On the origin of dusk radar scatter events

Abstract

The possibility of the generation of decameter scale ionospheric plasma density irregularities, that must be responsible for dusk scatter, by the plasma gradient drift instability (GDI) at F-region altitudes is considered. It is shown that the dusk scatter could be produced by the ion density perturbations which appear as a result of the development of the GDI produced by the maximum westward plasma drift in the region poleward of the trough minimum. Possible reasons for the appearance of growth of the GDI waves as a result of the development of the trough plasma GDI during or just after sunset in the F-region are discussed. It is shown that, if the GDI begins after sunset, then the influence of the drift velocity shear results in the action of the GDI during 1–2 hours after sunset, which is close to the duration of dusk scatter.