Spatial Characteristics of Mid-Latitude Ionospheric Scintillations in VHF Radio-Satellite Transmissions

Simultaneous recordings of VHF radio-satellite transmissions from Transit satellites were obtained at three latitudinally displaced sites in the vicinity of Brisbane (36°S geom.lat): St.Lucia (S), Taringa (T) and Boreen Pt. (B). The meridional displacement were: S-T (2.12 km) and T-B (121.0 km). The location of the site B was such that it was almost directly under a field point MT (i.e. the point at an ionospheric height when the ray-path from a satellite to the site T was tangential to the magnetic field). A number of scintillation patches (so-called the P-type events), showing large enhancement (more than 10 dB) near the local magnetic zenith, were predominantly recorded at the sites S and T whereas the site B showed little or no scintillation activity. The anomalous situation is explained in terms of the geometry between the ray-path and magnetic field, associated with different positions of MT and MB (for the site B). It is suggested that the predominant effect in causing scintillation-producing irregularities becoming invisible from the site B, is associated with an alternative model of scintillation generation based on specular reflection of radio signal.