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Statistical study on the occurrence of ASAID electric fields
KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.ORCID-id: 0000-0003-1270-1616
KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.ORCID-id: 0000-0002-1594-1861
2010 (Engelska)Ingår i: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 28, nr 2, s. 439-448Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The first statistical results on the occurrence of abnormal subauroral ion drifts (ASAID) are presented based on electric and magnetic field measurements from the low-altitude Astrid-2 satellite. ASAID are narrow regions of rapid eastward ion drifts observed in the subauroral ionosphere. They correspond to equatorward-directed electric fields with peak amplitudes seen to vary between 45 mV/m and 185 mV/m, and with latitudinal extensions between 0.2 degrees and 1.2 degrees Corrected Geomagnetic Latitude (CGLat), reaching in some cases up to 3.0 degrees CGLat. Opposite to subauroral ion drifts (SAID) that are known to be substorm-related, ASAID are seen to occur predominantly during extended periods of low substorm activity. Our results show that ASAID are located in the vicinity of the equatorward edge of the auroral oval, mainly in the postmidnight sector between 23:00 and 03:00 magnetic local time. They are associated with a local current system with the same scale-size as the corresponding ASAID, composed by a region of downward field-aligned currents (FACs) flowing in the ASAID poleward side, and a region of upward flowing FACs in the equatorward side. The FACs have densities between 0.5 and 2.0 mu A/m(2). The data suggest that ASAID do not contribute significantly to the reduction of the ionospheric conductivity. ASAID are seen to have life times of at least 3.5 h. A discussion on possible mechanisms for the generation of ASAID is presented. We speculate that the proximity of the electron to the ion plasma sheet inner boundaries and of the plasmapause to the ring current outer edge, during extended quiet times, is an important key for the understanding of the generation of ASAID electric fields.

Ort, förlag, år, upplaga, sidor
2010. Vol. 28, nr 2, s. 439-448
Nyckelord [en]
Ionosphere, Electric fields and currents, Ionosphere-magnetosphere interactions, Mid-latitude ionosphere
Nationell ämneskategori
Fusion, plasma och rymdfysik
Identifikatorer
URN: urn:nbn:se:kth:diva-14247DOI: 10.5194/angeo-28-439-2010ISI: 000274995800012Scopus ID: 2-s2.0-76749156148OAI: oai:DiVA.org:kth-14247DiVA, id: diva2:331866
Anmärkning
QC 20100727Tillgänglig från: 2010-07-27 Skapad: 2010-07-27 Senast uppdaterad: 2017-12-12Bibliografiskt granskad
Ingår i avhandling
1. Auroral electrodynamics of plasma boundary regions
Öppna denna publikation i ny flik eller fönster >>Auroral electrodynamics of plasma boundary regions
2009 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
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.

Ort, förlag, år, upplaga, sidor
Stockholm: KTH, 2009. s. xii, 74
Serie
Trita-EE, ISSN 1653-5146 ; 2009:027
Nationell ämneskategori
Fusion, plasma och rymdfysik
Identifikatorer
urn:nbn:se:kth:diva-10446 (URN)978-91-7415-317-0 (ISBN)
Disputation
2009-05-29, Sal F3, KTH, Lindstedtsvägen 26, Stockholm, 10:00 (Engelska)
Opponent
Handledare
Anmärkning
QC 20100727Tillgänglig från: 2009-05-14 Skapad: 2009-05-14 Senast uppdaterad: 2010-07-27Bibliografiskt granskad

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Karlsson, TomasMarklund, Göran T

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