Space Weather 101
☢️ Proton Flux
View live Proton Flux data →What is Proton Flux?
Proton flux measures how many high-energy protons (specifically ≥10 MeV, energetic enough to penetrate spacecraft shielding) are arriving from the Sun, in particle flux units (pfu). Large flares and CMEs can accelerate protons to these energies, and a proton event typically follows a major flare by tens of minutes to a few hours.
Why it matters
Proton flux is the basis for NOAA's S-scale radiation storm classification, which matters directly for astronaut safety, polar flight routes (where radiation exposure from space is naturally higher), and satellite electronics, which can be damaged or temporarily disrupted by a strong proton event.
Typical values
Background levels are typically well under 1 pfu. NOAA's radiation storm alert threshold is 10 pfu (S1). Major events can reach into the thousands or, rarely, hundreds of thousands of pfu (S4-S5) during the most extreme solar radiation storms on record.
How scientists measure it
GOES satellites carry dedicated high-energy particle detectors that continuously count incoming protons above several energy thresholds, reporting the results as integral flux (particles above a given energy) in real time.
Why it affects Earth
Proton events are a genuinely different hazard from geomagnetic storms — they're about radiation exposure, not magnetic disturbance. They pose an elevated radiation risk to people in high-altitude polar flights and astronauts, and can degrade or upset satellite electronics.
FAQ
Is proton flux the same as solar wind density?
No — solar wind density counts the ordinary, low-energy particles making up the constant solar wind. Proton flux specifically tracks rare, very high-energy protons from major solar events, a genuinely different measurement and hazard.