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Dynamics and characteristics of black aurora as observed by high resolution ground-based imagers and radar
KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
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
School of Physics and Astronomy, University of Southampton, UK.
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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.

Place, publisher, year, edition, pages
2011. Vol. 32, no 11, 2973-2985 p.
Keyword [en]
Remote Sensing, Imaging Science & Photographic Technology
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
URN: urn:nbn:se:kth:diva-24906DOI: 10.1080/01431161.2010.541517ISI: 000293223900003ScopusID: 2-s2.0-79960046158OAI: diva2:354132
Updated from accepted to published 24 Jun 2011. QC 20101030Available from: 2010-09-30 Created: 2010-09-30 Last updated: 2011-12-01Bibliographically approved
In thesis
1. 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. xx, 90 p.
Trita-EE, ISSN 1653-5146 ; 2010:040
National Category
Fusion, Plasma and Space Physics Atom and Molecular Physics and Optics
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)
QC 20101001Available from: 2010-10-01 Created: 2010-09-30 Last updated: 2010-10-01Bibliographically approved

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