Coronal Mass Ejection
A large-scale expulsion of plasma and magnetic field from the Sun's corona that travels through interplanetary space and can interact with Earth's magnetosphere.
Explanation
CMEs are among the most powerful space weather events. Unlike flares, which produce radiation that arrives in minutes, CMEs are clouds of magnetized plasma that take 1-4 days to reach Earth. When a CME arrives, it compresses Earth's magnetosphere and can trigger geomagnetic storms. The severity depends on the CME's speed, magnetic field orientation, and density. Fast CMEs (over 1,000 km/s) produce the strongest storms. Key effects include intensified aurora, geomagnetically induced currents in power lines, satellite drag augmentation, and radiation belt enhancement. The Carrington Event of 1859 — the most extreme recorded geomagnetic storm — was caused by a CME that set telegraph wires on fire. Modern society's reliance on electronics and power grids makes CME impacts far more consequential. Space weather forecasters use coronagraph imagery from SOHO and the GOES-R series to detect CMEs and predict their arrival.
Why It Matters
CMEs are the primary driver of severe geomagnetic storms. A Carrington-class CME hitting modern infrastructure could cause trillions of dollars in damage to power grids, satellites, and communications networks.
Concept Map
How Coronal Mass Ejection connects to other glossary terms:
Frequently Asked Questions
What is the difference between a CME and a solar flare?
A flare is a flash of electromagnetic radiation; a CME is a physical ejection of plasma. Flares reach Earth in minutes; CMEs take days. They often occur together but can happen independently.
How is a CME detected?
Coronagraphs on spacecraft like SOHO and GOES block out the Sun's bright disk to image the faint corona. CMEs appear as expanding clouds of plasma moving outward.
Sources
Last updated: July 1, 2026