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Cluster observations of an auroral potential and associated field-aligned current reconfiguration during thinning of the plasma sheet boundary layer
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.
KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
KTH, School of Electrical Engineering (EES), Space and Plasma Physics.ORCID iD: 0000-0003-1270-1616
2007 (English)In: Journal of Geophysical Research, ISSN 0148-0227, Vol. 112, no 1, 10.1029/2006JA011804- p.Article in journal (Refereed) Published
Abstract [en]

Cluster observations are used to illustrate the reconfiguration of an auroral potential structure encountered at the poleward boundary of the central plasma sheet within the Southern Hemisphere premidnight auroral oval. The reconfiguration from a symmetric U shape to an asymmetric S shape takes place between two consecutive crossings by Cluster spacecraft 1 and 2, moving along roughly the same orbits and separated in time by 16 min. During this time the plasma conditions poleward of the boundary changed dramatically. The fluxes of energetic electrons decreased, as did the intensities of the associated small-scale field-aligned currents (FACs) and the ambient plasma density. These changes were particularly pronounced in a narrow region adjacent to the boundary. The reconfiguration of the potential structure, and of the associated FAC system consistent with this, are consistent with the predictions by Marklund et al. (2004).

Place, publisher, year, edition, pages
2007. Vol. 112, no 1, 10.1029/2006JA011804- p.
Keyword [en]
PARALLEL ELECTRIC-FIELDS; RETURN CURRENT REGION; PARTICLE-ACCELERATION; BLACK AURORA; MAGNETOSPHERE; EVOLUTION; ARCS
National Category
Fusion, Plasma and Space Physics
Identifiers
URN: urn:nbn:se:kth:diva-7559DOI: 10.1029/2006JA011804ISI: 000243532100001Scopus ID: 2-s2.0-34547935961OAI: oai:DiVA.org:kth-7559DiVA: diva2:12622
Note
QC 20100730Available from: 2007-10-22 Created: 2007-10-22 Last updated: 2010-07-30Bibliographically 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
Opponent
Supervisors
Note
QC 20100730Available from: 2007-10-22 Created: 2007-10-22 Last updated: 2010-07-30Bibliographically approved

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Marklund, GöranKarlsson, Tomas

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