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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 24, issue 10
Ann. Geophys., 24, 2719–2733, 2006
https://doi.org/10.5194/angeo-24-2719-2006
© Author(s) 2006. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 24, 2719–2733, 2006
https://doi.org/10.5194/angeo-24-2719-2006
© Author(s) 2006. This work is distributed under
the Creative Commons Attribution 3.0 License.

  20 Oct 2006

20 Oct 2006

Evidence of standing waves during a Pi2 pulsation event observed on Cluster

A. B. Collier1,2, A. R. W. Hughes1, L. G. Blomberg2, and P. R. Sutcliffe3 A. B. Collier et al.
  • 1School of Physics, University of KwaZulu-Natal, Durban, South Africa
  • 2Dept. of Space and Plasma Physics, School of Electrical Engineering, Royal Institute of Technology, Stockholm, Sweden
  • 3Hermanus Magnetic Observatory, Hermanus, South Africa

Abstract. Observations of Pi2 pulsations at middle and low latitudes have been explained in terms of cavity mode resonances, whereas transients associated with field-aligned currents appear to be responsible for the high latitude Pi2 signature.

Data from Cluster are used to study a Pi2 event observed at 18:09 UTC on 21 January 2003, when three of the satellites were within the plasmasphere (L=4.7, 4.5 and 4.6) while the fourth was on the plasmapause or in the plasmatrough (L=6.6). Simultaneous pulsations at ground observatories and the injection of particles at geosynchronous orbit corroborate the occurrence of a substorm.

Evidence of a cavity mode resonance is established by considering the phase relationship between the orthogonal electric and magnetic field components associated with radial and field-aligned standing waves. The relative phase between satellites located on either side of the geomagnetic equator indicates that the field-aligned oscillation is an odd harmonic. Finite azimuthal Poynting flux suggests that the cavity is effectively open ended and the azimuthal wave number is estimated as m~13.5.

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