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Ann. Geophys., 25, 1113-1124, 2007
www.ann-geophys.net/25/1113/2007/
© European Geosciences Union 2007
Modulation of radio frequency signals by ULF waves
C. L. Waters1, T. K. Yeoman2, M. D. Sciffer1, P. Ponomarenko1, and D. M. Wright2
1School of Mathematical and Physical Sciences, The University of Newcastle, Callaghan, 2308, New South Wales, Australia
2Department of Physics and Astronomy, University of Leicester, University Road, Leicester, LE1 7RH, UK
Abstract. The ionospheric plasma is continually perturbed by ultra-low frequency (ULF;
1–100 mHz) plasma waves that are incident from the magnetosphere. In this
paper we present a combined experimental and modeling study of the variation
in radio frequency of signals propagating in the ionosphere due to the
interaction of ULF wave energy with the ionospheric plasma. Modeling the
interaction shows that the magnitude of the ULF wave electric field,
e, and the geomagnetic field, B0, giving an e×B0
drift, is the dominant mechanism for changing the radio frequency.
We also show how data from high frequency (HF) Doppler sounders can be
combined with HF radar data to provide details of the spatial structure of
ULF wave energy in the ionosphere. Due to spatial averaging effects, the
spatial structure of ULF waves measured in the ionosphere may be quite
different to that obtained using ground based magnetometer arrays. The ULF
wave spatial structure is shown to be a critical parameter that determines
how ULF wave effects alter the frequency of HF signals propagating through
the ionosphere.
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