Space Weather
Proton Flux — live and explained
High-energy protons from the Sun, monitored continuously by GOES satellites — the basis for NOAA's radiation storm (S-scale) alerts.
Current Proton Flux (≥10 MeV)
Updated every few minutes from live GOES data.
Source: NOAA GOES (integral proton flux, ≥10 MeV)
Why it matters
This is the basis for NOAA's S-scale radiation storm classification, which matters directly for astronaut safety, polar flight routes (where radiation exposure is higher), and satellite electronics, which can be damaged or upset by a strong proton event. It's a genuinely different hazard from geomagnetic storms — it's about radiation exposure, not magnetic disturbance.
Normal range
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.
What today's value means
Waiting for live data to interpret…
What is proton flux?
During large solar flares and coronal mass ejections, the Sun can accelerate protons to extremely high energies. GOES satellites measure how many of these high-energy protons (specifically, ≥10 MeV — energetic enough to penetrate spacecraft shielding) are arriving per second, in units called particle flux units (pfu). Background levels are typically well under 1 pfu; NOAA's radiation storm alert threshold is 10 pfu.
NOAA S-scale (radiation storms)
| Level | Flux threshold | Typical effect |
|---|---|---|
| S0 | < 10 pfu | No radiation storm. |
| S1 | ≥ 10 pfu | Minor — no biological effects. |
| S2 | ≥ 100 pfu | Moderate — minor radiation risk to astronauts on EVA. |
| S3 | ≥ 1,000 pfu | Strong — radiation risk to astronauts, possible satellite issues. |
| S4 | ≥ 10,000 pfu | Severe — significant radiation risk, satellite/HF radio disruption. |
| S5 | ≥ 100,000 pfu | Extreme — high radiation risk, widespread satellite/radio impact. |
FAQ
Is proton flux the same as solar wind density?
No — they're genuinely different measurements. Solar wind density counts the ordinary, low-energy particles that make up the constant solar wind. Proton flux specifically tracks rare, very high-energy protons accelerated by major solar events, which pose a real radiation hazard.
Does proton flux affect aurora?
Not directly — aurora visibility is driven mainly by Kp index, solar wind speed, and Bz. Proton events matter more for radiation exposure and polar radio blackouts than for aurora brightness.