QUASI-PERIODIC SCINTILLATION EVENTS AT SOUTHERN AURORAL LATITUDES

Quasi-periodic (QP) radio scintillations were observed during 1987 on 244 MHz and 1.5 GHz geostationary satellite transmissions in the southern auroral zone from Davis station (68.6-degrees-S, 78.0-degrees-E geographic, 74.6-degrees-S LAMBDA) in Antarctica. Three distinct types of OP events were identified, with occurrence times mainly restricted to the period 18-00 MLT. The substantial loss of signal associated with these events appears to be an important factor in determining the reliability of satellite links on 1.5 GHz in auroral regions. Previous observations at mid-latitudes of QP scintillations have noted a preference for large zenith angles and equatorward azimuths. It is demonstrated that a height transition in a densely ionized layer can produce QP scintillations in a manner analogous to a dense column of ionization but at lower ionization densities, as well as demonstrating a zenith angle and azimuthal dependence that is more consistent with observations than a column of ionization. At the occurrence times noted, the raypath may be intersecting the poleward edge of the trough where sporadic-E is a regular feature. QP scintillation events may result when the E(s)-layer is height modulated by the passage of acoustic-gravity waves originating in the auroral zone.