Fading Events Research Articles

Observations of travelling ionospheric disturbances using stationary satellites

Observations, at a sub-auroral zone site, of transmissions from certain geo-stationary satellites, have revealed an unusual regular type of fading, apparently due to diffraction from moving ionospheric formations. The velocity of movement of these electron density irregularities was measured by means of a spaced receiver network, which in turn, allowed their height to be computed, in several instances, as well as certain other parameters of interest. The fading is deduced to result from electron density discontinuities, with linear gradients ~700 cm −3 m −1, and located usually near the F-region maximum, which travel in a generally equatorwards direction at ~50–120 m/sec. Apparent periodicity in many fading events, and an association with ionosonde-measured disturbance, suggest that the diffraction takes place at facets of travelling wavelike formations in the ionosphere. Additional observational evidence is presented to support a hypothesis of ducted acoustic-gravity waves, probably excited by impulsive auroralzone events, and having horizontal wavelengths of ~50–100 km, with latitudinal extent, on occasion, exceeding 1500 km.