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Sunward propagating Pc5 waves observed on the post-midnight magnetospheric flank
KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
Institute for Geophysics and Extraterrestrial Physics, Technical University of Braunschweig, Germany.
Institute for Geophysics and Extraterrestrial Physics, Technical University of Braunschweig, Germany.
2008 (English)In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 26, no 6, 1567-1579 p.Article in journal (Refereed) Published
Abstract [en]

The overall focus on the driver of toroidal Pc5 waves has been on processes located at or acting on the dayside magnetopause and dayside flanks of the magnetosphere. These processes can generate waves that propagate tailward in the magnetosphere. However, an increasing number of studies, both theoretical and experimental, have looked at waves propagating sunward and that are caused by processes in the magnetotail. Here we present an ultra low frequency (ULF) wave observed in the post-midnight/morning sector of the magnetosphere at L=16 R-E. The wave has a toroidal mode polarization. We estimate the azimuthal wave number to m=3, consistent with a toroidal mode type pulsation. The positive sign indicates that the wave is propagating sunward and this is confirmed by looking at the Poynting flux of the wave. The frequency of the wave is not constant with time but shows a small increase in the beginning of the event up to over 2.0 mHz. Then the frequency decreases to 1.0 mHz. This decrease coincides with a drop in the total magnetic field strength and we speculate if this is related to an observed reversal of the sign of the interplanetary magnetic field (IMF) By-component. This event occurs during relatively quiet magnetospheric conditions with a solar wind speed of approximately 400 km/s. Thus this event is highly likely to be driven by a source in the magnetotail and the change in frequency is an excellent example that the frequency of an ULF wave may be modulated by changes of the plasma parameters on the resonant field line.

Place, publisher, year, edition, pages
2008. Vol. 26, no 6, 1567-1579 p.
Keyword [en]
magnetospheric physics; MHD waves and instabilities; solar wind-magnetosphere interactions
National Category
Fusion, Plasma and Space Physics
Identifiers
URN: urn:nbn:se:kth:diva-7223ISI: 000256594000023Scopus ID: 2-s2.0-45149086648OAI: oai:DiVA.org:kth-7223DiVA: diva2:12166
Note
QC 20100707. Uppdaterad från Submitted till Published 20100707.Available from: 2007-05-29 Created: 2007-05-29 Last updated: 2010-07-07Bibliographically approved
In thesis
1. 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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