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Ann. Geophys., 26, 1805-1817, 2008
www.ann-geophys.net/26/1805/2008/
© European Geosciences Union 2008
Spatio-temporal structure of a poloidal Alfvén wave detected by Cluster adjacent to the dayside plasmapause
S. Schäfer1, K. H. Glassmeier1, P. T. I. Eriksson2, P. N. Mager3, V. Pierrard4, K. H. Fornaçon1, and L. G. Blomberg2
1Institut für Geophysik und extraterrestrische Physik, TU Braunschweig, Germany
2Space and Plasma Physics, School of Electrical Engineering, Royal Institute of Technology Stockholm, Sweden
3Inst. of Solar-Terrestrial Physics (ISTP), State Academy of Science, Siberian Branch, Irkutsk, P.O. Box 291, 664033, Russia
4Belgian Institute for Space Aeronomy, Brussels, Belgium
Abstract. A case study of a poloidal ULF pulsation near the dayside
plasmapause is presented based on Cluster observations of magnetic
and electric fields. The pulsation is detected close to the
magnetic equatorial plane at L shells L=[4.4, 4.6] and
oscillates with a frequency of f=23 mHz. Investigating
the wave energy flux reveals the standing wave nature of the
observed pulsation. An estimation of the azimuthal wave number
exposes a narrow azimuthal structure of the wave field with m≈160. Spatial and temporal characteristics of the
pulsation are analyzed in detail by representing data in a field
line related coordinate system and a range-time-intensity
representation. This allows an estimation of both the spatial
extension of the wave field in the radial direction and its temporal
decay rate. The analysis furthermore indicates that the same
field lines are excited to a standing wave oscillation twice.
Furthermore an accurate identification of a phase jump of the wave
field across L shells is possible. Comparing the radial
localization of the detected wave with theoretically expected
field line eigenfrequencies reveals that the wave field is
confined in the Alfvén resonator at the outer edge of the
plasmapause.
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