Every aurora is ultimately powered by the Sun. The Sun constantly sheds the solar wind, and embedded in it are the magnetic disturbances that energize the aurora. When the solar wind arrives faster, denser, or with a southward-pointing magnetic field, it couples more strongly to Earth’s magnetosphere and the lights intensify.
The biggest displays usually follow explosive events. Solar flares are sudden bursts of radiation from the Sun’s surface, often near sunspots — cooler, magnetically intense regions. Flares frequently come with coronal mass ejections, enormous clouds of magnetized plasma. If a CME is aimed at Earth, it can take one to three days to arrive and then trigger a geomagnetic storm, the kind of event that drives Kp to storm levels and pushes the aurora far from the poles.
Solar activity rises and falls on a roughly 11-year solar cycle. Around solar maximum, sunspots, flares and CMEs are most frequent, so storms — and far-reaching auroras — happen more often. Near solar minimum the Sun is calmer and big displays are rarer, though fast solar-wind streams can still spark activity.
This is why aurora forecasting is part astronomy, part weather. Space-weather centers watch the Sun for flares and CMEs, then watch the incoming solar wind to judge how strong the response at Earth will be — a chain that turns events on a star 150 million km away into a glow over your horizon.