Auroral spirals, 1. Observations

Abstract

Auroral spirals of 20- to 1300-km diameter are a common part of the active auroral display. They appear most frequently in the evening and midnight sectors, where they appear to be produced as a consequence of magnetic field line distortion caused by field-aligned currents. More quiescent spiral forms exhibiting somewhat different characteristics occur during quiet times in the polar cap near the dawn portion of the auroral oval. (AIP)