Poloidal ULF oscillations in the dayside magnetosphere: a Cluster study
2005 (English)In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 23, no 7, 2679-2686 p.Article in journal (Refereed) Published
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.
ionosphere; wave propagation; magnetospheric physics; plasma waves and instabilities; instruments and techniques
Fusion, Plasma and Space Physics
IdentifiersURN: urn:nbn:se:kth:diva-5814ISI: 000233568900037ScopusID: 2-s2.0-27844539792OAI: oai:DiVA.org:kth-5814DiVA: diva2:10320
QC 201007072005-08-252005-08-252016-07-21Bibliographically approved