A solar storm begins at the sun’s surface and, over the course of hours to days, sends a wave of charged particles and magnetic energy toward Earth. When that wave arrives, it compresses Earth’s magnetic field, drives electrical currents through the ground, disrupts satellite signals, and lights up the sky with auroras visible far beyond the polar regions. The full sequence involves several distinct phases, each with different effects on the planet and on the technology we depend on.
How a Solar Storm Starts
The sun’s surface is threaded with powerful magnetic field lines that can twist, tangle, and suddenly snap. When they do, two things can happen, sometimes simultaneously. A solar flare releases a burst of electromagnetic radiation (X-rays, ultraviolet light, radio waves) that travels at the speed of light and reaches Earth in about eight minutes. A coronal mass ejection, or CME, launches billions of tons of superheated plasma into space. That cloud of magnetized material is slower, traveling at roughly 600 miles per second or more, and typically arrives at Earth one to three days later.
Flares and CMEs are related but separate events. A flare is a flash of energy. A CME is a physical eruption of solar material. Either can occur without the other, though the most intense solar storms involve both. The flare acts as a warning shot: it can cause brief radio blackouts on the sunlit side of Earth within minutes. The CME is the main event, carrying the magnetic punch that triggers a full geomagnetic storm.
What Happens When the Plasma Hits Earth
Earth’s magnetic field normally acts as a shield, deflecting the constant stream of particles flowing from the sun. A CME overwhelms that shield through a process called magnetic reconnection. When the CME’s magnetic field lines are oriented opposite to Earth’s, the two fields merge at the boundary of the magnetosphere. This opens gaps that allow solar wind energy, mass, and momentum to pour across the barrier and flood into the space around Earth.
Once inside, the solar wind drags magnetic field lines over the polar caps and stretches them far behind Earth into a long magnetic tail. Energy builds up in that tail until it snaps back, releasing energized particles that spiral along field lines toward the poles. These particles slam into the upper atmosphere and create the visible effects we see from the ground, while also pumping electrical energy into the entire system. The stronger the CME and the more favorable its magnetic orientation, the more severe the resulting geomagnetic storm.
Auroras and Their Colors
The most spectacular visible result of a solar storm is the aurora. Energized particles funnel down along Earth’s magnetic field lines and collide with gas molecules in the upper atmosphere. The color of the aurora depends on which gas gets hit and at what altitude.
- Green: Oxygen between 75 and 110 miles up. This is the most common aurora color.
- Red: Oxygen above 120 miles, where the atmosphere is thinner and collisions are less frequent.
- Blue: Nitrogen between 75 and 110 miles.
- Pink: Nitrogen below 60 miles, where particles penetrate deeper into the atmosphere.
- Purple and white: Combinations of oxygen and nitrogen emissions blending together.
During minor storms, auroras stay close to the Arctic and Antarctic. During powerful storms, the oval of aurora expands toward the equator, and people in the mid-latitudes (or even the subtropics, in extreme cases) can see the lights. The famous 1859 Carrington Event produced auroras visible as far south as the Caribbean.
Effects on the Power Grid
The rapid changes in Earth’s magnetic field during a geomagnetic storm induce electrical currents in any long conductor on the ground, including power transmission lines, pipelines, and undersea cables. These are called geomagnetically induced currents, or GICs, and they pose the biggest infrastructure risk of any solar storm.
GICs flow into high-voltage power transformers and push their magnetic cores beyond normal operating limits, a condition called saturation. Once saturated, the transformer loses its ability to regulate current and voltage. Windings carry abnormally large currents, and surrounding metal structures heat up from induced eddy currents. Depending on the transformer’s design and age, this can cause permanent damage. Replacing a large power transformer takes months, which is why a severe storm affecting many transformers at once is considered one of the most serious space weather scenarios. The 1989 geomagnetic storm knocked out power across the entire province of Quebec in about 90 seconds.
GPS and Satellite Disruption
Solar storms alter the density of the ionosphere, the electrically charged layer of the atmosphere that GPS and communication signals pass through. Irregular pockets of electron density scatter radio waves in a phenomenon called scintillation. Under severe scintillation conditions, a GPS receiver can lose lock on the satellite signal entirely, making it impossible to calculate a position. Less extreme conditions degrade accuracy and reduce confidence in location data. Low-frequency navigation signals used by aviation can also be disrupted for brief intervals.
Satellites in low Earth orbit face a separate problem. The heated, expanded atmosphere increases drag on spacecraft, pulling them into lower orbits faster than expected. Operators have to use onboard fuel to correct for the extra drag, shortening the satellite’s useful life. In February 2022, a geomagnetic storm caused SpaceX to lose 38 newly launched Starlink satellites that couldn’t climb to their target orbits through the unexpectedly dense upper atmosphere.
High-energy particles from solar storms also penetrate spacecraft electronics, causing glitches in onboard computers, degrading solar panels, and potentially blinding camera sensors on Earth-observation satellites.
Radiation Risks for Astronauts and Aircrew
On the ground, Earth’s atmosphere and magnetic field absorb virtually all of the dangerous radiation from a solar storm. In space, the situation is very different. Solar particle events release fast-moving protons that can penetrate spacecraft shielding. Animal studies using simulated solar particle radiation show that even relatively low doses can increase blood clotting times and cause nausea. At higher doses, the effects worsen significantly. Astronauts aboard the International Space Station shelter in the most shielded sections of the station during major events, and future crews traveling to the Moon or Mars will face even greater exposure because they’ll be farther from Earth’s protective magnetic field.
Airline crews and passengers on high-latitude, high-altitude routes also receive elevated radiation doses during solar particle events, though the amounts are far smaller than in space. Airlines sometimes reroute polar flights during strong storms to reduce exposure and maintain reliable radio contact.
How Strong Can Solar Storms Get
Solar storms vary enormously in intensity. The strongest confirmed event in recorded history is the 1859 Carrington Event, which drove magnetic field measurements off the scale at observatories and induced currents strong enough to shock telegraph operators and set telegraph paper on fire. The Halloween storms of 2003 were powerful enough to damage a transformer in South Africa and force the rerouting of airline flights, but they were still estimated to be significantly weaker than the Carrington Event.
Solar storms follow roughly 11-year cycles of activity. The current cycle, Solar Cycle 25, is expected to reach its peak around July 2025, though the actual maximum could fall anywhere between late 2024 and early 2026, with a predicted sunspot count of 105 to 125. During solar maximum, the frequency of CMEs and intense flares increases substantially, making strong geomagnetic storms more likely. Solar Cycle 26 is expected to begin sometime between 2029 and 2032, but no predictions for its strength exist yet.
The practical concern for most people is not the average storm but the rare extreme event. A Carrington-scale storm today could cause widespread, long-lasting power outages, GPS blackouts, and satellite failures. Space weather forecasting from NOAA’s Space Weather Prediction Center provides warnings ranging from hours to days before a CME arrives, giving grid operators and satellite controllers time to take protective action, though the most precise predictions of a storm’s severity only become possible about 15 to 45 minutes before impact, when the CME passes monitoring spacecraft stationed between Earth and the sun.