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Ann. Geophys., 24, 1839-1849, 2006
www.ann-geophys.net/24/1839/2006/
© European Geosciences Union 2006
Irregular HF radio propagation on a subauroral path during magnetospheric substorms
D. V. Blagoveshchensky1, T. D. Borisova2, and J. W. MacDougall3
1St. Petersburg State University of Aerospace Instrumentation, St. Petersburg, Russia
2Arctic and Antarctic Research Institute, St. Petersburg, Russia
3University of Western Ontario, London, Ontario, Canada
Abstract. The impact of the main ionospheric trough, sporadic
structures, gradients and inhomogeneities of the subpolar ionosphere during
substorms on the signal amplitude, azimuthal angles of arrival, and
propagation modes for the radio path Ottawa (Canada)-St. Petersburg
(Russia) was considered. This subauroral path with the length of about
6600 km has approximately an east-west orientation. The main goals are to carry
out numerical modeling of radio propagation for the path and to compare the
model calculations with experimental results. Wave absorption and effects of
focusing and divergence of rays were taken into consideration in the radio
wave modeling process. The following basic results were obtained: The signal
amplitude increases by 20–30 dB 1–1.5 h before the substorm expansion
phase onset. At the same time the signal azimuth deviates towards north of
the great circle arc for the propagation path. Compared with quiet periods
there are effects due to irregularities and gradients in the area of the
polar edge of the main ionospheric trough on the passing signals.
Propagation mechanisms also change during substorms. The growth of signal
amplitude before the substorm can be physically explained by both a decrease
of the F2-layer ionization and a growth of the F2-layer height that leads to
a decrease of the signal field divergence and to a drop of the collision
frequency. Ionospheric gradients are also important. This increase of signal
level prior to a substorm could be used for forecasting of space weather
disturbed conditions.
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