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Simultaneous observations of the polar-orbiting Wideband satellite at two auroral zone stations (separated by approximately 200 km along the geomagnetic meridian) were made during November 1977. The latitudinal distribution of the average scintillation occurrence at each station shows a local maximum at the point where the propagation vector lies within an L shell. This supports the hypothesis that the enhancement is a geometrical effect due to L shell aligned, sheetlike irregularities. The detailed structure of the average scintillation occurrence as well as the scintillation patterns on individual passes shows, however, that the source regions are confined in latitude. From a detailed analysis of total electron content data we were able to show that the local scintillation enhancements occur in a region of enhanced F region ionization with a steep gradient at its equatorward edge. The source region lies within the general confines of the diffuse aurora, often with too limited a latitudinal extent to cause an enhancement at both stations. These new results are discussed in light of recent theoretical analysis by Ossakow and Chaturvedi that shows that the current convective instability, which is essentially a stable E x B configuration destabilized by moderate field-aligned currents, can explain the irregularities. The sheetlike structure is a result of the nonlinear saturation of the instability. The linearly unstable mode, which would give rise to meridional structures, is nonlinearly damped while the dominant nonlinearity favors the perpendicular modes that cause the sheetlike structures.

Recent analyses of auroral‐zone spaced‐receiver measurements have shown that the regions where sheetlike irregularities occur are confined to the equatorward portion of the nighttime scintillation zone where the westward and eastward electrojets flow. Poleward of this region, the irregularities are rodlike. For satellites in highly eccentric orbits, the spaced‐receiver technique can be used to measure ionospheric drifts. Simultaneous incoherent‐scatter radar measurements have revealed two types of F region ionization enhancements that are believed to be the source regions of persistent scintillation features on polar satellite transmissions. One type is found at the equatorward edge of the diffuse aurora and can persist for more than 10 hours. More dynamic structures often occur in pairs, which suggests an association with ‘inverted‐V’ precipitation events. Radar data have also revealed large‐scale east‐west structure in the poleward enhancements.

The time structure of a representative set of weakly and strongly scintillating transionospheric beacon signals is analyzed. Under conditions of weak scatter, the coherence time of the signal intensity is a monotonic function of the Fresnel radius divided by the effective scan velocity. The shape of the function, however, is controlled by the power law index. Data from a Peruvian station show evidence of a slightly steeper spectral distribution than do data from Kwajalein in the Marshall Islands. Under conditions of strong scattering, the intensity coherence time depends only on the perturbation strength. The strong scatter data show remarkably little dispersion when they are plotted against the perturbation strength. The data are all consistent with a phase spectral slope somewhat less than 3, which is independently verified by using phase scintillation data.