1. 1 CLUSTER SATELLITE OBSERVATIONS OF FIELD LINE RESONANCES IN THE DAYSIDE MAGNETOSPHERE P. T. I. Eriksson, L. G. Blomberg Alfvén Laboratory, Royal Institute of Technology, Stockholm, Sweden

2. 2 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

3. 3 Background cont.Background

4. 4 Spacecraft orbit Plot in GSM-coordinates Snapshot taken at 16:00 UT

5. 5 Fieldline footprint

6. 6 Electric field

7. 7 Spectral characteristics

8. 8 Data bandpass-filtered 2-10 mHz Background magnetic field defined by 20 min running average r~radial; e~eastward; p~parallell

9. 9

10. 10 Phase relationships

11. 11 Phase relationships cont.

12. 12 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.