The highest daily peak in NOAA’s current run of electron alerts was 3,304 pfu, logged at 11:05 UTC on October 26 by the 2 MeV channel of a GOES spacecraft. The Space Weather Prediction Center has issued an electron alert on each of seven straight days, from October 24 through October 30, because the flux keeps clearing its 1,000 pfu trigger. The daily maxima it reported ran from 3,169 down to 1,228.
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Nothing in these alerts describes a flare, an aurora or a radio blackout. The product tracks one narrow thing: how many fast electrons cross a detector at geostationary altitude, the ring about 22,000 miles above the equator where weather and communications satellites sit.
Seven alerts, seven daily maxima
Every alert in NOAA’s public alert feed is a continuation notice that reports the previous day’s peak. The October 24 alert, issued at 09:04 UTC as serial 3756, reported 3,169 pfu from October 23. The October 25 alert gave 3,259 pfu for October 24, the October 26 alert gave 2,864 for October 25, and the October 27 alert, sent at 11:38 UTC, gave the run’s high of 3,304 for October 26. After that the numbers fell and rebounded: 1,789 on October 27, 2,493 on October 28 and 1,228 on October 29.
The latest notice went out at 14:59 UTC on October 30 as serial 3762. Its 1,228 pfu is the lowest daily maximum of the seven, yet it still sits 228 pfu above the line that triggers an alert, so the continuation status held. Whether a notice appears on October 31 depends on a number that was not yet published when this was written.
The clock times attached to each maximum are as informative as the values. The October 23 peak came at 15:40 UTC, October 24 at 15:30, October 25 at 18:20, October 26 at 11:05, October 27 at 17:15, October 28 at 18:05 and October 29 at 16:30. Six of the seven fall between mid-afternoon and early evening UTC, and the October 26 maximum, the largest, is the outlier that arrived in the morning hours. A week of nearly daily repeats looks less like a single burst and more like a radiation belt that stayed full for days.
Deep-dielectric charging inside a spacecraft
SWPC’s own page on energetic electrons and satellites lays out why a threshold exists at all. Electrons at these energies can pass through the outer skin of a satellite and lodge inside insulating materials. Charge accumulates there, and when it gets high enough it releases as an arc. SWPC says that discharge can cause anomalous spacecraft behavior and the temporary or permanent loss of functionality.
The trigger itself is spelled out on the GOES electron flux product page: an Electron Event alert is issued when the flux of electrons above 2 MeV exceeds 1,000 particles per square centimeter per second per steradian, the unit that the alert text abbreviates as pfu. A reading of 3,304 is therefore a little over three times the trigger, which is the only yardstick the alerts supply. Every one of the seven daily maxima cleared it, the smallest by 228 pfu and the largest by 2,304.
The feed names no operator and no satellite that misbehaved this week.
What one detector can and cannot say
The measurement behind each alert is a five-minute average from a single instrument family, and SWPC publishes the numbers as machine-readable files in its GOES JSON directory. A daily maximum picks the single highest of those averages. A day reported at 3,304 pfu may have spent most of its hours far lower, and a day reported at 1,228 may have crossed the trigger only briefly, so the series describes peaks and says little about how long a satellite sat in the elevated flux.
Position matters as well. SWPC notes that flux is usually highest near local noon and lowest near local midnight at the spacecraft, which explains why a peak can land at 11:05 UTC one day and 18:20 UTC the day before. The agency also warns that the 2 MeV channel can be contaminated by energetic protons, so the data are not valid during a significant proton event. The agency does not say whether the proton channel was affected on any of these days.
Electron alerts are one product in a wider catalog that SWPC lists on its alerts, watches and warnings page, and the electron notices carry the least drama of any of them. The serial numbers run in unbroken sequence from 3756 on October 24 to 3762 on October 30, so no daily notice was skipped during the week, and the first of them already described a day at 3,169 pfu, well before the run’s peak. They contain no forecast of when the flux will fall, only a record of what the detector saw the day before. The open question for satellite operators is the one the October 30 notice cannot answer: whether 1,228 pfu marks the end of this episode or a pause before another climb above 3,000.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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