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Using spectral characteristics to interpret auroral imaging in the 731.9 nm 0+ line
KTH, School of Electrical Engineering (EES), Space and Plasma Physics.ORCID iD: 0000-0001-5596-346X
KTH, School of Electrical Engineering (EES), Space and Plasma Physics.ORCID iD: 0000-0003-2422-5426
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2008 (English)In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 26, no 7, p. 1905-1917Article 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.

Place, publisher, year, edition, pages
2008. Vol. 26, no 7, p. 1905-1917
National Category
Fusion, Plasma and Space Physics
Identifiers
URN: urn:nbn:se:kth:diva-8433DOI: 10.5194/angeo-26-1905-2008ISI: 000258074300022Scopus ID: 2-s2.0-47749135910OAI: oai:DiVA.org:kth-8433DiVA, id: diva2:13750
Note

QC 20141021

Available from: 2008-05-13 Created: 2008-05-13 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Fine-scale morphology and spectral characteristics of active aurora
Open this publication in new window or tab >>Fine-scale morphology and spectral characteristics of active aurora
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. p. xii, 52
Series
Trita-EE, ISSN 1653-5146 ; 2008:027
Keyword
Aurora
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-4745 (URN)
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
2. Multi-spectral analysis of fine scale aurora
Open this publication in new window or tab >>Multi-spectral analysis of fine scale aurora
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The Aurora Borealis is the visible manifestation of the complex plasma interaction between the solar wind and the Earth's magnetosphere and ionosphere. Ground based and in situ measurements demonstrate a prevalence of dynamic fine structure within auroral displays, with spatial scales down to tens of metres and time variations occurring on a fraction of a second.The fine-scale morphology is related to structuring of auroral currents and electric fields and detailed spatial, spectral and temporal observations of the aurora are crucial in understanding the electrodynamic processes taking place in the ionosphere and in its coupling to the magnetosphere.

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 emissions 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 degree of contaminating emissions present in the same spectral interval as the emission lines observed by ASK.

Data from ASK and SIF are 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) radar measurements with modeling results, information on the characteristic energy and the 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 about 5 s. By tracing the afterglow in this channel optically a direct measure of the E x B drift is obtained from which the local ionospheric electric field can be calculated. ASK data has also been used to analyse the properties of a distorted auroral arc, in which auroral structuring was found to take place simultaneously at different spatial scales. The smallest features, 'ruffs', are undulations found to develop on the edge of an auroral curl, fold or shear. Detailed optical studies of black aurora, including both the type which is associated with plasma shear motions and no or weak shear motions were conducted from ASK data, to investigate the spectral properties and fine scale morphology of the black structures and to shed light on the processes behind this phenomenon.

Place, publisher, year, edition, pages
Stockholm: KTH, 2010. p. xx, 90
Series
Trita-EE, ISSN 1653-5146 ; 2010:040
National Category
Fusion, Plasma and Space Physics Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-24907 (URN)978-91-7415-749-9 (ISBN)
Public defence
2010-10-22, H1, Teknikringen 33, KTH, Stockholm, 13:15 (English)
Opponent
Supervisors
Note
QC 20101001Available from: 2010-10-01 Created: 2010-09-30 Last updated: 2010-10-01Bibliographically approved

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Dahlgren, HannaIvchenko, NickolayMarklund, Göran

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