Space Weather at a Glance
Space weather refers to the variable conditions in the space environment between the Sun and Earth — driven primarily by activity on the Sun's surface. Just as terrestrial weather describes rain, wind and temperature on the ground, space weather describes the flow of energetic particles, electromagnetic radiation and magnetised plasma through interplanetary space and into Earth's magnetosphere.
For most of human history, space weather was invisible and irrelevant. Today, with over 14,000 active satellites in orbit, billions of people relying on GPS, and power grids spanning entire continents, space weather is an operational concern that affects technology, infrastructure and even astronaut safety on a daily basis.
The Sun: The Engine of Space Weather
All space weather originates at the Sun. Our star continuously emits a stream of charged particles — mostly protons and electrons — known as the solar wind. This wind flows outward at roughly 400 km/s on average, though high-speed streams from coronal holes can exceed 800 km/s. The solar wind shapes the heliosphere — the vast bubble of space under the Sun's influence — and constantly interacts with Earth's magnetosphere.
Superimposed on this steady background are episodic, often violent, events:
Solar Flares
A solar flare is a sudden, intense burst of electromagnetic radiation from the Sun's surface, typically associated with active regions (sunspots). Flares are classified by peak X-ray flux: B, C, M and X class, with X-class flares being the most powerful. The radiation from a flare reaches Earth at the speed of light — about 8 minutes — making it impossible to provide advance warning. Strong flares cause immediate radio blackouts on Earth's sunlit side, disrupting high-frequency (HF) aviation and marine communications.
Coronal Mass Ejections (CMEs)
A coronal mass ejection is a massive cloud of magnetised plasma ejected from the Sun's corona, often associated with flares but sometimes occurring independently. CMEs can carry billions of tonnes of solar material and travel at speeds from 250 km/s to over 3,000 km/s. A fast, Earth-directed CME typically takes 1–3 days to reach our planet. When a CME's magnetic field connects with Earth's magnetosphere, it can trigger a geomagnetic storm — the most impactful type of space weather event for satellites and ground infrastructure.
Solar Energetic Particles (SEPs)
SEPs are high-energy protons and ions accelerated by solar flares or CME-driven shock waves. They arrive at Earth within minutes to hours of the parent event and can penetrate spacecraft shielding, causing single-event upsets (bit flips) in satellite electronics, degrading solar panels, and posing a radiation hazard to astronauts and aircrew on high-latitude polar routes.
Co-Rotating Interaction Regions (CIRs)
When a high-speed solar wind stream overtakes slower wind ahead of it, the boundary between them compresses into a CIR. These structures rotate with the Sun and can produce recurrent mild to moderate geomagnetic disturbances, typically every 27 days (one solar rotation).
Geomagnetic Storms
When a CME or high-speed solar wind stream disturbs Earth's magnetosphere, the result is a geomagnetic storm. Storms are measured on the Kp index (0–9) and NOAA's G-scale (G1 minor to G5 extreme). During a storm, the magnetosphere compresses on the dayside and stretches on the nightside, driving electric currents in the ionosphere and magnetosphere that produce a cascade of effects:
- Atmospheric expansion — heating of the thermosphere increases neutral density at satellite altitudes, dramatically raising drag on LEO satellites. This is the mechanism that destroyed 40 Starlink satellites in February 2022.
- Satellite charging — energetic particles accumulate on spacecraft surfaces, creating voltage differentials that can arc and damage electronics.
- GPS degradation — ionospheric disturbances refract and delay GNSS signals, reducing positioning accuracy. See our Space Weather & GPS guide.
- Geomagnetically induced currents (GICs) — ground-level currents can flow through power lines, pipelines and railway tracks, potentially damaging transformers. The 1989 Hydro-Québec blackout left 6 million people without power for 9 hours due to a geomagnetic storm.
- Auroras — the visible result of energetic particles exciting atmospheric gases, producing green, red and purple displays at high latitudes (and at lower latitudes during major storms).
The Solar Cycle
Solar activity rises and falls on an approximately 11-year cycle. The number of sunspots — dark, magnetically active regions on the Sun's surface — increases from solar minimum to solar maximum, and the frequency and intensity of flares, CMEs and SEP events rises correspondingly.
We are currently in Solar Cycle 25, which began in December 2019. Cycle 25 has significantly exceeded initial predictions: NOAA's Solar Cycle Prediction Panel originally forecast a relatively weak cycle with a peak sunspot number of around 115, but observed activity surged well past that, with monthly sunspot numbers exceeding 200 in mid-to-late 2024. The cycle appears to have reached or neared its maximum during late 2024 to early 2025, producing some of the most intense space weather events since the Halloween Storms of 2003 — including the G5-class geomagnetic storm of May 2024, the strongest in over two decades.
Notable Space Weather Events in History
| Event | Date | Severity | Impact |
|---|---|---|---|
| Carrington Event | Sep 1859 | Estimated Dst –1,760 nT | Largest recorded geomagnetic storm. Telegraph systems shocked operators and operated without power. Auroras seen at the equator. |
| May 1921 Storm | May 1921 | Estimated Dst –907 nT | Telegraph infrastructure damaged worldwide; fires reported at telegraph stations in Sweden. |
| Quebec Blackout | Mar 1989 | Kp 9, G5 | GICs collapsed Hydro-Québec grid in 92 seconds, blacking out 6 million people for 9 hours. |
| Bastille Day Event | Jul 2000 | X5.7 flare | Damaged ASCA X-ray satellite (later deorbited). Widespread HF radio blackouts. |
| Halloween Storms | Oct–Nov 2003 | X17+ flares, G5 | Satellite anomalies across dozens of spacecraft. GOES-13 imager damaged. Swedish power grid tripped. Astronauts on ISS sheltered. |
| May 2024 Superstorm | May 2024 | G5, Kp 9 | Strongest geomagnetic storm since 2003. Auroras visible across southern Europe and the US southern states. Multiple GNSS disruptions reported. |
Who Monitors Space Weather?
Several agencies worldwide provide operational space weather forecasting and alerts:
- NOAA Space Weather Prediction Center (SWPC) — the primary US civilian forecast office, issuing watches, warnings and alerts for geomagnetic storms, solar radiation storms and radio blackouts.
- ESA Space Weather Service Network — provides space weather services to European stakeholders, including spacecraft operators and aviation.
- UK Met Office Space Weather Operations Centre (MOSWOC) — one of three ICAO-designated global space weather advisory centres for aviation.
- ISES (International Space Environment Service) — coordinates international space weather monitoring through regional warning centres in over a dozen countries.
Key observing assets include the DSCOVR and ACE spacecraft stationed at the Sun-Earth L1 Lagrange point (about 1.5 million km sunward of Earth), which provide 15–60 minutes of advance warning before a CME or solar wind disturbance arrives at Earth.
Why Space Weather Matters for Orbital Radar Users
If you're tracking satellites, space weather is not abstract — it directly affects what you see on the globe. During a geomagnetic storm, the increased atmospheric drag can cause LEO satellites to drop altitude faster than their TLE propagation models predict, meaning orbital positions can drift from their calculated tracks. Major storms can also cause temporary tracking gaps as radar and optical systems are affected. Understanding the space weather context behind what you're watching makes you a better-informed observer of the orbital environment.