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Ann. Geophys., 16, 1190-1199, 1998
www.ann-geophys.net/16/1190/1998/
© European Geosciences Union 1998
A comparison of EISCAT and HF Doppler observations of a ULF wave
D. M. Wright, T. K. Yeoman, and J. A. Davies
Department of Physics and Astronomy, University of Leicester, University Road, Leicester, LE1 7RH, UK. e-mail: dmw7@ion.le.uk
Abstract. Since the middle of 1995, an HF Doppler
sounder has been running almost continuously in northern Norway, with the
receiver at Ramfjordmoen and the transmitter at Seljelvnes. Concurrent operation
of the EISCAT UHF radar in common programme (CP-1) mode has made it possible to
study the ionospheric signature of a magnetospheric ULF wave. These are the
first results of such wave signatures observed simultaneously in both
instruments. It has been demonstrated that the observed Doppler signature was
mainly due to the vertical bulk motion of the ionosphere caused by the electric
field perturbation of the ULF wave and the first direct observational
confirmation of a numerical simulation has been achieved. The wave, which was
Alfvénic in nature, was detected by the instruments 8° equatorward of the
broad resonance region. The implications for the deduced wave modes in the
ionosphere and the mechanism producing the HF Doppler variations are discussed.
Key words. Magnetosphere-ionosphere interactions · MHD
waves and instabilities · Radio science · Ionospheric physics
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