhancements and precipitating electrons at 100 eV energies. Wave enhancements at the radar wavevector which are three orders of magnitude above the thermal level, are successfully modelled using the Langmuir decay interpretation for the time of observation. Electron populations with a broad energy range are thought to result from Alfv´enic acceleration mechanisms, which play an important role in the generation of smallscale auroral structure. With the recent advancements in multi-spectral imaging, it is now possible to resolve auroral filaments of a few hundred meters width. An interferometric imaging capability is under development for the EISCAT Svalbard Radar system, in order to resolve scattering wave structures on similar spatial scales within the radar beam. A technique is demonstrated by which to calibrate the position of coherent echoes detected by the interferometer. This will be of great use ...
format Thesis
author Sullivan, Joanna Mary
spellingShingle Sullivan, Joanna Mary
Spectral studies of small-scale auroral structure and plasma instability in the high-latitude ionosphere
author_facet Sullivan, Joanna Mary
author_sort Sullivan, Joanna Mary
title Spectral studies of small-scale auroral structure and plasma instability in the high-latitude ionosphere
title_short Spectral studies of small-scale auroral structure and plasma instability in the high-latitude ionosphere
title_full Spectral studies of small-scale auroral structure and plasma instability in the high-latitude ionosphere
title_fullStr Spectral studies of small-scale auroral structure and plasma instability in the high-latitude ionosphere
title_full_unstemmed Spectral studies of small-scale auroral structure and plasma instability in the high-latitude ionosphere
title_sort spectral studies of small-scale auroral structure and plasma instability in the high-latitude ionosphere
publishDate 2008
url https://eprints.soton.ac.uk/65694/
https://eprints.soton.ac.uk/65694/1/JSullivan_thesis.pdf
long_lat ENVELOPE(-67.150,-67.150,-66.967,-66.967)
geographic Svalbard
Langmuir
geographic_facet Svalbard
Langmuir
genre EISCAT
Svalbard
genre_facet EISCAT
Svalbard
op_relation https://eprints.soton.ac.uk/65694/1/JSullivan_thesis.pdf
Sullivan, Joanna Mary (2008) Spectral studies of small-scale auroral structure and plasma instability in the high-latitude ionosphere. University of Southampton, School of Physics and Astronomy, Doctoral Thesis, 189pp.
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