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On the profile of intense high-altitude auroral electric fields at magnetospheric boundaries
KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
KTH, School of Electrical Engineering (EES), Space and Plasma Physics.ORCID iD: 0000-0002-1594-1861
KTH, School of Electrical Engineering (EES), Space and Plasma Physics.ORCID iD: 0000-0003-1270-1616
KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
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2006 (English)In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 24, no 6, 1713-1723 p.Article in journal (Refereed) Published
Abstract [en]

The profile of intense high-altitude electric fields on auroral field lines has been studied using Cluster data. A total of 41 events with mapped electric field magnitudes in the range between 0.5-1 V/m were examined, 27 of which were co-located with a plasma boundary, defined by gradients in particle flux, plasma density and plasma temperature. Monopolar electric field profiles were observed in 11 and bipolar electric field profiles in 16 of these boundary-associated electric field events. Of the monopolar fields, all but one occurred at the polar cap boundary in the late evening and midnight sectors, and the electric fields were typically directed equatorward, whereas the bipolar fields all occurred at plasma boundaries clearly within the plasma sheet. These results support the prediction by Marklund et al. (2004), that the electric field profile depends on whether plasma populations, able to support intense field-aligned currents and closure by Pedersen currents, exist on both sides, or one side only, of the boundary.

Place, publisher, year, edition, pages
2006. Vol. 24, no 6, 1713-1723 p.
Keyword [en]
aurora; boundary layer; electric field; magnetosphere; plasma
National Category
Fusion, Plasma and Space Physics
Identifiers
URN: urn:nbn:se:kth:diva-7558DOI: 10.5194/angeo-24-1713-2006ISI: 000239724500020Scopus ID: 2-s2.0-33751071835OAI: oai:DiVA.org:kth-7558DiVA: diva2:12621
Note
QC 20100730Available from: 2007-10-22 Created: 2007-10-22 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Investigations of auroral electric fields and currents
Open this publication in new window or tab >>Investigations of auroral electric fields and currents
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The Cluster spacecraft have been used to investigate auroral electric fields and field-aligned currents (FACs) at geocentric distances between 4 and 7 Re. The electric fields have been measured by the EFW instrument, consisting of two pairs of spherical probes, and the FACs have been calculated from measurements of the magnetic field by the FGM fluxgate magnetometer. CIS ion and PEACE electron measurements have also been used. Event studies as well as statistical studies have been used to determine the characteristics of the auroral electric fields. In two events where regions of both spatial and temporal electric field variations could be identified, the quasi-static electric fields were, compared to the Alfvén waves, found to be more intense and contribute more to the downward Poynting flux. With the use of the four Cluster spacecraft, the quasi-static electric field structures were found to be relatively stable on the time scale of at least half a minute. Quasi-static electric fields were found throughout the altitude range covered by Cluster in the auroral region. The electric field structures were found both in the upward and downward current regions. Bipolar and monopolar electric fields, corresponding to U- and S-shaped potential structures, have been found at different plasma boundaries, consistent with the view that the plasma conditions and the geometry of the current system are related to the shape of the electric field. The type of the bipolar electric field structures (convergent or divergent) was further found to be consistent with the FAC direction. The typical scale sizes of the electric field structures have been determined to be between 4 and 5 km, when mapped to ionospheric altitude. The most intense FACs associated with intense electric fields were found for small FAC widths. The widths of upward and downward FACs were similar.

Place, publisher, year, edition, pages
Stockholm: KTH, 2007. vii, 48 p.
Series
Trita-EE, ISSN 1653-5146 ; 2007:056
Keyword
auroral physics, auroral electric fields, auroral potential structures, auroral particle acceleration
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-4512 (URN)978-91-7178-761-3 (ISBN)
Public defence
2007-11-09, F3, Lindstedsvägen 26, Stockholm, 10:00
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Note
QC 20100730Available from: 2007-10-22 Created: 2007-10-22 Last updated: 2010-07-30Bibliographically approved

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Marklund, GöranKarlsson, TomasLindqvist, Per-Arne

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