A solar storm is a burst of energy and material from the sun that can disrupt technology on Earth, trigger widespread auroras, and in extreme cases knock out power grids. These events originate when tangled magnetic fields on the sun’s surface snap and reconnect, releasing enormous amounts of energy in seconds. That energy can take several forms: a flash of radiation (a solar flare), a rush of high-speed particles, or a massive cloud of electrically charged gas hurled into space (a coronal mass ejection). Sometimes a single event produces all three.
Solar Flares vs. Coronal Mass Ejections
The two main types of solar storms behave very differently. A solar flare is essentially a burst of light spanning the entire electromagnetic spectrum, from radio waves to X-rays and gamma rays. It travels at the speed of light, reaching Earth in about eight minutes. Flares can immediately disrupt radio communications and degrade GPS signals, but they don’t carry physical material.
A coronal mass ejection (CME) is something else entirely. It’s a giant bubble of plasma, millions of miles across, that erupts from the sun’s outer atmosphere and races through space at over a million miles per hour. Despite that speed, a CME typically takes one to three days to reach Earth. When it arrives, it slams into our planet’s magnetic field and can trigger what scientists call a geomagnetic storm. These storms are what cause the most serious effects on the ground.
What Happens When a CME Hits Earth
Earth’s magnetic field normally deflects the solar wind, the constant stream of particles flowing from the sun. But when a powerful CME arrives with its magnetic field oriented opposite to Earth’s, it transfers a surge of energy into the magnetosphere. This energizes electrons already trapped in Earth’s magnetic environment and sends them spiraling down toward the poles at roughly one-tenth the speed of light. When those electrons collide with oxygen and nitrogen atoms in the upper atmosphere, above about 60 miles up, those atoms release the energy as light. That glow is the aurora borealis in the north and aurora australis in the south.
During mild storms, auroras stay confined to high latitudes, places like northern Michigan or Maine. Stronger storms push the auroral oval much farther south. At the most extreme levels, auroras have been spotted from Florida and southern Texas.
How Solar Storms Affect Power Grids
The same geomagnetic disturbance that creates beautiful auroras can wreak havoc on electrical infrastructure. As Earth’s magnetic field fluctuates rapidly during a storm, it induces slow-moving electrical currents in long conductors like power lines and pipelines. These geomagnetically induced currents flow into power transformers and push them outside their normal operating range, saturating their magnetic cores.
Once a transformer’s core saturates, it loses its ability to regulate voltage properly. Currents and voltages in the windings spike to abnormal levels, generating heat that can physically damage the transformer. The distorted electrical signal also confuses protective equipment elsewhere in the grid, tripping circuit breakers that shouldn’t be tripping. That cascading effect pulls critical equipment offline. If the grid is already running near peak demand when a geomagnetic storm hits, the added strain can lead to partial or even system-wide blackouts. In a G5 (extreme) storm, pipeline currents can reach hundreds of amps.
Satellites, GPS, and Radio
Satellites face a different set of problems. Energized particles can build up electrical charge on a spacecraft’s surface, interfering with its electronics, orientation systems, and communication links. Low-orbit satellites also experience increased atmospheric drag because the upper atmosphere heats and expands during a storm, which can alter their orbits unpredictably.
GPS accuracy takes a hit because the signals pass through the ionosphere, which becomes turbulent during geomagnetic storms. During the extreme storm in May 2024, high-accuracy GPS positioning errors exceeded 20 centimeters, a significant problem for precision applications like surveying and autonomous navigation. High-frequency radio communications, used by aviation and emergency services, can go completely dark during severe storms, sometimes for one to two days at a stretch.
The NOAA G-Scale
NOAA rates geomagnetic storms on a five-level scale from G1 (minor) to G5 (extreme), based on the Kp-index, a measure of how disturbed Earth’s magnetic field is on a scale of 0 to 9. Here’s what each level looks like in practical terms:
- G1 (Minor): Weak power grid fluctuations. Aurora visible at high latitudes. Migratory animals may be affected.
- G2 (Moderate): Voltage alarms in high-latitude power systems. Aurora visible as far south as New York and Idaho.
- G3 (Strong): Voltage corrections needed on power grids. Intermittent GPS and radio issues. Aurora visible from Illinois and Oregon.
- G4 (Severe): Widespread voltage control problems. Satellite tracking and orientation disrupted. Aurora visible from Alabama and northern California.
- G5 (Extreme): Possible grid collapse and transformer damage. Satellite operations severely affected. Radio and GPS navigation degraded for hours to days. Aurora visible from Florida and southern Texas.
The Carrington Event: The Worst on Record
The most powerful solar storm in recorded history struck on September 1, 1859. English astronomer Richard Carrington was sketching sunspots through a filtered telescope when he witnessed an intense white flash on the sun’s surface. Seventeen hours later, a massive CME reached Earth, far faster than usual.
The night sky across North America lit up so brightly it looked like daytime. Auroras were visible as far south as Panama. Magnetometers, instruments that measure Earth’s magnetic field, pegged their needles off-scale. Surges of electricity flooded telegraph systems worldwide, shocking operators and making it impossible to send messages. In Florida, where almost no one had ever seen an aurora, people were amazed and frightened. If a Carrington-class event hit today, the consequences for power grids, satellites, and communications would be orders of magnitude more severe simply because modern civilization depends on those systems.
How Much Warning We Get
Solar flare radiation arrives at the speed of light, giving essentially no warning. For CMEs, the picture is slightly better. NASA and NOAA monitor the sun with space-based observatories, and the DSCOVR satellite sits at a gravitational balance point about a million miles from Earth, directly between us and the sun. When a CME passes DSCOVR, it typically provides 15 to 60 minutes of warning before the storm reaches Earth. That’s a narrow window, but it’s enough time for power grid operators to reduce loads and for satellite controllers to put spacecraft into safe mode.
NOAA’s Space Weather Prediction Center also issues forecasts days in advance when sun-watching satellites detect a CME launch. These early forecasts can’t predict the storm’s exact strength, since that depends on the CME’s magnetic orientation, something that can only be measured when it passes DSCOVR. But they give utilities, airlines, and space agencies time to prepare.
Why Solar Storms Are Increasing Right Now
The sun follows an approximately 11-year activity cycle, swinging between quiet periods (solar minimum) and periods of frequent flares and CMEs (solar maximum). We’re currently in Solar Cycle 25, which NOAA’s prediction panel expects to peak around July 2025, though the window stretches from late 2024 through early 2026. The predicted peak sunspot number is around 115, with a range of 105 to 125. During solar maximum, strong geomagnetic storms become significantly more likely, and aurora sightings push to lower latitudes more frequently.
Radiation Risk at High Altitude
At ground level, Earth’s atmosphere and magnetic field shield people from virtually all solar radiation. The risk increases with altitude. Airline passengers and flight crews absorb higher radiation doses during solar storms, particularly on polar routes at cruising altitude where Earth’s magnetic shielding is weakest. Airlines sometimes reroute flights away from the poles during strong solar particle events to reduce crew and passenger exposure. Astronauts face the greatest risk, and space agencies set career radiation dose limits to manage it.