Radiation

Solar storms and your flight: what actually changes at 35,000 feet

September 13, 2026Updated October 20, 202610 min readFor pilots and passengers

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In this article

Two kinds of radiation at cruise
Three NOAA scales, three different problems
An S-level is not a dose rate
Ground level enhancements are the rare big ones
January 2026: the strongest radiation storm in over 20 years
ICAO space weather advisories
What airlines do in practice
What LogAloft does with this

Most of the radiation dose on a flight at cruise comes from galactic cosmic rays, and that part is lowest near solar maximum, not highest. Solar storms add dose only occasionally, mostly at high latitudes and high altitudes, and only the rare, very energetic events push dose rates far above the normal background.

Two kinds of radiation at cruise

Galactic cosmic rays (GCR) come from outside the solar system. NOAA's Space Weather Prediction Center (SWPC) describes their spectrum as varying only slowly with time, a background that reaches the atmosphere all the time. Earth's magnetic field deflects many of them away from the equator but gives little protection above roughly 55 degrees magnetic latitude. The FAA puts the background effective dose rate at FL370 at very high latitudes at about 8 µSv/h, falling to roughly a quarter of that near the equator (FAA InFO 20007).

The Sun changes GCR on an 11-year rhythm. Near solar maximum, the solar wind and its magnetic field keep a larger share of lower-energy cosmic rays from reaching Earth. Near solar minimum they get in more easily, so GCR peaks near solar minimum (NOAA SWPC). This slow cycle touches every flight, every month. The table shows its size in LogAloft's calculations for a great-circle flight at FL350 with step climbs and the same air time, with only the solar conditions changed:

Route (LogAloft calculation)	October 2009 (solar minimum)	January 2026 (near solar maximum)	Change
JFK–LHR	about 41 µSv	about 24 µSv	about 40% lower
JFK–NRT	about 89 µSv	about 52 µSv	about 40% lower

January 2026 was a month of high solar activity. Activity also changes from month to month, and by July 2026 the same JFK–LHR flight was back up to about 30 µSv, the figure in our route table.

Solar cosmic radiation is the second source. The FAA describes a solar particle event as a temporary increase that is usually very small compared with the GCR background but on rare occasions can be much larger. It can last from a few minutes to more than a day, and it is greatest near the magnetic poles, dropping off quickly toward the geomagnetic equator (FAA AC 120-61B).

Three NOAA scales, three different problems

NOAA rates space weather on three scales.

The S-scale, for solar radiation storms, is based on protons of 10 MeV and above measured by GOES satellites in geostationary orbit. S1 starts at 10 particle flux units, and each step is ten times higher, up to S5 at 100,000. NOAA expects about 50 S1 storms in an 11-year cycle, 3 at S4 and fewer than one at S5. From S2 up, NOAA's impact text says passengers and crew in high-flying aircraft at high latitudes may be exposed to radiation risk. HF radio through the polar regions suffers at every level, from minor effects at S1 to possible blackouts at S4 and S5.

The G-scale, for geomagnetic storms, is based on the Kp index. These storms are caused mainly by coronal mass ejections (CMEs) striking Earth's magnetic field, and their aviation effects fall mostly on communication and navigation. At G4, NOAA lists sporadic HF propagation and satellite navigation degraded for hours. At G5, HF may be impossible in many areas for one to two days, and satellite navigation may be degraded for days. NOAA expects about 100 G4 storms and 4 G5 storms per cycle.

The R-scale, for radio blackouts, is driven by X-rays from flares. NOAA lists effects on HF radio and low-frequency navigation signals on the sunlit side of the Earth, lasting minutes to hours. Radio blackouts bring no added radiation for aircraft.

A geomagnetic storm can still matter for radiation. In a 2023 paper, researchers from NOAA and the FAA note that when the field is disturbed, the boundary between open and closed magnetic field lines can shift several degrees toward the equator, exposing lower latitudes to higher dose rates. They single out routes between the continental US and Europe, which run close to that boundary, and say dose rate uncertainty there can range from a factor of two to an order of magnitude or more, depending on how disturbed the field is (Bain et al., Space Weather, 2023).

An S-level is not a dose rate

The S-scale counts protons of 10 MeV and above in space. What raises dose at cruise is the far more energetic end of the spectrum, protons of roughly 500 MeV to several GeV. The same NOAA paper looks at S1 and S2 events in January 2005: they carried few protons above 100 MeV, produced no rise at ground-based neutron monitors and would not have required an ICAO radiation advisory. As the authors put it, not every proton event is energetic enough to alter the radiation environment at flight levels.

Ground level enhancements are the rare big ones

A ground level enhancement (GLE) is a solar particle event energetic enough to raise the count rates of neutron monitors on the ground. The GLE database at the University of Oulu registers one when at least two differently located monitors, including one near sea level, record near-simultaneous, statistically significant increases, matched by a rise in proton flux measured in space. Only 73 GLEs were registered from 1942 to 2023 (Poluianov et al., Solar Physics, 2025).

Solar cycle 25 has produced five so far, all listed in the Oulu database:

GLE	Date	Notes
73	28 October 2021	First GLE of cycle 25 (Papaioannou et al., 2022)
74	11 May 2024	Peak increase about 10% at the Dome C monitor in Antarctica, during a G5 storm (Papaioannou et al., 2025)
75	8 June 2024	Missed in real time and identified later in neutron monitor data (Poluianov et al., 2025)
76	21 November 2024	Listed in the Oulu database
77	11 November 2025	Strongest GLE since 1989 by integral intensity, fourth strongest of the neutron-monitor era (Mishev et al., 2026)

GLE 77 is the event that matters most for aviation this cycle. GLEs 73 to 76 were weak, with GLE 74 the strongest of them. For GLE 77, an Oulu-led data summary estimated an effective dose rate of about 75 µSv/h at 35,000 feet in the polar region, above ICAO's moderate threshold and close to the severe one (Mishev et al., 2026). A separate August 2026 study reports that it raised aviation dose rates above 30 µSv/h, about four times the typical GCR rate (Lei, Dyer and Ryden, JSWSC, 2026).

For scale, the same study says the February 1956 GLE, the strongest on record, drove dose rates up by three orders of magnitude, and it estimates the event dose on a polar flight at 40,000 feet at about 4.7 mSv. Modeling of GLE 69 in January 2005 found the ICAO severe threshold exceeded down to FL320 over the polar and mid-latitude bands at the event's onset, with advisories running for about 6.5 hours (Bain et al., 2023).

January 2026: the strongest radiation storm in over 20 years

On 19 January 2026, SWPC reported that GOES-19 measurements showed an S4 (Severe) solar radiation storm, a level not observed since October 2003. SWPC said the effects were mainly restricted to polar aviation routes and polar HF communication, and that it had notified airlines and the FAA, among others. CNN's headline quoted forecasters calling it the largest solar radiation storm "in over 20 years" (CNN).

The CME behind it left the Sun on 18 January with an R3 flare (SWPC), and G4 (Severe) geomagnetic storm levels were reached at 1938 UTC on 19 January after the CME arrived (SWPC).

What the record does not show: as of early October 2026, the Oulu database lists no GLE for January 2026, and GLE 77 remains the most recent. A severe S-level in space is not the same as a GLE-level dose at cruise. We found no published measurement of aircraft dose rates during this storm, so we don't give one.

ICAO space weather advisories

Since 7 November 2019, global space weather centers have issued advisories to aviation under ICAO Annex 3 and the guidance in ICAO Doc 10100 (FAA InFO 20007). There are now four global centers, rotating duty every two weeks: SWPC (US), ACFJ (Australia, Canada, France, Japan), PECASUS (a European consortium led by Finland) and CRC (China and Russia, operating since December 2020). South Africa's SANSA is a regional center (ICAO APAC, 2025; PECASUS).

Advisories cover HF COM, GNSS and RADIATION, each at MOD (moderate) or SEV (severe). The main thresholds:

Advisory	MOD	SEV
RADIATION (effective dose rate)	30 µSv/h, issued FL250 to FL460	80 µSv/h, issued at any level above FL250
HF COM, auroral absorption	Kp 8	Kp 9
HF COM, shortwave fadeout	X1 flare	X10 flare
GNSS, amplitude scintillation (S4 index)	0.5	0.8

The FAA InFO also lists thresholds for polar cap absorption and other GNSS effects. It notes that an advisory is not a SIGMET and that its coarse 30-degree latitude bands can overstate the affected airspace.

Radiation advisories have been rare. ICAO's management report on the service's 2024 performance, dated June 2025, says six RAD advisories were issued in error on 24 March 2024 and that, apart from tests, no valid RAD advisory had been issued since operations began in 2019. We did not find an official count of advisories for GLE 77 or for January 2026.

What airlines do in practice

For US carriers, polar operations need FAA authorization, and the operator's operations specifications must contain a plan for mitigating crew exposure to radiation during solar flare activity (14 CFR Part 121, Appendix P). The FAA's advisory circular says flying lower can significantly reduce exposure in high-latitude areas, particularly if the response is quick (AC 120-61B).

Rerouting has real costs. A 2025 comment in npj Space Exploration reports that during the October 2003 storms, several New York to Hong Kong flights were diverted, burning an extra 26,600 pounds of fuel and giving up more than 16,500 pounds of payload. It lists lower altitudes, different routings and delayed departures as the usual options (Xue, 2025). Which of these applies on a given day is set by each airline's procedures and the published guidance, and those are what pilots should follow.

What LogAloft does with this

The LogAloft home page shows current space weather. Each flight's dose uses that month's solar conditions, taken from the FAA's monthly data or, for recent months, a neutron-monitor nowcast, so the solar-cycle effect described above is built into your numbers. On Pro, the dose comes from the track the aircraft actually flew; free accounts get that for flights between US airports, from the FAA's data, within the plan's limits. Otherwise the dose is an estimate along the route an airline would plan for that day's winds. For doses on 14 common routes, see How much radiation do you get on a flight?

Storms are left out of the routine dose. Turn on Count solar and geomagnetic storms in Settings, and a flight that met a solar radiation storm (from NASA's NAIRAS model) or a geomagnetic storm (Kp 5 or higher) shows the extra dose on its own line, kept apart from the routine GCR estimate. For a geomagnetic storm, LogAloft follows the CARI-7A method and lowers the magnetic cutoff by the same fixed factor whenever Kp is 5 or higher. In LogAloft's calculations at FL350, that raises the dose rate by about 46% to 69% near the equator, depending on solar activity (about 59% on average under July 2026 conditions), although the rate there starts low, so the extra is about 1 µSv an hour. At 45°N it ranges from about 1% over North America to about 30% over East Asia (about 22% over Europe). From 55°N it is under 10%, and over North America it is next to nothing.

Sources

This is information, not medical advice. For questions about your own health or a pregnancy, talk to your doctor or aviation medical examiner.