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A statistical study of intense electric fields at 4-7 R-E geocentric distance using Cluster
KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.ORCID iD: 0000-0003-1270-1616
KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.ORCID iD: 0000-0002-1594-1861
KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
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2005 (English)In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 23, no 7, 2579-2588 p.Article in journal (Refereed) Published
Abstract [en]

Intense high-latitude electric fields (> 150 mV/m mapped to ionospheric altitude) at 4-7 R-E geocentric distance have been investigated in a statistical study, using data from the Cluster satellites. The orbit of the Cluster satellites limits the data collection at these altitudes to high latitudes, including the poleward part of the auroral oval. The occurrence and distribution of the selected events have been used to characterize the intense electric fields and to investigate their dependance on parameters such as MLT, CGLat, altitude, and also K-p. Peaks in the local time distribution are found in the evening to morning sectors but also in the noon sector, corresponding to cusp events. The electric field intensities decrease with increasing latitude in the region investigated (above 60 CGLat). A dependence on geomagnetic activity is indicated since the probability of finding an event increases up to K-p=5-6. The scales sizes are in the range up to 10 km (mapped to ionospheric altitude) with a maximum around 4-5 km, consistent with earlier findings at lower altitudes and Cluster event studies. The magnitudes of the electric fields are inversely proportional to the scale sizes. The type of electric field structure (convergent or divergent) is consistent with the FAC direction for a subset of events with electric field intensities in the range 500-1000 mV/m and with clear bipolar signatures. The FAC directions are also consistent with the Region 1 and NBZ current systems, the latter of which prevail only during northward IMF conditions. For scale sizes less than 2 km the majority of the events were divergent electric field structures. Both converging and diverging electric fields were found throughout the investigated altitude range (4-7 RE geocentric distance).

Place, publisher, year, edition, pages
2005. Vol. 23, no 7, 2579-2588 p.
Keyword [en]
Magnetospheric physics (Electric fields; Auroral phenomena; Magnetosphere-ionosphere interactions)
National Category
Fusion, Plasma and Space Physics
Identifiers
URN: urn:nbn:se:kth:diva-7557DOI: 10.5194/angeo-23-2579-2005ISI: 000233568900028Scopus ID: 2-s2.0-27844562666OAI: oai:DiVA.org:kth-7557DiVA: diva2:12620
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
Opponent
Supervisors
Note
QC 20100730Available from: 2007-10-22 Created: 2007-10-22 Last updated: 2010-07-30Bibliographically approved

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Karlsson, TomasMarklund, GöranLindqvist, Per-Arne

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