A characteristic sequence of activity when a quiescent aurora suddenly intensifies. In the growth phase, the auroral oval brightens, and in the following expansion phase the activity spreads both eastwards and westwards. Growth towards the pole produces a wavy structure, which moves westwards from the midnight sector as a westward-travelling surge, while the morning sector of the auroral oval breaks up. The display fades away in the final recovery phase.
Subjects: Meteorology and Climatology.