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Ann. Geophys., 22, 1705-1718, 2004
www.ann-geophys.net/22/1705/2004/
© European Geosciences Union 2004
High-latitude propagation studies using a meridional chain of LF/MF/HF receivers
J. LaBelle
Department of Physics and Astronomy, Dartmouth College, Hanover, New Hampshire, USA
Abstract. For over a decade,
Dartmouth College has operated programmable radio receivers
at multiple high-latitude sites covering the frequency range
100-5000kHz with about a 1-s resolution. Besides detecting
radio emissions of auroral origin, these receivers
record characteristics of the ionospheric propagation of natural and
man-made signals, documenting
well-known effects, such as the diurnal variation in the
propagation characteristics of short and long waves, and also
revealing more subtle effects.
For example, at auroral zone sites in equinoctial
conditions, the amplitudes of distant transmissions on MF/HF frequencies
are often enhanced by a few dB just before they fade away at dawn.
The polarization and/or direction of the arrival of ionospherically
propagating signals in the lower HF range (3-5MHz) show a consistent
variation between pre-midnight, post-midnight, and pre-dawn conditions.
As is well known, magnetic storms and substorms dramatically affect
ionospheric propagation;
data from multiple stations spanning the invariant latitude range
67-79° reveal spatial patterns of propagation
characteristics associated with magnetic storms and substorms.
For example, in the hours preceding many isolated substorms,
favorable propagation conditions occur at progressively lower
latitudes as a function of time preceding the substorm onset.
For some of these effects, explanations follow readily from
elementary ionospheric physics, but understanding others requires
further investigation.
Key words. Magnetospheric physics (annual phenomena) –
Radio science (ionosphere propagation; radio-wave propagation)6
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