Characteristic types of ionospheric scintillations at VHF for a typical mid-latitude station over a sunspot cycle (1988–1996)

Abstract

Abstract A 9-year study (1988–1996) of ionospheric scintillations, occurring during the last sunspot cycle, was undertaken at a typical southern mid-latitude station, Brisbane (invariant latitude 35.6°S). Scintillations in the VHF radio-satellite beacon transmissions, using the polar-orbit Transit satellites, were recorded for 13 000 passes. Unlike the previous studies careful attention was given to the spatial morphology of scintillation events at various phases of the solar cycle. It is now evident that scintillation-causing small-scale (kilometric) irregularities are distinctly different in their origin during sunspot maximum and minimum. The so-called S-type scintillations, characteristic of sunspot maximum, are caused by irregularities associated with the equatorward edge of the auroral scintillation oval which expands well into mid-latitudes during high solar activity. This type is almost completely absent at sunspot minimum when truly mid-latitude scintillations (so-called P-type) are formed as patches North of the station, close to the local magnetic zenith. A few cases were available when both scintillations and mid-latitude range spread-F occurred simultaneously. From this and from the general morphology of mid-latitude spread-F it can be inferred that the same type of irregularities is responsible for both phenomena.