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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 25, issue 4
Ann. Geophys., 25, 1011-1024, 2007
https://doi.org/10.5194/angeo-25-1011-2007
© Author(s) 2007. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 25, 1011-1024, 2007
https://doi.org/10.5194/angeo-25-1011-2007
© Author(s) 2007. This work is distributed under
the Creative Commons Attribution 3.0 License.

  08 May 2007

08 May 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 S. Schäfer et al.
  • 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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