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Ann. Geophys., 25, 1011-1024, 2007
www.ann-geophys.net/25/1011/2007/
© European Geosciences Union 2007
Spatial and temporal characteristics of poloidal waves in the terrestrial plasmasphere: a CLUSTER case study
S. Schäfer1, K. H. Glassmeier1, P. T. I. Eriksson2, V. Pierrard3, 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
3Belgian Institute for Space Aeronomy, Brussels, Belgium
Abstract. Oscillating magnetic field lines are frequently observed by spacecraft in the
terrestrial and other planetary magnetospheres. The CLUSTER mission is a very
suitable tool to further study these Alfvén waves as the four CLUSTER
spacecraft provide for an opportunity to separate spatial and temporal
structures in the terrestrial magnetosphere. Using a large scaled configuration
formed by the four spacecraft we are able to detect a poloidal
Ultra-Low-Frequency (ULF) pulsation of the magnetic and electric field in order
to analyze its temporal and spatial structures. For this purpose the
measurements are transformed into a specific field line related coordinate
system to investigate their specific amplitude pattern depending on the path of
the CLUSTER spacecraft across oscillating field lines. These measurements are
then compared with modeled spacecraft observations across a localized poloidal
wave resonator in the dayside plasmasphere. A detailed investigation of
theoretically expected poloidal eigenfrequencies allows us to specify the
observed 16 mHz pulsation as a third harmonic oscillation. Based on
this we perform a case study providing a clear identification of wave
properties such as an spatial scale structure of about 0.67 RE, the
azimuthal wave number m≈30, temporal evolution, and energy transport
in the detected ULF pulsations.
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