Satellites sat through four days of alert-level electron radiation after a minor solar storm

Four times in a row, NOAA’s Space Weather Prediction Center posted a notice that electrons above 2 MeV at geostationary orbit were running past its alert line of 1,000 flux units. The first came on Nov. 8 and the last on file at Nov. 11, and the readings climbed each day until the daily peak reached 6,420.

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The trigger was a minor geomagnetic storm that began on Nov. 7, and the radiation-belt surge that followed outlasted it by days. Storms and radiation-belt electrons are related but separate things on the center’s product list, so an electron alert can run on after the geomagnetic index has settled.

From a G1 storm on Nov. 7 to the first electron alert

The center’s alerts feed shows the geomagnetic index reaching 5 at 19:45 UTC on Nov. 7 and again in the 00:00 to 03:00 UTC window on Nov. 8, with the second notice stamped 02:03 UTC. A level of 5 on the Kp scale is a G1, or Minor, storm. NOAA’s space weather scales list the effects as weak power grid fluctuations and possible minor impact on satellite operations, and rate G1 as occurring about 1,700 times per 11-year solar cycle, roughly 900 days.

Electron flux crossed the alert threshold on GOES-19 at 22:45 UTC on Nov. 8, and the alert went out at 23:24 UTC. The feed carried a continuing-alert notice on each of the next three days, at 10:01 UTC on Nov. 9, 05:01 UTC on Nov. 10 and 05:01 UTC on Nov. 11. Counted by calendar date, the alert spanned four days, Nov. 8 through Nov. 11. Elapsed time is shorter, about 54 hours from the 22:45 UTC crossing on Nov. 8 to the 05:01 UTC notice on Nov. 11, which is why the daily-date count and a stopwatch count differ.

Daily peaks of 1,228, 4,674 and 6,420

Each continuing notice quotes the previous day’s maximum. Nov. 8 topped out at 1,228 at 23:35 UTC, barely above the line. Nov. 9 reached 4,674 at 16:30 UTC. Nov. 10 peaked at 6,420 at 15:50 UTC, the highest of the run and about 6.4 times the alert threshold. The Nov. 11 notice at 05:01 UTC was still a continuing alert when this was checked, so the record does not show an end date.

The measurement comes from the GOES satellites, which report 5-minute averages of electrons above 2 MeV at geostationary orbit, according to the center’s GOES electron flux product page. The alert fires when the flux exceeds 1,000 particles per square centimeter per second per steradian. Flux there is usually highest near local noon and lowest near local midnight, so a satellite’s exposure changes through each day. The page adds a caveat that the 2 MeV channel can be contaminated by energetic protons, so the data are not valid during significant proton events, and nothing in the feed for these days flags a proton event.

Deep-dielectric charging and a NASA yardstick

The concern is deep-dielectric charging. The product page explains that energetic electrons penetrate spacecraft components and deposit charge inside the material, and once enough builds up it can discharge as an arc, causing anomalous behavior and temporary or permanent loss of function. The center’s relativistic electron forecast page, which credits the model to Air Force Col. Chris Smithro, says such electrons can cause spacecraft upsets or complete failures, and the forecast model is built to flag damaging events a day to three days ahead. The center issues its alert when the flux stays above 1,000 for more than three consecutive five-minute periods, which screens out brief spikes. The model itself predicts the 24-hour fluence from solar wind speed and performs best near solar minimum, with errors that grow around solar maximum. A companion WMO product page names the satellite industry among the users of the alerts.

A figure from NASA gives the readings some scale. A paper by NASA Marshall Space Flight Center’s J. Minow and colleagues, presented in 2024, set the internal charging launch constraint for the James Webb Space Telescope at 49,800 flux units, measured at a GOES satellite. During that launch the flux topped the 1,000 alert level but peaked about an order of magnitude below the constraint. The 6,420 peak on Nov. 10 sits roughly one-eighth of that value, though the 49,800 figure belongs to one telescope’s design and not to satellites in general.

The alert text carries flux readings and not outage reports, so the record reviewed here does not say whether any spacecraft had trouble. What it documents is exposure: a minor storm, then four dates of alert status, with a daily maximum that rose from 1,228 to 6,420. Whether the flux fell back under 1,000 after the Nov. 11 notice is the open question, and the next continuing-alert message or the product’s own end-of-event notice will settle it, along with how long the exposure lasted in total.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.