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Ann. Geophys., 22, 169-182, 2004
www.ann-geophys.net/22/169/2004/
© European Geosciences Union 2004
High resolution observations of spectral width features associatedwith ULF wave signatures in artificial HF radar backscatter
D. M. Wright1, T. K. Yeoman1, L. J. Baddeley1, J. A. Davies1,2, R. S. Dhillon1, M. Lester1, S. E. Milan1, and E. E. Woodfield1,3
1Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK
2now at: Space Science and Technology Dept., Rutherford Appleton Laboratory, Chilton, Didcot, Oxon,OX11 0QX, UK
3now at: National Center for Atmospheric Research/High Altitude Observatory, P.O. Box 3000, Boulder, Colorado, 80307-3000, USA
Abstract. The EISCAT high power heating facility at Tromsø, northern Norway, has been
utilised to generate artificial radar backscatter in the fields of view of the CUTLASS
HF radars. It has been demonstrated that this technique offers a means of making
very accurate and high resolution observations of naturally occurring ULF waves.
During such experiments, the usually narrow radar spectral widths associated with
artificial irregularities increase at times when small scale-sized (high m-number)
ULF waves are observed. Possible mechanisms by which these particle-driven high-m waves
may modify the observed spectral widths have been investigated. The
results are found to be consistent with Pc1 (ion-cyclotron) wave activity, causing
aliasing of the radar spectra, in agreement with previous modelling work. The
observations also support recent suggestions that Pc1 waves may be modulated by
the action of longer period ULF standing waves, which are simultaneously detected
on the magnetospheric field lines. Drifting ring current protons with energies of
∼ 10keV are indicated as a common plasma source population for both wave types.
Key words. Magnetospheric physics (MHD waves and instabilities)
– Space plasma physics (wave-particle interactions)
– Ionosphere (active experiments)
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