Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Multi-spectral analysis of fine scale aurora
KTH, School of Electrical Engineering (EES), Space and Plasma Physics.ORCID iD: 0000-0001-5596-346X
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. , xx, 90 p.
Series
Trita-EE, ISSN 1653-5146 ; 2010:040
National Category
Fusion, Plasma and Space Physics Atom and Molecular Physics and Optics
Identifiers
URN: urn:nbn:se:kth:diva-24907ISBN: 978-91-7415-749-9 (print)OAI: oai:DiVA.org:kth-24907DiVA: diva2:354186
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
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
Show others...
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: 2014-10-21Bibliographically approved
2. 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
Show others...
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: 2014-10-21Bibliographically approved
3. 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
Show others...
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
4. Simultaneous observations of small multi-scale structures in an auroral arc
Open this publication in new window or tab >>Simultaneous observations of small multi-scale structures in an auroral arc
Show others...
2010 (English)In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 72, 633-637 p.Article in journal (Refereed) Published
Abstract [en]

Auroral arcs can develop small-scale distortions known as vortex streets or curls. Other common and somewhat larger spatially periodic distortions are auroral folds. In this event study we present simultaneous wide and narrow field imager observations of a third kind of structuring, on even smaller spatial scales. Boundary undulations, or “ruffs”, have been observed to form on the edge of an auroral arc and they occur superimposed on curls, folds or at times of auroral shear. The undulations typically have wavelengths of less than 3 km and amplitudes of less than 800 m. They are observed to move on the edge of the arc, with velocities of about 11 km/s. These observations, with multi-scale deformations, reveal a much more intricate structuring of auroral arcs than previously found.

Keyword
Auroral fine structure, Auroral curls and folds, Instruments and techniques, Plasma instabilities
National Category
Fusion, Plasma and Space Physics Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-24905 (URN)10.1016/j.jastp.2010.01.014 (DOI)000277677300009 ()2-s2.0-77952956058 (Scopus ID)
Note
QC 20100930Available from: 2010-09-30 Created: 2010-09-30 Last updated: 2017-12-12Bibliographically approved
5. Dynamics and characteristics of black aurora as observed by high resolution ground-based imagers and radar
Open this publication in new window or tab >>Dynamics and characteristics of black aurora as observed by high resolution ground-based imagers and radar
Show others...
2011 (English)In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 32, no 11, 2973-2985 p.Article in journal (Refereed) Published
Abstract [en]

High-resolution, multi-spectral data from the ground-based low-light auroral imager ASK (Auroral Structure and Kinetics) are used to characterize the fine structure of black aurora. Sixteen events comprising sheared and unsheared black arcs, as well as black patches and rings, constitute the analysed dataset. Simultaneous measurements of emissions caused by high- and low-energy precipitation make it possible to relate the characteristics of different black structures to the energy of the precipitating electrons. The reductions of high-energy particles versus low-energy particles in the black regions compared to the diffuse background are investigated for the different forms of black aurora. Two separate mechanisms have been suggested to cause black aurora. The larger reduction of high-energy precipitation within the fine-scale black structures discussed here favours a magnetospheric mechanism that blocks high-energy electrons from being scattered into the loss cone. European Incoherent SCATter radar (EISCAT) electron density profiles are available for one of the nights, and are compared to the optical measurements.

Keyword
Remote Sensing, Imaging Science & Photographic Technology
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-24906 (URN)10.1080/01431161.2010.541517 (DOI)000293223900003 ()2-s2.0-79960046158 (Scopus ID)
Note
Updated from accepted to published 24 Jun 2011. QC 20101030Available from: 2010-09-30 Created: 2010-09-30 Last updated: 2017-12-12Bibliographically approved

Open Access in DiVA

fulltext(16786 kB)261 downloads
File information
File name FULLTEXT01.pdfFile size 16786 kBChecksum SHA-512
dbfa193aaec425ae5c3b9502274cb1215daf63e8b5f65854456c3b611ef3a9974c9a79e7d6388a158a35a97201612564f53c1918463b267abfc09c328f8ad3c8
Type fulltextMimetype application/pdf

Authority records BETA

Dahlgren, Hanna

Search in DiVA

By author/editor
Dahlgren, Hanna
By organisation
Space and Plasma Physics
Fusion, Plasma and Space PhysicsAtom and Molecular Physics and Optics

Search outside of DiVA

GoogleGoogle Scholar
Total: 261 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 691 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf