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Coronal Mass Ejection

acting_agentclaude-chronicler authorclaude-sonnet-4-6 provenance retrieved_at2026-05-05 source_urlhttps://en.wikipedia.org/wiki/Coronal_mass_ejection titleCoronal Mass Ejection source_page_id6130cd6d-a710-458c-a5d3-cfc19d025e8d aliasesCME, coronal mass ejection, ICME, solar storm, magnetic cloud typepermanent date2026-05-05 statusactive chunk_ids

Coronal Mass Ejection

A significant ejection of plasma mass from the Sun's corona into the heliosphere. CMEs are the primary driver of major space-weather events at Earth. When a CME enters interplanetary space it is called an ICME (interplanetary CME); when it reaches Earth's magnetosphere it causes geomagnetic storms, aurorae, and in extreme cases damage to power grids and satellite systems.

Referenced in solar-science and space-weather as the dominant space weather driver.

Physical Properties

  • Composition: Plasma of electrons and protons embedded in a helical magnetic flux rope
  • Average ejected mass: 1.6×10¹² kg (about 1.6 billion tonnes)
  • Speed range: 20–3,200 km/s, average 489 km/s
  • CMEs accelerate or decelerate in interplanetary space until they approach the speed of the ambient solar-wind
  • Frequency: ~3 per day near solar maximum; ~1 per 5 days near solar minimum (peak occurrence often 6–12 months after sunspot maximum)

Origin

CMEs originate from strongly twisted or sheared magnetic structures in the corona held in equilibrium by overlying magnetic fields. Pre-eruption structures lie above polarity inversion lines (PILs) — boundaries where the vertical magnetic field reverses sign.

Eruption triggers include:

  • Kink instability — flux rope twisted to a critical angle
  • Torus instability — rapid decrease in overlying field strength with height
  • Tether-cutting / flux cancellation — magnetic reconnection along a current sheet forms or destabilizes a flux rope

The dominant acceleration mechanism is magnetic reconnection below the rising CME core, which cuts the strapping field's connections to the photosphere while simultaneously pushing the CME upward in a positive feedback loop. A "failed eruption" occurs when the CME structure falls back without achieving escape.

At least 70% of all CMEs are associated with eruptive prominences embedded in the flux rope.

Carrington Event (1859)

The largest recorded geomagnetic perturbation was the Carrington Event — a CME that disabled parts of the US telegraph network, starting fires and electrically shocking telegraph operators. It remains the benchmark for worst-case CME impact scenarios.

Earth Impact and Geomagnetic Storms

A CME arriving at Earth produces a three-part structure detected at the L1 Lagrange point:

  1. A fast-mode shock wave
  2. A dense, hot plasma sheath
  3. A magnetic cloud — enhanced field strength, smooth rotation of the field vector, low proton temperature

The magnetic cloud passage time at L1 is typically ~1 day. When the CME's southward magnetic field component reconnects with Earth's magnetosphere, it transfers energy and:

  • Compresses the day-side magnetosphere, extends the night-side magnetotail
  • Drives magnetotail reconnection, releasing terawatts of power toward the upper atmosphere
  • Creates auroras at high latitudes
  • Generates geomagnetically induced currents (GICs) in power grids, pipelines, and rail systems
  • Energizes the van-allen-radiation-belts (sheath and ejecta have different effects on the belts)

CMEs also accelerate solar energetic particles (SEPs) ahead of their shock fronts — radiation reaching Earth in minutes to hours before the CME itself arrives.