Auroral substorms suddenly brighten and race the lights poleward
Quiet auroral arcs can linger for hours, then a substorm dumps stored magnetic energy in minutes. Curtains brighten, break into rays, and surge toward the magnetic pole in a vivid expansion.
Ground magnetometers and all-sky cameras catch the onset as night-side field lines reconnect in the magnetotail. The show may last tens of minutes before fading back to quieter glow.
Aurora is choreography, not a steady lamp. Substorms are the sudden dance steps that turn a pale arc into a sky-filling storm of green and red.
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