CLUSTER SATELLITE OBSERVATIONS OF FIELD LINE RESONANCES IN THE DAYSIDE MAGNETOSPHERE

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CLUSTER SATELLITE OBSERVATIONS OF FIELDLINE
RESONANCES IN THE DAYSIDEMAGNETOSPHERE
P. T. I. Eriksson, L. G. Blomberg
Alfvén Laboratory, Royal Institute of Technology,
Stockholm, Sweden
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Background
Assume wave propagation on the form
The hydrodynamic equations in a cylindrical
geometry then gives
Two limit cases
Toroidal and poloidal mode resp.
In general (finite m) the two modes are coupled
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Background cont.
Background
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Spacecraft orbit

• Plot in GSM-coordinates
• Snapshot taken at 1600 UT

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Fieldline footprint
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Electric field
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Spectral characteristics
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• Data bandpass-filtered 2-10 mHz
• Background magnetic field defined by
• 20 min running average
• rradial eeastward pparallell

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Phase relationships
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Phase relationships cont.
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Summary of observations

• On 17 August 2002 a FLR event is observed in the
  dayside magnetosphere.

• The oscillations occur at one stable frequency,
  4.2 mHz
• in the satellite frame.

• Radial polarisation of the magnetic field
  indicates the
• poloidal mode.