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Magnetosphere-ionosphere coupling during periods of extended high auroral activity: A case study
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
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.
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2008 (English)In: Annales Geophysicae, ISSN 0992-7689, Vol. 26, 583-591 p.Article in journal (Refereed) Published
Abstract [en]

Results are presented from a case study of a plasma boundary crossing by the Cluster spacecraft during an extended period of high auroral activity. The boundary between the magnetotail lobe region of the Southern Hemisphere and the plasma sheet boundary layer, was characterized by intense electric and magnetic field variations, structured upward accelerated ion beams, narrow-scale large field-aligned Poynting fluxes directed upward away from the ionosphere, and a relatively sharp plasma density gradient. The observations are shown to be consistent with the concept of a multi-layered boundary with temporal and/or spatial variations in the different layers. H+ and O+ ion beams are seen to be accelerated upwards both by means of a field-aligned electric field and by magnetic pumping caused by large-amplitude and low-frequency electric field fluctuations. The peak energy of the ion beams may here be used as a diagnostic tool for the temporal evolution of the spatial structures, since the temporal changes occur on a time-scale shorter than the times-of-flight of the detected ion species. The case study also shows the boundary region to be mainly characterized by a coupling of the detected potential structures to the low ionosphere during the extended period of high auroral activity, as indicated by the intense field-aligned Poynting fluxes directed upward away from the ionosphere.

Place, publisher, year, edition, pages
2008. Vol. 26, 583-591 p.
Keyword [en]
aurora; boundary layer; coupling; electric field; ionosphere; magnetic field; magnetosphere; plasma; Southern Hemisphere; spatial variation; temporal variation
National Category
Fusion, Plasma and Space Physics
Identifiers
URN: urn:nbn:se:kth:diva-14246ISI: 000255364900016Scopus ID: 2-s2.0-41449084279OAI: oai:DiVA.org:kth-14246DiVA: diva2:331865
Note
QC 20100727Available from: 2010-07-27 Created: 2010-07-27 Last updated: 2010-12-06Bibliographically approved
In thesis
1. Auroral electrodynamics of plasma boundary regions
Open this publication in new window or tab >>Auroral electrodynamics of plasma boundary regions
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The electrodynamic coupling between the auroral ionosphere and the magnetosphere is the main subject of this thesis. Satellite measurements of electric and magnetic fields and of charged particles are used to explore three distinct plasma boundaries, magnetically linked to the nightside auroral ionosphere. These boundaries are the inner edge of the plasma sheet (PS), and the inner and the outer edges of the plasma sheet boundary layer (PSBL).

Strong ionospheric electric fields with amplitudes up to 400 mV/m may be observed in the subauroral ionosphere, in the vicinity of the ionospheric projection of the PS inner edge. Intense and dynamic auroral electric fields with local magnitudes up to 150 mV/m associated with upward ion beams and field-aligned currents are observed for the events treated here, at the inner and outer boundaries of the PSBL at an altitude of about 4-5 Earth radii, well above the acceleration region. Subauroral and auroral electric fields are the two main subjects of this thesis.

Subauroral ion drifts (SAID) are associated with poleward electric fields, occurring predominantly in the premidnight region during the substorm recovery phase. The recently revealed abnormal subauroral ion drifts (ASAID) are associated with equatorward electric fields, occurring during extended periods of low auroral activity. The results indicate that the generation mechanism of SAID can neither be regarded as a pure voltage generator nor a pure current generator, but having certain characteristics of both generator types. Ionospheric feedback appears to play a major role for the development and maintenance of the SAID electric fields. The formation of ASAID is proposed to result from the proximity and interaction between different plasma boundaries of the innermost magnetosphere during extended periods of low auroral activity.

The auroral electric fields observed in the upward current region at the PSBL inner and outer edges are associated with upward parallel electric fields, which partially decouple the high-altitude electric fields from the ionosphere. This is in contrast to the subauroral electric fields which are coupled. Multi-point measurements provided by the Cluster mission show that the observed electric fields are highly variable in space and time, revealing various types of acceleration processes. However, they appear to be tied to the boundary where they are originally formed. A case is  presented where they are associated with large electromagnetic energy fluxes directed upward away from the ionosphere. The interaction between the magnetosphere and ionosphere, being more pronounced at plasma boundary regions, is important for the understanding of the formation and regulation of the highly structured auroral electric fields observed in the upward current region.

Place, publisher, year, edition, pages
Stockholm: KTH, 2009. xii, 74 p.
Series
Trita-EE, ISSN 1653-5146 ; 2009:027
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-10446 (URN)978-91-7415-317-0 (ISBN)
Public defence
2009-05-29, Sal F3, KTH, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20100727Available from: 2009-05-14 Created: 2009-05-14 Last updated: 2010-07-27Bibliographically approved

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Karlsson, TomasMarklund, Göran TLindqvist, Per-Arne

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