Solar Energetic Particles (SEPs)
Definition
High-energy protons and ions accelerated by flares and CME shocks, arriving at Earth within minutes to hours.
In plain language
The Sun's biggest eruptions fire particle bullets at near-light speed. They cause radiation storms — polar radio blackouts and aviation rerouting — and can reach Earth long before the CME itself.
The science
SEPs are accelerated by flare reconnection and CME-driven shocks to MeV–GeV energies, guided along IMF field lines. Events are rated on NOAA's S-scale; strong events precede CME arrival by many hours.
Why it matters for aurora viewing
An SEP event is a loud herald: the associated CME often follows within days, frequently bringing a major aurora display behind it.
See this in action on tonight's data.