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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

)3(1

)2(1

)1(1

2

2

2

22

2

0

2

2

0

2

r

uimBrE

ri

BBirE

BrrB

rm

r

ur

r

BbB

bBBBB

bBBB

)exp( tiim

The hydrodynamic equations in a cylindrical geometry then gives

Two limit cases: mm ;0 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 16:00 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•r~radial; e~eastward; p~parallell

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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 mHzin the satellite frame.

•Radial polarisation of the magnetic field indicates thepoloidal mode.