Recent studies of the structure and morphology of auroral zoneFregion irregularities

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.