Some characteristics of high-latitude substorms

The occurrence characteristics of substorms appearing at invariant latitudes greater than 790 and the movement of associated ionospheric electrojets are investigated. These substorms appear mainly in the winter months during the descending phase of the sun-spot cycle. The substorms generally are localized and occur on days of moderate magnetic activity. The diurnal variation of their occurrence reflects the proximity of the station to the poleward edge of the auroral bulge in the midnight-dawn sector. A study of several selected events suggests that electrojets may occur simultaneously at the equatorward and poleward edges of the auroral oval. (author)