Solar weather refers to the constant stream of energy, charged particles, and magnetic fields flowing outward from the Sun, along with the dramatic eruptions that periodically intensify that stream. It shapes conditions across the entire solar system, from the auroras shimmering over polar skies to GPS errors that knock farm equipment offline. The Sun’s behavior follows a roughly 11-year cycle of rising and falling activity, and during its peaks, eruptions can unleash enough energy in minutes to dwarf anything human civilization has ever produced. Understanding solar weather has become increasingly urgent as modern life grows more dependent on the satellites, power grids, and communication networks that sit squarely in its path.
What Generates Solar Weather
The Sun is not a static ball of fire. It is a churning mass of electrically conducting plasma, and the interplay between that plasma’s convective motions and the Sun’s rotation generates powerful magnetic fields through a process called the solar dynamo. These fields rise, tangle, and occasionally snap, driving everything from the steady solar wind to the most violent explosions in the solar system. Global simulations of this dynamo process have shown that the magnetic cycle period is tied to how strongly rotation influences the turbulent convection inside a star, a relationship that holds not just for the Sun but for other Sun-like stars as well.
1PubMed. Reconciling solar and stellar magnetic cycles with nonlinear dynamo simulationsThe Sun’s activity rises and falls over roughly 11 years, counted by the number of sunspots visible on its surface. Sunspots are regions where intense magnetic fields break through the photosphere. At solar maximum, the surface is dotted with these dark patches, and the frequency of flares and eruptions climbs sharply. At solar minimum, the Sun quiets down. Predictions for Solar Cycle 25, the current cycle, suggested it would be stronger than the relatively weak Cycle 24, with a peak sunspot number around 154.
2Monthly Notices of the Royal Astronomical Society. Prediction of solar cycle 25: a non-linear approachFlares, Coronal Mass Ejections, and the Solar Wind
Solar weather arrives at Earth in three main forms, each with different speeds and consequences. The first is the solar flare, a sudden burst of electromagnetic radiation released when stressed magnetic field lines reconnect. Flares travel at the speed of light, reaching Earth in about eight minutes. Observations have confirmed that magnetic reconnection is the dominant energy release mechanism in flares, with plasma outflows clocked at roughly 125 kilometers per second at the reconnection site.
3The Astrophysical Journal Letters. Imaging and Spectroscopic Observations of Magnetic Reconnection and Chromospheric Evaporation in a Solar FlareThe second, and typically more consequential for Earth, is the coronal mass ejection. A CME is a massive bubble of magnetized plasma launched from the Sun’s corona into interplanetary space. These structures travel as twisted magnetic flux ropes, expanding nearly linearly as they move outward from the Sun while their internal magnetic field strength declines with distance.
4PubMed Central. Forward Modeling of Coronal Mass Ejection Flux Ropes in the Inner Heliosphere with 3DCORECMEs are slower than light, taking anywhere from 15 hours to several days to cross the Sun-Earth gap, depending on their speed. The fastest ones, associated with the most powerful flares, compress and sweep up the ambient solar wind ahead of them, creating a shock wave that amplifies their punch when they arrive. During flares that produce CMEs, the main energy release and acceleration of high-energy protons begin just as the reconnection rate peaks, after a major shift in the magnetic topology of the eruption.
5Astronomy & Astrophysics. Coupling between magnetic reconnection, energy release, and particle acceleration in the X17.2 2003 October 28 solar flareThe third form is the steady solar wind itself. Even when the Sun is quiet, it continuously emits a stream of charged particles flowing at hundreds of kilometers per second. Coronal holes, regions where the Sun’s magnetic field opens outward, produce especially fast streams. When a fast stream overtakes slower wind ahead of it, the collision creates a compressed region that co-rotates with the Sun and can persist for many solar rotations, producing recurring geomagnetic disturbances at Earth even without any flare or CME.
6PubMed Central. Solar wind stream interaction regions throughout the heliosphereHow Solar Storms Trigger Geomagnetic Disturbances
Earth’s magnetic field acts as a shield against most incoming solar material. Under normal conditions, the solar wind flows around the magnetosphere like water around a stone. Trouble starts when a CME or a fast solar wind stream arrives carrying a magnetic field that points southward, opposite to Earth’s northward-pointing field at the boundary. When those opposing fields meet, they reconnect, opening a channel that funnels energy and particles deep into the magnetosphere. An analysis of every intense geomagnetic storm during Solar Cycle 23 found that all of them occurred when the interplanetary magnetic field was directed southward for extended periods.
7Journal of Geophysical Research: Space Physics. Interplanetary conditions causing intense geomagnetic storms (Dst ≤ −100 nT) during solar cycle 23 (1996–2006)This means the severity of a geomagnetic storm depends not just on how fast or dense the incoming solar material is, but on the direction of its embedded magnetic field. A massive CME aimed directly at Earth can produce only a minor disturbance if its magnetic field happens to point northward, because it reinforces rather than opposes the magnetosphere. Conversely, a moderate CME with a strongly southward field can trigger a significant storm. Forecasters cannot reliably measure that magnetic orientation until the CME is very close to Earth, which is one reason storm severity remains difficult to predict far in advance.
Auroras and What They Reveal
The most visible consequence of solar weather is the aurora. When energy pours into the magnetosphere during a geomagnetic storm, charged particles are accelerated along magnetic field lines toward the polar regions, where they collide with atoms and molecules in the upper atmosphere. Oxygen atoms produce the familiar green and red curtains; nitrogen contributes blues and purples. The diffuse aurora, the broad glow that covers large areas, is driven by electrons and protons scattered by waves in the magnetosphere, while the sharper, more dynamic curtains of discrete aurora result from electrons accelerated by electric fields aligned along the magnetic field.
8Reviews of Geophysics. Mechanisms for auroral precipitation: A reviewProtons contribute their own component. When incoming protons undergo charge-exchange interactions in the atmosphere, they produce neutral hydrogen atoms in excited states that emit characteristic hydrogen spectral lines detectable from the ground.
9Reviews of Geophysics. Auroral proton precipitation and hydrogen emissionsDuring powerful storms, the auroral oval expands dramatically toward the equator. People in the central United States, southern Europe, and even Mexico have reported seeing auroras during the most intense recent events. These displays are beautiful, but they signal that enormous amounts of energy are being dumped into Earth’s upper atmosphere, with practical consequences far beyond the light show.
GPS Errors and Communication Disruptions
The particles and energy deposited in the upper atmosphere during solar storms disturb the ionosphere, the electrically charged layer that GPS signals must pass through. When the ionosphere becomes irregular, GPS signals can flicker in strength (a phenomenon called scintillation) or arrive with warped timing, producing position errors that range from annoying to dangerous. During the St. Patrick’s Day storm of 2015, strong amplitude scintillation caused power fades up to 12 decibels and outright losses of GPS signal lock in the L2 frequency band at high latitudes.
10Journal of Geophysical Research: Space Physics. GPS Scintillations and Losses of Signal Lock at High Latitudes During the 2015 St. Patrick’s Day StormThe May 2024 superstorm showed that mid-latitude regions are vulnerable too. GPS position errors reached up to 70 meters in the central United States during the storm’s main phase, coinciding with reported outages of GPS-guided farming equipment. In the southwestern United States, errors of 10 to 20 meters were linked to storm-enhanced plasma densities, and on the following day, energetic particle precipitation during substorms caused rapidly evolving errors of up to 10 meters.
11Journal of Geophysical Research: Space Physics. Spatio‐Temporal Evolution of Mid‐Latitude GPS Scintillation and Position Errors During the May 2024 Solar StormFor most people, a 70-meter GPS error is a minor inconvenience. But precision agriculture relies on centimeter-level accuracy to plant, spray, and harvest fields. Aviation uses GPS for approach and landing procedures. Offshore drilling platforms depend on precise positioning. When solar weather knocks GPS accuracy from centimeters to tens of meters, entire operations grind to a halt.
Power Grids and Geomagnetically Induced Currents
Rapid fluctuations in Earth’s magnetic field during a storm induce electric fields at the planet’s surface, which drive currents through any long conducting structure. Pipelines, undersea cables, and railroad tracks all pick up these geomagnetically induced currents, but the most consequential targets are high-voltage power transformers. When direct current flows through a transformer designed for alternating current, it pushes the transformer’s magnetic core into saturation on one half of the AC cycle, distorting the waveform and generating excess heat and reactive power consumption.
During the May 2024 storm, two 220-kilovolt transformers experienced multiple bursts of geomagnetically induced current exceeding 50 amps each, peaking at 113 amps. As those currents rose above 30 amps, the transformers’ reactive power consumption increased in step, consistent with half-cycle core saturation.
12Space Weather. Geomagnetically Induced Currents, Transformer Harmonics, and Reactive Power Impacts of the Gannon Storm in May 2024Reactive power is a behind-the-scenes quantity that grid operators must carefully balance. When many transformers across a region simultaneously start consuming extra reactive power, voltage can sag and protection systems can trip, cascading toward blackouts. The most famous example remains the 1989 storm that knocked out the Hydro-Québec grid in 90 seconds, leaving millions without power. Modern grids are somewhat better instrumented, but the fundamental vulnerability remains: long transmission lines in regions with resistive bedrock, like the Canadian Shield or Scandinavia, are especially prone to high induced currents.
Satellite Orbits and Spacecraft Safety
Solar storms heat the upper atmosphere, causing it to expand. At altitudes where low-Earth-orbit satellites fly, typically between 200 and 2,000 kilometers, the thicker atmosphere increases drag, pulling satellites lower faster than expected. During strong storms, this effect intensifies orbit-prediction errors and accelerates orbital decay.
13Space Weather. Estimating Satellite Orbital Drag During Historical Magnetic SuperstormsSpaceX learned this the hard way in February 2022, when a moderate geomagnetic storm struck shortly after a batch of Starlink satellites had been deployed at a low initial orbit. The atmosphere swelled enough that the newly launched satellites could not climb to their operational altitude; most of the batch reentered and burned up. The loss was embarrassing but not dangerous, since the satellites were small and designed to fully disintegrate. For larger assets, especially crewed spacecraft and space stations, the concern is less about reentry and more about collision avoidance. When atmospheric drag shifts every object’s predicted position, the catalogs that track orbital debris become temporarily less reliable, raising the risk of close approaches.
The May 2024 storm also reshaped Earth’s radiation belts, creating a new long-lasting component of relativistic electrons and altering particle fluxes in the South Atlantic Anomaly, a region where the radiation belts dip closest to Earth’s surface.
14Geophysical Research Letters. Effects of the May 2024 Solar Storm on the Earth’s Radiation Belts Observed by CALET on the International Space StationRadiation at Aviation Altitudes
Commercial aircraft cruising at 10 to 12 kilometers fly above most of the atmosphere’s protective blanket. During solar energetic particle events, the flux of high-energy protons reaching these altitudes increases, especially on polar routes where Earth’s magnetic shielding is weakest. Airline crew members who fly polar routes regularly accumulate measurable radiation doses over their careers, and extreme events can spike those doses significantly in a single flight.
15Journal of Geophysical Research: Space Physics. Enhanced Radiation Exposure of Airline Crew and Passengers During the May 2024 Geomagnetic StormSome airlines reroute flights away from polar paths during major solar particle events, adding fuel costs and travel time but reducing crew and passenger exposure. The decision is judgment-based; there is no universally enforced threshold that automatically triggers rerouting. Radiation monitors on some aircraft provide real-time readings, but coverage is far from universal.
The May 2024 Superstorm as a Modern Test Case
The geomagnetic storm of May 10-11, 2024 was the most intense since 2003 and served as a wake-up call for how solar weather affects modern infrastructure. Multiple CMEs arrived at Earth in rapid succession, driving a severe storm that pushed auroras to latitudes where they are almost never seen. Observers in Mexico documented the aurora, and instrument networks across that country recorded solar radio bursts, ionospheric disturbances, and geomagnetically induced currents at three strategic substations of the national electrical system.
16Space Weather. The Mother’s Day Geomagnetic Storm on 10 May 2024: Aurora Observations and Low Latitude Space Weather Effects in MexicoThe storm provided the first major real-world validation of many space-weather models that had been developed during the relatively quiet period since 2003. It confirmed that GPS disruptions extend well into mid-latitudes, that transformer currents in the hundreds of amps are plausible even outside the highest-risk zones, and that satellite radiation environments can change in lasting ways. It also demonstrated how much public awareness of solar weather has grown: social media flooded with aurora photos from places that normally never see them, generating a wave of curiosity about the Sun’s influence on daily life.
The Carrington Event and How Bad It Could Get
The benchmark for a worst-case scenario has long been the Carrington Event of 1859, the most intense geomagnetic storm in the observational record. Telegraph systems worldwide failed, with some operators reporting sparks and fires. In 1859, electrical infrastructure was primitive. A storm of that magnitude today could cause widespread power outages lasting weeks in regions with vulnerable grid designs, damage satellites, and disrupt communications globally.
Interestingly, recent ice-core research has challenged one assumption about Carrington. Analysis of chlorine-36 concentrations in Greenland and Antarctic ice cores found no significant spike around 1859, suggesting that the solar energetic particle event associated with the Carrington storm was either far smaller than previously assumed, at most three times larger than any space-age particle event, or that the particle burst may not have been directed at Earth at all.
17Philosophical Transactions of the Royal Society A. 36Cl Concentrations from Polar Ice Cores Set New Constraints on the Carrington EventThat finding matters because risk models have sometimes treated the Carrington Event as a single catastrophic package: an enormous flare, a fast CME, and a devastating particle storm all in one. The ice-core evidence suggests the particle component may have been modest, meaning the geomagnetic storm (caused by the CME’s magnetic field) was the real threat, not the radiation dose from energetic particles. Separating those two hazards helps refine what a worst-case modern event would actually look like.
Tree rings and ice cores have also revealed that events far more powerful than Carrington have struck Earth over the past several thousand years. Prominent spikes in cosmogenic isotope concentrations found in precisely dated natural archives show that extreme solar particle events have occurred repeatedly over the past 15 millennia.
18arXiv. Linking Solar Magnetism, Extreme Solar Particle Events and Stellar SuperflaresForecasting Solar Weather
Space-weather forecasting has improved considerably but remains far behind terrestrial weather prediction. Agencies like NOAA’s Space Weather Prediction Center monitor the Sun continuously using ground-based observatories and spacecraft positioned at the L1 point, roughly 1.5 million kilometers sunward of Earth. From that vantage, instruments can measure the solar wind about 15 to 60 minutes before it arrives at Earth. That narrow window is a serious limitation for a grid operator who needs hours of lead time to take protective action.
A proposed mission concept called SWIFT aims to place additional spacecraft at the L1 point and closer to the Sun to provide continuous, distributed observations of heliospheric structures, with the goal of improving current forecasting lead times by up to 35 percent.
19Acta Astronautica. Space Weather Investigation Frontier (SWIFT) mission concept: Continuous, distributed observations of heliospheric structures from the vantage points of Sun-Earth L1 and sub-L1Even 35 percent more warning time would translate to only minutes of additional lead, since the baseline is already short. The fundamental problem is that CMEs take one to three days to reach Earth, but their magnetic field orientation, the single most important factor in storm severity, cannot be measured until they arrive. Predicting that orientation from observations at the Sun remains an unsolved problem. Forecasters can say a CME is coming, estimate its arrival time within a window of several hours, and give a probability range for storm intensity, but they cannot say with confidence whether the field will be pointed in the direction that triggers a severe storm until it is practically at our doorstep.
How Birds Respond to Geomagnetic Storms
Solar weather does not affect only technology. Many migratory birds navigate using Earth’s magnetic field, and geomagnetic storms scramble the signal they rely on. A controlled experiment exposing three songbird species to simulated geomagnetic storm conditions found that the European robin reduced its nocturnal migratory restlessness in response, essentially choosing to wait out the disturbance rather than fly with an unreliable compass.
20PubMed Central. Magnetic storms disrupt nocturnal migratory activity in songbirdsA much larger study using weather radar data to track bird migration across the United States found a 9 to 17 percent decrease in migration intensity during severe space-weather events, after accounting for atmospheric weather and other patterns. During fall migration, birds also showed reduced effort flying against the wind under geomagnetic disturbance, suggesting that disrupted magnetic navigation caused them to drift more passively with the wind. The effect was strongest when overcast skies coincided with magnetic disturbance, hinting that birds rely on multiple navigational cues and suffer most when both celestial and magnetic signals are degraded at the same time.
21PubMed Central. Space weather disrupts nocturnal bird migrationWhether this matters for bird populations overall is still unclear. A single night of reduced migration is unlikely to cause lasting harm, but if storms coincide with narrow windows when birds need to reach breeding or feeding grounds, the cumulative effect could matter, especially for species already under pressure from habitat loss.
Solar Weather and Deep Space Exploration
For astronauts venturing beyond low Earth orbit, solar energetic particles become a direct health threat. Earth’s magnetosphere and thick atmosphere absorb most of this radiation for people on the ground, but crews heading to the Moon or Mars lack that protection. Modeling of five solar events in 2012 showed that for the largest of those events, lunar missions would require aluminum shielding between 1.0 and 5.0 grams per square centimeter to keep radiation exposure below the 30-day limits for the lens of the eye and the skin.
22Journal of Space Weather and Space Climate. Modeling the effectiveness of shielding in the earth-moon-mars radiation environment using PREDICCS: five solar events in 2012Mars-bound crews face an even harder version of the problem. A trip to Mars takes six to nine months, during which astronauts are exposed to both the steady drizzle of galactic cosmic rays and any solar particle events that happen to erupt. Without reliable forecasting of when and how severe those events will be, mission designers must build enough shielding and storm shelters into spacecraft to handle a plausible worst case, adding mass and cost.
Stellar Weather and Planetary Habitability
Solar weather is not unique to our Sun. Every star with a magnetic field produces its own version, and for planets orbiting other stars, the consequences can be far more dramatic. M-dwarf stars, the most common type in our galaxy, are often much more magnetically active than the Sun, producing frequent and powerful flares that bombard any orbiting planets with high-energy radiation.
23PubMed Central. The effect of a strong stellar flare on the atmospheric chemistry of an earth-like planet orbiting an M dwarfRecent modeling of the AU Microscopii system, a young M star with known planets, found that stellar flares could accelerate the total atmospheric loss process for habitable-zone planets by a few billion years. For planets at greater orbital distances, flare-driven radiation may be the deciding factor in whether a primordial atmosphere survives at all, since the star’s baseline emissions alone would not be strong enough to strip it away.
24The Astrophysical Journal. The Impact of Stellar Flares on the Atmospheric Escape of Exoplanets Orbiting M Stars. I. Insights from the AU Mic SystemThis research reframes solar weather from a local inconvenience into a factor that shapes whether life can exist elsewhere. A planet might sit at the perfect distance from its star for liquid water, but if that star’s weather is violent enough to erode the atmosphere over geological time, habitability becomes temporary at best. Understanding our own Sun’s behavior, and what drives variations in stellar weather more broadly, feeds directly into the search for worlds that could support life.