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Fine-scale morphology and spectral characteristics of active aurora
KTH, School of Electrical Engineering (EES), Space and Plasma Physics.ORCID iD: 0000-0001-5596-346X
2008 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

Ground-based and in-situ observations of the aurora demonstrate an extreme richness in fine structure, with spatial scales down to tens of metres and time variations occurring on a fraction of a second. To further our understanding of the aurora, it is esssential to understand the mechanisms responsible for the small-scale structuring, since this is an intrinsic property of the auroral plasma. Still many questions about dynamics and structuring of aurora on small scales remain unanswered. In this thesis the low-light optical instrument ASK (Auroral Structure and Kinetics) is used to image small-scale structures in the aurora at very high spatial and temporal resolution. ASK is a multi-spectral instrument, imaging the aurora in three selected emission lines simultaneously. This provides information on the energy of the precipitating electrons. The SIF (Spectrographic Imaging Facility) instrument has been used in conjunction with ASK, to give a more complete picture of the spectral characteristics of the aurora, and to determine the contamination of the emission lines by other emissions. Data from ASK and SIF is used to study the relation between the morphology and dynamics of small-scale structures in the aurora and the energy of the precipitating electrons. By comparing electron density profiles provided by EISCAT (European Incoherent SCATter) measurements with modeling results, information on characteristic energy and energy flux of the precipitating electrons can be obtained. One of the ASK channels is imaging a metastable O+ emission, which has a lifetime of 5 s. By tracing the afterglow in this channel optically a direct measure of the E × B drift and thus of the local ionospheric electric fields is provided.

Place, publisher, year, edition, pages
Stockholm: KTH , 2008. , xii, 52 p.
Series
Trita-EE, ISSN 1653-5146 ; 2008:027
Keyword [en]
Aurora
National Category
Fusion, Plasma and Space Physics
Identifiers
URN: urn:nbn:se:kth:diva-4745OAI: oai:DiVA.org:kth-4745DiVA: diva2:13751
Presentation
2008-05-23, Seminarierummet, Alfvenlaboratoriet, Teknikringen 31, Stockholm, 13:00
Opponent
Supervisors
Note
QC 20101109Available from: 2008-05-13 Created: 2008-05-13 Last updated: 2010-11-09Bibliographically approved
List of papers
1. Morphology and dynamics of aurora at fine scale: first results for the ASK instrument
Open this publication in new window or tab >>Morphology and dynamics of aurora at fine scale: first results for the ASK instrument
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2008 (English)In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 26, no 5, 1041-1048 p.Article in journal (Refereed) Published
Abstract [en]

The ASK instrument (Auroral Structure and Kinetics) is a narrow field auroral imager, providing simultaneous images of aurora in three different spectral bands at multiple frames per second resolution. The three emission species studied are O-2(+) (5620 angstrom), O+ (7319 angstrom) and O (7774 angstrom). ASK was installed and operated for the first time in an observational campaign on Svalbard, from December 2005 to March 2006. The measurements were supported by data from the Spectrographic Imaging Facility (SIF). The relation between the morphology and dynamics of the visible aurora and its spectral characteristics is studied for selected events from this period. In these events it is found that dynamic aurora is coupled to high energy electron precipitation. By studying the O-2(+)/O intensity ratio we find that some auroral filaments are caused by higher energy precipitation within regions of lower energy precipitation, whereas other filaments are the result of a higher particle flux compared to the surroundings.

Keyword
ionosphere, auroral ionosphere, particle precipitation, instruments and techniques
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-8431 (URN)10.5194/angeo-26-1041-2008 (DOI)000256224500002 ()2-s2.0-44449101276 (Scopus ID)
Note

QC 20141021

Available from: 2008-05-13 Created: 2008-05-13 Last updated: 2017-12-14Bibliographically approved
2. First direct optical observations of plasma flows using afterglow of O+ in discrete aurora
Open this publication in new window or tab >>First direct optical observations of plasma flows using afterglow of O+ in discrete aurora
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2009 (English)In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 71, no 2, 228-238 p.Article in journal (Refereed) Published
Abstract [en]

Imaging of active structured aurora in the forbidden O+ ion line at 732.0 nm provides a possibility of direct observation of plasma drifts in the topside ionosphere. The metastable O+ P-2 state has a radiative lifetime of 5 s, so the oxygen ions can be detected after the precipitation creating them has ceased. The decay time of the O+ emission is studied and modelled with a time-dependent electron transport and ion chemistry model. Four examples are given of O+ afterglow observed with the multi-spectral imager, auroral structure and kinetics (ASK), which was located near Tromso, Norway, in 2006. Estimates are given of drift velocities resulting from the analysis of the afterglow motions. Bulk plasma velocities of 340 and 720 m/s directed eastwards were found for two afterglowing arc filaments, corresponding to southward electric fields of 18 and 40 mV/m, respectively.

Keyword
Ionosphere, Plasma drift, Aurora, Oxygen ion, Electric fields, transition-probabilities, radar observations, rate coefficients, forbidden lines, electric-fields, ion drift, arcs, thermosphere, emission, airglow
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-18236 (URN)10.1016/j.jastp.2008.11.015 (DOI)000264084600006 ()2-s2.0-59249108653 (Scopus ID)
Note
QC 20100525 Tidigare titel: First direct optical observations of plasma flows in the metastable 0+ ion in discrete auroraAvailable from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
3. Using spectral characteristics to interpret auroral imaging in the 731.9 nm 0+ line
Open this publication in new window or tab >>Using spectral characteristics to interpret auroral imaging in the 731.9 nm 0+ line
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2008 (English)In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 26, no 7, 1905-1917 p.Article in journal (Refereed) Published
Abstract [en]

Simultaneous observations were made of dynamic aurora during substorm activity on 26 January 2006 with three high spatial and temporal resolution instruments: the ASK (Auroral Structure and Kinetics) instrument, SIF (Spectrographic Imaging Facility) and ESR (EISCAT Svalbard Radar), all located on Svalbard (78° N, 16.2° E). One of the narrow field of view ASK cameras is designed to detect O+ ion emission at 731.9 nm. From the spectrographic data we have been able to determine the amount of contaminating N2 and OH emission detected in the same filter. This is of great importance to further studies using the ASK instrument, when the O+ ion emission will be used to detect flows and afterglows in active aurora. The ratio of O+ to N2 emission is dependent on the energy spectra of electron precipitation, and was found to be related to changes in the morphology of the small-scale aurora. The ESR measured height profiles of electron densities, which allowed estimates to be made of the energy spectrum of the precipitation during the events studied with optical data from ASK and SIF. It was found that the higher energy precipitation corresponded to discrete and dynamic features, including curls, and low energy precipitation corresponded to auroral signatures that were dominated by rays. The evolution of these changes on time scales of seconds is of importance to theories of auroral acceleration mechanisms.

National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-8433 (URN)10.5194/angeo-26-1905-2008 (DOI)000258074300022 ()2-s2.0-47749135910 (Scopus ID)
Note

QC 20141021

Available from: 2008-05-13 Created: 2008-05-13 Last updated: 2017-12-14Bibliographically approved

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