Loading…
PUBLISHED MODELS, CITED MEASUREMENTS
Français English
DATA STATUS
417 series loaded · last import on 2026-10-25

Radiation belts Satellite-killer electrons, and the solar wind that makes them

The Van Allen belts in cross-section

The Van Allen belts in cross-section Meridian cross-section of the Earth and its dipole magnetic field: field lines, inner proton belt between 1.2 and 2.5 Earth radii, outer electron belt between 3 and 7 Earth radii, GPS and geostationary orbits. GPS Geostationary Inner Outer ← towards the Sun
  • Inner belt: 10–100 MeV protons, stable
  • Outer belt: relativistic electrons, highly variable
  • Dipole field lines (L = 1.5 to 8)
To scale in a dipole field (1 Earth radius = 6,371 km); the real field is compressed on the dayside by the solar wind and stretched into a tail on the nightside. Trapped particles spiral along the field lines, bounce between the hemispheres and drift around the Earth. Between the belts, the “slot region” is emptied by plasma waves. Geostationary satellites (telecommunications, weather) sit in the outer belt; GPS satellites cross it. Orbits are shown by their radius in the equatorial plane (blue dots).
Electrons ≥ 2 MeV now (GOES)
2,314 pfu
2026-10-25 17:45:00 UTC
above the NOAA alert threshold (1,000 pfu)
GOES primary integral electron flux ≥ 2 MeV (NOAA SWPC) · U.S. Government work, public domain · 10/25/26 Current · provisional
Alert days, 1994–2020
25 %
9,458 days measured from 1994 to 2020; mean fluence ≥ 1,000 pfu
Solar wind → electrons delay (days)
2
strongest correlation at +2 days; see the correspondence
Flux of electrons ≥ 2 MeV at geostationary orbit, last 7 days (pfu) GOES primary integral electron flux ≥ 2 MeV (NOAA SWPC) · U.S. Government work, public domain · 10/25/26 Current · provisional
Show the data as a table
Integral flux of electrons of at least 2 MeV measured every 5 minutes by the primary GOES satellite (SEISS instrument), logarithmic scale; 1 pfu = 1 electron per cm², per second and per steradian. The daily cycle comes from the orbit: each day the satellite moves from the dayside (compressed field, high flux) to the nightside. Above 1,000 pfu NOAA issues an alert: the electrons penetrate shielding and charge the internal insulators of satellites until they discharge.
Daily fluence of electrons > 2 MeV, 1994–2020 Daily Particle Data archive, GOES proton and electron fluences 1994–2020 (NOAA SWPC) · U.S. Government work, public domain; credit NOAA SWPC · 10/25/26 Frozen archive
Show the data as a table
Number of electrons above 2 MeV received in a day per cm² and per steradian at geostationary orbit (GOES-7 to GOES-15, NOAA “Daily Particle Data” archive), logarithmic scale. The alert threshold (8.64 × 10⁷, i.e. 1,000 pfu averaged over the day) is crossed mostly during the declining phase of solar cycles, when coronal holes blow a fast, recurrent wind (2003, 2005–2008, 2016–2017). Satellite changes are not intercalibrated.

Share of alert days per year

YearAlert days / measured daysShare
1994 180 / 355 51 %
1995 134 / 324 41 %
1996 81 / 354 23 %
1997 60 / 365 16 %
1998 68 / 365 19 %
1999 53 / 365 15 %
2000 38 / 366 10 %
2001 12 / 365 3 %
2002 16 / 365 4 %
2003 141 / 329 43 %
2004 116 / 366 32 %
2005 148 / 365 41 %
2006 108 / 365 30 %
2007 148 / 365 41 %
2008 155 / 366 42 %
2009 5 / 365 1 %
2010 66 / 365 18 %
2011 66 / 365 18 %
2012 80 / 366 22 %
2013 70 / 365 19 %
2014 14 / 364 4 %
2015 85 / 364 23 %
2016 139 / 366 38 %
2017 159 / 364 44 %
2018 109 / 365 30 %
2019 92 / 365 25 %
2020 8 / 64 12 %
Years with at least 60 measured days. Deep solar minima (2009) and maxima (2000–2002, 2014) are quiet; declining phases, rich in fast wind, are the most disturbed. This is the reverse of intense geomagnetic storms, which are more frequent around the maximum.
Method and sources

Real time: integral flux of electrons ≥ 2 MeV from the primary GOES satellite, 5-minute values (NOAA SWPC, not validated), accumulated import after import. Archive: daily fluence of electrons > 2 MeV and protons > 10 MeV from the NOAA “Daily Particle Data” files, 1994 to March 2020 (GOES-7 to GOES-15). An alert day is a day whose fluence reaches 8.64 × 10⁷ electrons per cm² per steradian, a mean flux of 1,000 pfu, the NOAA alert threshold. The diagram uses a centred dipole: r = L cos² λ.

Reading these data
The detectors changed six times in 26 years (GOES-7 to GOES-15, then GOES-16 with a different instrument): differences of a factor of 2–3 between satellites rule out reading a long-term trend; day-to-day variations are reliable. The flux also depends on the longitude of the satellite. “Killer” electrons have been blamed for satellite failures such as Anik E1 and E2 in January 1994 (Lam et al., 2012).
SOURCES OF THIS PAGE
GOES primary integral electron flux ≥ 2 MeV (NOAA SWPC)
NOAA SWPC, GOES primary satellite SEISS MPS-HI integral electron flux ≥ 2 MeV, 5-minute values. · source page ↗
Licence : U.S. Government work, public domain · retrieved on Oct 25, 2026 · SHA-256 54e8a1b04a3b…
Daily Particle Data archive, GOES proton and electron fluences 1994–2020 (NOAA SWPC)
NOAA SWPC, Daily Particle Data (DPD), GOES-7 to GOES-15 integral particle fluences, old_indices archive. · source page ↗
Licence : U.S. Government work, public domain; credit NOAA SWPC · retrieved on Oct 25, 2026 · SHA-256 7d8ba231a162…

© 2026 Observatoire des phénomènes naturels · About · Data sources · Manage cookies Model results and published measurements, each with its source. The Observatory’s own calculations, correspondences and forecasts, are published with their method and score.