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Subauroral electric fields observed by the Freja satellite: A statistical study
KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.ORCID iD: 0000-0003-1270-1616
KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.ORCID iD: 0000-0002-1594-1861
KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
1998 (English)In: JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, ISSN 0148-0233, Vol. 103, no A3, 4327-4341 p.Article in journal (Refereed) Published
Abstract [en]

Over 12 months of Freja electric field data have been scanned for subauroral electric fields (SAEF) to enable a comprehensive study of the ionospheric signatures of such electric fields. SAEF are encountered from 1800 to 0200 MLT in agreement with an earlier study. However, a large majority of the SAEF are encountered at a time slightly premidnight (2200 - 2300 MLT), with rather few occurrences before 2000 MLT and after 2400 MLT. Furthermore, the strength of the subauroral electric field is generally much larger for events close to 2200 MLT than for other events. The data confirm that SAEF occur during the substorm recovery phase but also show that SAEF occur earlier during recovery when located close to 2200 MLT than at other local times. The dependence on season and geomagnetic activity is studied, and it is found that the SAEF are more commonly observed at times of high activity when the subauroral electric fields are also generally stronger, except close to winter solstice, when strong electric fields are observed during low activity. The potentials associated with the SAEF and the relation to interplanetary magnetic field B-y are also studied. The observations are discussed in context with substorm-related field-aligned currents and the midlatitude trough, and we present evidence that support and refine one of the proposed production mechanisms.

Place, publisher, year, edition, pages
1998. Vol. 103, no A3, 4327-4341 p.
Keyword [en]
AURORAL ION PRECIPITATION, ALIGNED CURRENTS, F-REGION, CONVECTION, MODEL, IONOSPHERE, LATITUDES, BOUNDARY, DRIFTS, TROUGH
National Category
Fusion, Plasma and Space Physics
Identifiers
URN: urn:nbn:se:kth:diva-13713ISI: 000072401200032OAI: oai:DiVA.org:kth-13713DiVA: diva2:326732
Note
QC 20100624 NR 20140804Available from: 2010-06-24 Created: 2010-06-24 Last updated: 2012-03-19Bibliographically approved
In thesis
1. Auroral Electric Fields From Satellite Observations and Numerical Modelling
Open this publication in new window or tab >>Auroral Electric Fields From Satellite Observations and Numerical Modelling
2001 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is about electrodynamics of thehigh-latitude/auroral region of near-Earth space. The work ismainly based on electric field measurements made by the doubleprobe instrument on the Freja satellite at altitudes ofapproximately 800-1700 km, together with measurements fromother instruments on the same satellite, and ground-basedinstrumentation. A useful tool for interpreting observationaldata is also numerical modelling, and this is the subject ofpart of the work. The electric field measurements address threesubjects. The first one is that of very intense, divergingelectric fields at Freja altitude. Statistics and case studiesshow that these structures have scale-sizes of the order of 1km, and are associated with regions devoid of electronprecipitation (which at times can be identified with theoptical phenomenon of black aurora), with downward currents,ion heating, density depletions, and upward acceleratedelectron beams. A numerical model is used to study theionospheric response to intense small-scale current systems. Itis shown that on time scales of the order of 1 minute, deepdensity cavities and enhancements of the electric fieldresults. The second subject is the electrodynamics of thewestward traveling surge (WTS) and other large-scale auroralspirals. Freja measurements show that the electric field isdirected towards the surge/spiral center, and that the surgehead is associated with extremely intense, small-scale,converging electric fields, and field-aligned currents. Datasuggest that a significant part of the upward current of thesurge head is closed by localized, downward-directed currents,whereas no clear signature of a Cowling channel feeding thecurrent to the surge head from distributed downward currents inthe wake of the surge is observed. The third type ofmeasurements concerns the phenomenon of subauroral ion drifts(SAID), or equivalently subauroral electric fields (SAEF). Acomprehensive statistics shows the distribution in local timeand latitude of the SAID, and their correlation withgeomagnetic activity. It is concluded that the SAID areassociated with the low-conductivity region of the mid-latitudetrough, and that they may be a consequence of closure ofsubstorm-related currents through this region, which may becomeeven more low-conducting by the ionospheric response to theapplied current and electric field. Finally a new formulationof a classification scheme of auroral arc-associated electricfields is given. It is shown that this generalization enables aflexible way of modelling and predicting the arc-associatedfield in various situations.

Keywords: Satellite measurements, electric fields,ionosphere, magnetosphere, diverging electric fields, downwardcurrent region, black aurora, westward traveling surge, auroralbulge, subauroral ion drifts (SAID), subauroral electric fields(SAEF), mid-latitude trough, numerical modelling, auroral arcclassification, auroral arc-associated electric field.

Place, publisher, year, edition, pages
Stockholm: KTH, 2001. 35 p.
Keyword
Satellite measurements, electric fields, ionosphere, magnetosphere, diverging electric fields, downward current region, black aurora, westward travelling surge, auroral bulge, subauroral ion drifts (SAID), subauroral electric fields (SAEF), mid-latit
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-3130 (URN)
Public defence
2001-04-30, 00:00 (English)
Note
QC 20100624Available from: 2001-04-25 Created: 2001-04-25 Last updated: 2010-06-24Bibliographically approved

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