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Cluster satellite observations of mHz pulsations in the dayside magnetosphere
KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
Institute for Geophysics and Extraterrestrial Physics, Technical University of Braunschweig, Tyskland.
2006 (Engelska)Ingår i: Advances in Space Research, ISSN 0273-1177, E-ISSN 1879-1948, Vol. 38, nr 8, s. 1730-1737Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

On 17 August 2002 the Cluster spacecraft moved through the dayside magnetosphere. Between 16:00 and 18:30 LIT clear monochromatic oscillations are seen in both electric field and magnetometer data. The frequency is 4.2 mHz in the spacecraft frame of reference. The oscillations have a clear spatial localisation. The magnetic field oscillations are radially polarised in the plane perpendicular to the background magnetic field, indicating that the wave is in the poloidal mode. From the difference in phase between the satellites we estimate the azimuthal wave number, in, to be about 130, consistent with the magnetic field polarisation. The frequency is stable for different L-values as well as over time. From the value of in, the Doppler shift due to satellite motion is estimated to 0.5 mHz. By looking at the phase of the electric and the magnetic field close to the equator we conclude that the oscillations are in a mode with an odd number of half wavelengths between the two ionospheres.

Ort, förlag, år, upplaga, sidor
2006. Vol. 38, nr 8, s. 1730-1737
Nyckelord [en]
ULF pulsations
Nationell ämneskategori
Fusion, plasma och rymdfysik
Identifikatorer
URN: urn:nbn:se:kth:diva-5813DOI: 10.1016/j.asr.2005.04.103ISI: 000202988500024Scopus ID: 2-s2.0-33845991191OAI: oai:DiVA.org:kth-5813DiVA, id: diva2:10319
Anmärkning

QC 20100707. Konferens: 35th COSPAR Scientific Assembly Paris, FRANCE, JUL 18-25, 2004 Comm Space Res.

Tillgänglig från: 2005-08-25 Skapad: 2005-08-25 Senast uppdaterad: 2017-12-14Bibliografiskt granskad
Ingår i avhandling
1. Resonant Waves in the Terrestrial Magnetosphere
Öppna denna publikation i ny flik eller fönster >>Resonant Waves in the Terrestrial Magnetosphere
2005 (Engelska)Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
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.

Ort, förlag, år, upplaga, sidor
Stockholm: KTH, 2005. s. xi, 45
Serie
Trita-ALP, ISSN 1103-6613 ; 2005:05
Nationell ämneskategori
Fusion, plasma och rymdfysik
Identifikatorer
urn:nbn:se:kth:diva-400 (URN)91-7178-105-6 (ISBN)
Presentation
2005-09-12, Seminarierummet, Teknikringen 31, Stockholm, 13:00
Opponent
Handledare
Anmärkning
QC 20101129Tillgänglig från: 2005-08-25 Skapad: 2005-08-25 Senast uppdaterad: 2010-11-29Bibliografiskt granskad
2. Multi-point Measurements of Ultra Low Frequency Waves in the Terrestrial Magnetosphere
Öppna denna publikation i ny flik eller fönster >>Multi-point Measurements of Ultra Low Frequency Waves in the Terrestrial Magnetosphere
2007 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
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.

Ort, förlag, år, upplaga, sidor
Stockholm: KTH, 2007. s. xi, 52
Serie
Trita-EE, ISSN 1653-5146 ; 2007:014
Nationell ämneskategori
Fusion, plasma och rymdfysik
Identifikatorer
urn:nbn:se:kth:diva-4404 (URN)978-91-7178-615-9 (ISBN)
Disputation
2007-06-08, Sal F3, KTH, Lindstedtsvägen 26, Stockhol, 10:00
Opponent
Handledare
Anmärkning
QC 20100707Tillgänglig från: 2007-05-29 Skapad: 2007-05-29 Senast uppdaterad: 2010-07-07Bibliografiskt granskad

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