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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 15, issue 12
Ann. Geophys., 15, 1548–1556, 1997
https://doi.org/10.1007/s00585-997-1548-2
© European Geosciences Union 1997
Ann. Geophys., 15, 1548–1556, 1997
https://doi.org/10.1007/s00585-997-1548-2
© European Geosciences Union 1997

  31 Dec 1997

31 Dec 1997

High-latitude HF Doppler observations of ULF waves. 1. Waves with large spatial scale sizes

D. M. Wright, T. K. Yeoman, and P. J. Chapman D. M. Wright et al.
  • Department of Physics and Astronomy, University of Leicester, University Road, Leicester, LE1 7RH, UK

Abstract. A quantitative study of observations of the ionospheric signatures of magnetospheric ultra low frequency (ULF) waves by a high-latitude (geographic: 69.6°N 19.2°E) high-frequency Doppler sounder has been undertaken. The signatures, which are clearly correlated with pulsations in ground magnetometer data, exhibit periods in the range 100–400 s and have azimuthal wave numbers in the range 3–8. They are interpreted here as local field line resonances. Phase information provided by O- and X-mode Doppler data support the view that these are associated with field line resonances having large azimuthal scale sizes. The relative phases and amplitudes of the signatures in the Doppler and ground magnetometer data are compared with a model for the generation of Doppler signatures from incident ULF waves. The outcome suggests that the dominant mechanism involved in producing the Doppler signature is the vertical component of an E × B bulk motion of the local plasma caused by the electric field perturbation of the ULF wave.

Key words. Auroral ionosphere · Magnetosphere-ionosphere interactions · MHD waves and instabilities HF Doppler · ULF Waves

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