Recent results in auroral-zone scintillation studies

Nighttime data from the Defense Nuclear Agency's Wideband satellite have consistently shown a pronounced scintillation enhancement at the point where the propagation vector lies within the local L-shell. Simultaneous observations at two well-separated stations and spaced-receiver measurements have shown that this feature is caused by a latitudinally narrow, unstable F-region ionization enhancement that produces sheet-like intermediate-scale structures. A more detailed characterization of the source region has been derived from simultaneous measurements from the TRIAD satellite and the Chatanika radar.The source region is typically convecting southward, whereby the poleward gradient at its southern boundary is stable to the gradient-drift instability. Thus, Ossakow and Chaturvedi (1979) postulated the current-convective instability as a source mechanism. Birkeland currents, when sufficiently intense, can destabilize a region that is otherwise stable to the gradient-drift instability.The sheet-like anisotropy of the irregularities is perhaps the most intriguing feature of the instability. Two mechanisms have been postulated to explain it. This paper reviews the development and current status of our understanding of this recently discovered high-latitude instability.