Flows in polar cap ionosphere could trigger auroral substorms

Auroral substorms, in which aurorae dramatically brighten and become highly dynamic, occur often and seem to be triggered by electric currents in the ionosphere at high latitude. However, scientists do not know the details of how auroral substorms begin and what drives their expansion and controls their duration. Plasma flows within the ionosphere's polar cap region had not generally been considered to be a driver of auroral substorms, but some recent studies have suggested that mesoscale plasma flows from the polar cap could cross the polar cap boundary and contribute to triggering of flows that may bring new plasma earthward and lead to the onset of substorms.