**What a Geomagnetic Storm Does Besides Aurora | Lumavik** > Power grids, satellites, GPS and radio: documented geomagnetic storm effects at each NOAA G level, with the 1989 Quebec blackout and the 2022 Starlink losses. Source: https://lumavik.org/skywatch/geomagnetic-storm-effects/ · updated: 2026-08-07 - [Home](https://lumavik.org/)/ - [Skywatch](https://lumavik.org/skywatch/) # Geomagnetic storm effects: what happens besides aurora Published August 7, 2026 Lumavik editorial Power grids, satellites, GPS and radio: documented geomagnetic storm effects at each NOAA G level, with the 1989 Quebec blackout and the 2022 Starlink losses. Aurora is the visible consequence of a geomagnetic storm. It is not the important one. The same current systems that light the sky induce voltages in power lines, heat the upper atmosphere enough to drag satellites out of orbit, and disturb the ionosphere that satellite navigation depends on. A geomagnetic storm is a sustained disturbance of Earth’s magnetosphere driven by an extended period of energy transfer from the solar wind. This page sets out what those storms are documented to affect, at what severity, with dated examples. ## The mechanism: why a magnetic change becomes an electrical current One process underlies most of the ground-level effects, and it is worth understanding because it explains which infrastructure is vulnerable and which is not. During a storm, currents flowing in the auroral ionosphere at about 100 kilometres altitude change rapidly in strength and position. A changing magnetic field induces an electric field in conducting material beneath it — the same physics as a transformer, on a planetary scale. That electric field drives current through any long grounded conductor: high-voltage transmission lines, pipelines, railway signalling circuits, undersea cables. The result is called a geomagnetically induced current, or GIC. It is quasi-direct, which is the problem. Power grids are engineered for alternating current, and transformers exposed to a direct component can saturate — drawing large reactive currents, heating, generating harmonics, and tripping protective relays that were never designed to interpret this condition. Two factors decide local exposure, and neither is latitude alone. Ground conductivity matters: regions sitting on ancient resistive rock, such as the Canadian Shield or the Scandinavian bedrock, couple more strongly than regions on conductive sedimentary basins. And the length and orientation of the conductor matter, because a longer line accumulates more induced voltage. ## Effects by storm level The table below is NOAA’s own published scale, which pairs each level with documented effects and an average frequency per 11-year solar cycle. | Level | Kp | Power systems | Spacecraft | Radio and navigation | Frequency per cycle | | --- | --- | --- | --- | --- | --- | | G1 Minor | 5 | Weak grid fluctuations | Minor impact on operations | — | ~1700 | | G2 Moderate | 6 | High-latitude voltage alarms; long storms may damage transformers | Corrective orientation action may be needed; drag affects orbit predictions | HF radio can fade at higher latitudes | ~600 | | G3 Strong | 7 | Voltage corrections required; false alarms on protection devices | Surface charging; increased LEO drag | Intermittent satellite navigation and HF problems | ~200 | | G4 Severe | 8, incl. 9− | Widespread voltage control problems; protective systems trip key assets | Surface charging and tracking problems | Satellite navigation degraded for hours; HF sporadic; induced pipeline currents | ~100 | | G5 Extreme | 9 | Widespread voltage and protection problems; some grids may collapse; transformers may be damaged | Extensive surface charging; orientation, uplink and downlink problems | HF may be impossible for 1–2 days; satellite navigation degraded for days | ~4 | *Documented geomagnetic storm effects by NOAA G level, with the agency's published average frequency per 11-year solar cycle. The frequencies are long-run averages across cycles of very different strength, not a schedule. Free to reuse with a link to this page.* ## Power grids: the 1989 case On 13 March 1989 a severe geomagnetic storm caused the Hydro-Québec grid to collapse in about 90 seconds, leaving roughly six million people without power for around nine hours. The sequence is the textbook example of GIC. Induced currents saturated transformer cores; the resulting reactive power demand and harmonic distortion caused protective equipment to trip; the loss of those elements cascaded through a network that had been operating normally seconds earlier. Nothing was struck, nothing overloaded in the conventional sense, and the grid was gone in a minute and a half. Québec was particularly exposed for structural reasons rather than bad luck: high geomagnetic latitude, very long transmission lines carrying power south from remote generation, and the highly resistive rock of the Canadian Shield beneath them. The industry response since has been substantial. Grid operators now receive space-weather warnings, reliability standards address geomagnetic disturbance planning, and operational procedures exist for reducing exposure during a forecast event — running with more reserve margin, deferring maintenance that would take elements out of service, and in some cases reducing transfers on the most exposed corridors. That preparation is the reason a modern G4 event does not reproduce 1989. It is not a reason to treat the risk as solved, and NOAA’s own G5 language still states plainly that some grid systems may experience complete collapse. ## Satellites: charging and drag Spacecraft are affected by geomagnetic storms in two distinct ways, and the second is less intuitive. **Surface charging** builds differential voltages between parts of a spacecraft exposed to different particle environments. When those differences discharge, the resulting transient can corrupt data, upset electronics or damage components. NOAA’s scale describes surface charging from G3 upward, and extensive charging at G5. **Atmospheric drag** is the effect that ends missions. Energy deposited during a storm heats the upper atmosphere, which expands, which raises the air density at any given altitude. A satellite in low Earth orbit that was flying through a certain density is suddenly flying through more of it, and drag rises accordingly. The clearest recent illustration is from February 2022. SpaceX launched 49 Starlink satellites on 3 February into a deliberately low initial orbit, a design choice that lets failed units re-enter quickly. A geomagnetic storm arrived while they were at that altitude, drag rose sharply, and the company reported that up to 40 of the 49 were lost. Drag also degrades orbit prediction generally, which matters for collision avoidance across the whole low-Earth-orbit population — an increasingly crowded environment where a day of poor position knowledge has consequences beyond any single operator. ## Navigation and radio **Satellite navigation** depends on signals traversing the ionosphere, and receivers correct for the delay that imposes. A storm disturbs ionospheric electron content rapidly and unevenly, and the correction models degrade. NOAA describes navigation as degraded for hours at G4 and for days at G5. Consumer navigation usually remains usable — a phone that is a few metres out is still telling you which road you are on. The applications that break first are the ones depending on centimetre-level precision: surveying, offshore positioning, and precision agriculture, where automated guidance can become unusable during a storm that a driver would otherwise not notice. **High-frequency radio** propagates by refracting off the ionosphere, and a disturbed ionosphere absorbs and scatters those signals instead. NOAA’s G5 description states that HF propagation may be impossible in many areas for one to two days. This matters most where HF is the fallback rather than a hobby. Polar aviation routes have poor geostationary satellite coverage, so HF is the practical communication method, and airlines reroute away from polar tracks during significant events. That costs fuel and time; it is an operational and commercial problem rather than a safety emergency. ## Pipelines, railways and other long conductors Pipelines carry cathodic protection systems that hold the metal at a controlled voltage relative to the surrounding soil to prevent corrosion. Induced currents during a storm disturb that control, which can accelerate corrosion and cause spurious readings during inspection. NOAA lists induced pipeline currents affecting preventive measures from G4. Railway signalling and undersea communication cables have shown susceptibility for the same structural reason: they are long, grounded and conductive. Historical accounts of telegraph systems operating without batteries, or shocking operators, during the 1859 Carrington event describe exactly this mechanism at an extreme intensity. ## What geomagnetic storms do not do Several claims circulate during large storms and are not supported. **They are not a health risk on the ground.** Earth’s atmosphere and magnetic field absorb the particle radiation, and surface magnetic variations are orders of magnitude too small to have any biological effect. Elevated radiation exposure is a genuine consideration for astronauts, and a much smaller one for crew on high-altitude polar flights during solar radiation storms, which are rated on a separate NOAA scale. **They do not cause earthquakes or volcanic activity.** There is no mechanism connecting magnetospheric currents to processes kilometres down in the crust. **They do not damage phones, laptops or domestic wiring.** GIC scales with conductor length; a domestic circuit is far too short to accumulate a meaningful induced voltage. The vulnerable infrastructure is measured in hundreds of kilometres. **A solar flare is not a geomagnetic storm.** Flare radiation arrives in about eight minutes and causes radio blackouts on the sunlit side; the geomagnetic storm, if there is one, comes from a coronal mass ejection arriving 15 to 90 hours later. Coverage that conflates the two produces most of the confusion during large events. - [The glossary](https://lumavik.org/skywatch/aurora-glossary/) separates the terms. ## Why this matters for aurora watchers Two practical points connect this to the sky. The first is that infrastructure effects and aurora visibility scale together. NOAA’s scale states the lowest geomagnetic latitudes at which aurora has been reported at each level: about 55 degrees at G2, 50 at G3, 45 at G4 and 40 at G5. If you are at a mid-latitude site, the storms that put aurora over you are the same ones that put grid operators on alert — which is a reasonable way to calibrate how rare your opportunity is. - [What Kp you need where you live](https://lumavik.org/skywatch/what-kp-index-to-see-northern-lights/) covers the thresholds. The second is that the G-scale is a better planning signal for mid-latitude observers than a bare Kp number, precisely because each level carries a documented statement of how far the aurora has historically reached. - [How the geomagnetic indices differ](https://lumavik.org/skywatch/geomagnetic-indices-explained/) sets the scales side by side. ## Bottom line Geomagnetic storms affect infrastructure through geomagnetically induced currents: rapidly changing ionospheric currents induce an electric field in the ground, which drives quasi-direct current through long grounded conductors. Transformers are the vulnerable component because they are not designed for a DC component and can saturate. On 13 March 1989 this collapsed the Hydro-Québec grid in about 90 seconds, cutting power to roughly six million people for around nine hours. Satellites are affected by surface charging and, more consequentially, by increased atmospheric drag as storm heating expands the upper atmosphere — SpaceX reported losing up to 40 of 49 Starlink satellites launched on 3 February 2022 to a storm that arrived while they were at a low initial altitude. Satellite navigation degrades for hours at G4 and days at G5, hitting centimetre-precision users such as surveying and precision agriculture long before consumer navigation. High-frequency radio can be unusable for one to two days at G5, which drives polar flight rerouting. NOAA’s published average frequencies per 11-year cycle are about 1700 G1, 600 G2, 200 G3, 100 G4 and 4 G5 events. Geomagnetic storms pose no health risk on the ground, do not cause seismic activity, and do not damage domestic electronics — the induced voltage scales with conductor length, and the vulnerable systems are hundreds of kilometres long. ## Sources Every figure on this page traces to one of these. All are public and free to read; where a number depends on the data version or the interval examined, we say so rather than printing a single tidy value. - [NOAA Space Weather Scales](https://www.swpc.noaa.gov/noaa-scales-explanation)NOAA SWPC - [Geomagnetic Storms](https://www.swpc.noaa.gov/phenomena/geomagnetic-storms)NOAA SWPC - [Satellite Drag](https://www.swpc.noaa.gov/impacts/satellite-drag)NOAA SWPC - [GOES Magnetometer](https://www.swpc.noaa.gov/products/goes-magnetometer)NOAA SWPC - [Solar and Geophysical Event Reports](https://www.swpc.noaa.gov/products/solar-and-geophysical-event-reports)NOAA SWPC - [North American Electric Reliability Corporation](https://www.nerc.com/)NERC - [Space weather data](https://www.ncei.noaa.gov/products/space-weather)NOAA NCEI - [Space weather](https://www.esa.int/Space_Safety/Space_weather)ESA - [Canadian Space Weather Forecast Centre](https://www.spaceweather.gc.ca/)Natural Resources Canada **Where the numbers come from.** Kp values, the 3-day geomagnetic forecast, the OVATION auroral-oval model and real-time solar wind are published by the NOAA Space Weather Prediction Center in the public domain. Lumavik is not affiliated with NOAA. Forecasts are probabilities: activity, latitude, darkness and cloud all have to cooperate, and cloud cover alone can end the night regardless of everything else. ### Get this as an alert instead of a browser tab Lumavik watches the same NOAA feeds and pushes a notification when the aurora is actually plausible where you are — scored against your geomagnetic latitude and whether it is dark yet, not against a planetary average. - [Get the app](https://lumavik.org/get/) Free · NOAA data · no account ## Frequently asked questions Can a geomagnetic storm knock out the power grid? Yes, and it has. On 13 March 1989 a severe geomagnetic storm collapsed the Hydro-Québec grid in about 90 seconds, leaving roughly six million people without power for around nine hours. The mechanism is geomagnetically induced current: the rapidly changing magnetic field drives a quasi-direct current through long grounded conductors, which saturates transformer cores and can trip protective systems or damage the transformers themselves. NOAA's G5 description states that some grid systems may experience complete collapse. Does a geomagnetic storm affect GPS? Yes. Satellite navigation depends on signals passing through the ionosphere, and a storm disturbs the ionosphere's electron content unpredictably, introducing position errors. NOAA's scale describes satellite navigation as degraded for hours at G3 and for days at G4 and G5. High-precision applications that depend on centimetre-level accuracy — surveying, precision agriculture, some marine operations — are affected long before consumer navigation becomes noticeably wrong. Are aeroplanes affected by geomagnetic storms? Polar routes are. High-frequency radio, which is the communication method available over the poles where satellite coverage is poor, degrades during storms and can be unusable for one to two days at the highest levels. Radiation exposure at cruising altitude also rises during solar radiation storms, which are rated on a separate NOAA scale. The operational response is rerouting away from polar tracks, which costs fuel and time rather than creating a safety emergency. Can a solar storm damage satellites? It can, through several mechanisms. Surface charging can build differential voltages that discharge and damage components. Increased atmospheric heating expands the upper atmosphere and raises drag on low-Earth-orbit satellites, changing their orbits and shortening their lifetime. In February 2022 SpaceX reported that up to 40 of the 49 Starlink satellites launched on 3 February were lost after a geomagnetic storm increased drag at their initial low deployment altitude. Is a geomagnetic storm dangerous to people on the ground? No. Earth's atmosphere and magnetic field absorb the particle radiation, and the magnetic field variations at the surface are far too small to affect the human body. The risks from geomagnetic storms are to technological infrastructure, not to health. Elevated radiation exposure is a genuine consideration for astronauts and, to a much smaller degree, for crew on high-latitude flights at high altitude during solar radiation storms. How often do damaging geomagnetic storms happen? NOAA publishes average frequencies per 11-year solar cycle: about 1700 G1 events, 600 G2, 200 G3, 100 G4 and 4 G5. The levels where infrastructure effects become serious are G4 and G5, so roughly 100 severe and 4 extreme events per cycle. These are long-run averages across cycles of very different strength, and the observed distribution in any single cycle can differ considerably. ## Keep reading - [Free tool **Geomagnetic Latitude Calculator and Kp Thresholds**](https://lumavik.org/tools/geomagnetic-latitude-calculator/) - [Skywatch **Solar Cycle 25 and the aurora: a dated timeline**](https://lumavik.org/skywatch/solar-cycle-25-and-the-aurora/) - [Skywatch **Kp index explained, and what it cannot tell you**](https://lumavik.org/skywatch/kp-index-explained/) - [Skywatch **Geomagnetic indices explained, side by side**](https://lumavik.org/skywatch/geomagnetic-indices-explained/) - [Free tool **Live aurora forecast: current Kp and the NOAA 3-day outlook**](https://lumavik.org/tools/aurora-forecast/) - [Skywatch **Solar Wind Aurora Forecast: Read Bz, Speed and Density**](https://lumavik.org/skywatch/solar-wind-and-aurora/) - [Skywatch **Geomagnetic latitude aurora: why your neighbour sees more aurora**](https://lumavik.org/skywatch/geomagnetic-latitude-and-aurora/) - [Skywatch **Aurora glossary: the space-weather terms defined**](https://lumavik.org/skywatch/aurora-glossary/) --- HTML version: https://lumavik.org/skywatch/geomagnetic-storm-effects/ Structured data for this site: https://lumavik.org/api/v1/openapi.json · https://lumavik.org/llms.txt Free to quote and reuse with a link back to the source URL above (CC BY 4.0).