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Poloidal ULF oscillations in the dayside magnetosphere: a Cluster study
KTH, School of Electrical Engineering (EES), Space and Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
KTH, School of Electrical Engineering (EES), Space and Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
School of Pure and Applied Physics, University of KwaZulu-Natal, Durban, South Africa.
Institute for Geophysics and Extraterrestrial Physics, Technical University of Braunschweig, Germany.
2005 (English)In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 23, no 7, 2679-2686 p.Article in journal (Refereed) Published
Abstract [en]

Three ULF wave events, all occurring in the dayside magnetopshere during magnetically quiet times, are studied using the Cluster satellites. The multi-point measurements obtained from Cluster are used to determine the azimuthal wave number for the events by means of the phase shift and the azimuthal separation between the satellites. Also, the polarisation of the electric and magnetic fields is examined in a field-aligned coordinate system, which, in turn, gives the mode of the oscillations. The large-inclination orbits of Cluster allow us to examine the phase relationship between the electric and magnetic fields along the field lines. The events studied have large azimuthal wave numbers (m similar to 100), two of them have eastward propagation and all are in the poloidal mode, consistent with the large wave numbers. We also use particle data from geosynchronous satellites to look for signatures of proton injections, but none of the events show any sign of enhanced proton flux. Thus, the drift-bounce resonance instability seems unlikely to have played any part in the excitation of these pulsations. As for the drift-mirror instability we conclude that it would require an unreasonably high plasma pressure for the instability criterion to be satisfied.

Place, publisher, year, edition, pages
European Geosciences Union (EGU), 2005. Vol. 23, no 7, 2679-2686 p.
Keyword [en]
ionosphere; wave propagation; magnetospheric physics; plasma waves and instabilities; instruments and techniques
National Category
Fusion, Plasma and Space Physics
Identifiers
URN: urn:nbn:se:kth:diva-5814ISI: 000233568900037Scopus ID: 2-s2.0-27844539792OAI: oai:DiVA.org:kth-5814DiVA: diva2:10320
Note

QC 20100707

Available from: 2005-08-25 Created: 2005-08-25 Last updated: 2016-07-21Bibliographically approved
In thesis
1. Resonant Waves in the Terrestrial Magnetosphere
Open this publication in new window or tab >>Resonant Waves in the Terrestrial Magnetosphere
2005 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

Waves in the mHz frequency range are a prominent feature in the terrestrial magnetosphere. In this frequency range the waves have wavelengths comparable to the lengths of the geomagnetic field lines. The waves are then standing waves along closed field lines with endpoints in the southern and northern ionosphere. Waves play an important role in the distribution of energy in the magnetosphere and mHz waves can accelerate electrons to MeV energies and have been proposed as a driver of auroral arcs. They can also be used as a diagnostic tool for determining the plasma density. There are two important classes of these low frequency waves. One has large azimuthal wavelength and is usually associated with driving mechanisms outside the magnetosphere, such as the Kelvin-Helmholtz instability at the magnetopause. The other has small azimuthal wavelength and is associated with plasma instabilities inside the magnetosphere. Both types of waves are studied in this thesis with an emphasis on the small azimuthal wavelength waves. For the type of wave with large azimuthal wavelength there is however, a considerable debate about the driving mechanism. One recently suggested driver is coherent magnetohydrodynamic waves in the solar wind. Part of this thesis studies this experimentally and we conclude that, at least on some occasions, this driving mechanism come into play. The Cluster satellites are used to study the morphology of the waves. We demonstrate the ability of Cluster to determine the azimuthal wave number of the waves and also how the structure along the magnetic field lines can be determined. This gives information regarding the harmonic number of the standing waves, which in turn says something about the driver of the waves. We also look at possible excitation mechanisms for the small azimuthal wavelength waves.

Place, publisher, year, edition, pages
Stockholm: KTH, 2005. xi, 45 p.
Series
Trita-ALP, ISSN 1103-6613 ; 2005:05
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-400 (URN)91-7178-105-6 (ISBN)
Presentation
2005-09-12, Seminarierummet, Teknikringen 31, Stockholm, 13:00
Opponent
Supervisors
Note
QC 20101129Available from: 2005-08-25 Created: 2005-08-25 Last updated: 2010-11-29Bibliographically approved
2. Multi-point Measurements of Ultra Low Frequency Waves in the Terrestrial Magnetosphere
Open this publication in new window or tab >>Multi-point Measurements of Ultra Low Frequency Waves in the Terrestrial Magnetosphere
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Waves in the mHz frequency range are prominent features of the terrestrial magnetosphere. In this frequency range the waves have wavelengths comparable to the lengths of the geomagnetic field lines. The waves are then standing waves along closed field lines with endpoints in the southern and northern ionosphere. Waves play an important role in the distribution of energy in the magnetosphere and mHz waves can accelerate electrons to MeV energies and have been proposed as driving mechanism for auroral arcs. They can also be used as diagnostic tools for determining the plasma density. There are two important classes of these low frequency waves. One has large azimuthal wavelength and is usually associated with driving mechanisms outside the magnetosphere, such as the Kelvin-Helmholtz instability at the magnetopause. The other has small azimuthal wavelength and is associated with plasma instabilities inside the magnetosphere. Both types of waves are studied in this thesis with a slight emphasis on the large azimuthal wavelength waves. For the type of wave with large azimuthal wavelength there is however, a considerable debate about the driving mechanism. One recently suggested driver is coherent magnetohydrodynamic waves in the solar wind. Part of this thesis studies this experimentally and we conclude that, at least on some occasions, this driving mechanism comes into play. The Cluster satellites are used to study the morphology of the waves. We demonstrate the ability of Cluster to determine the azimuthal wave number of the waves and also how the structure along the magnetic field lines can be determined. This gives information regarding the harmonic number of the standing waves, which in turn says something about the driver of the waves. We also look at possible excitation mechanisms for the small azimuthal wavelength waves.

Place, publisher, year, edition, pages
Stockholm: KTH, 2007. xi, 52 p.
Series
Trita-EE, ISSN 1653-5146 ; 2007:014
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-4404 (URN)978-91-7178-615-9 (ISBN)
Public defence
2007-06-08, Sal F3, KTH, Lindstedtsvägen 26, Stockhol, 10:00
Opponent
Supervisors
Note
QC 20100707Available from: 2007-05-29 Created: 2007-05-29 Last updated: 2010-07-07Bibliographically approved

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