Solar Flares & CMEs — The Big Events — Aurora Guide
Solar Flares & CMEs — The Big Events
Not all solar activity is the same. There are three types of events that affect aurora, and they work very differently — which is why a "5-day aurora forecast" is nearly useless, but a "1-hour forecast" is highly reliable.
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Solar wind — always on
The Sun constantly streams charged particles toward Earth at 400–800 km/s. This is what we measure live at L1 (the monitoring station between Earth and the Sun). It takes ~45 minutes to arrive after measurement. Responsible for everyday aurora at high latitudes.
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Solar flare — X-rays in 8 minutes
A sudden burst of X-ray radiation from the Sun. Arrives at Earth in just 8 minutes (travelling at the speed of light). Flares disrupt radio communications and can compress Earth's magnetic field — but the aurora effect alone is modest. The bigger consequence is that large flares often launch a CME.
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CME — the big storm, 1–3 days away
A Coronal Mass Ejection is a billion-tonne cloud of magnetised plasma hurled from the Sun. When it arrives at Earth (1–3 days later), it can trigger Kp 7–9 geomagnetic superstorms — the kind visible from mid-latitudes. The May 2024 event was a CME. When space weather agencies issue a "G3 storm watch," they've spotted a CME en route.
🔭 Why forecasts are hard: We can only detect a CME's strength and magnetic direction when it reaches the L1 monitor — just ~45 minutes before it hits Earth. Until then, every "3-day CME forecast" is an educated guess. When you see a major storm warning, act fast.
Check tonight's aurora forecast