---
source: https://iinventedlight.com/library/notes/coronal-mass-ejections.md
title: "Coronal mass ejections and geomagnetic storms"
license: CC-BY-4.0
license_url: https://creativecommons.org/licenses/by/4.0/
source_license: "US government work, public domain; restated in our own words"
attribution: "Summary by iinventedlight (AI-assisted). Sources: NOAA, Coronal Mass Ejections, US government work, public domain; NOAA, Geomagnetic Storms, US government work, public domain."
author: "iinventedlight (synthesis of cited sources); text drafted with AI assistance"
date: 2026-11-04
status: published
checked_on: 2026-11-04
as_of: 2026-11-04
confidence: medium
untested: "No observation or experiment was done; only the fetched government pages were read."
category: coverage-gaps
topic_area: "space: space weather"
tags: ['space-weather', 'sun', 'cme', 'aurora']
sources:
  - id: S1
    title: "Coronal Mass Ejections"
    publisher: NOAA
    url: https://www.swpc.noaa.gov/phenomena/coronal-mass-ejections
    accessed: 2026-11-04
    license: "US government work, public domain"
  - id: S2
    title: "Geomagnetic Storms"
    publisher: NOAA
    url: https://www.swpc.noaa.gov/phenomena/geomagnetic-storms
    accessed: 2026-11-04
    license: "US government work, public domain"
---
# Coronal mass ejections and geomagnetic storms

**Answer:** A coronal mass ejection (CME) is a huge cloud of plasma and magnetic field thrown off the Sun's corona. Fast Earth-directed CMEs can arrive in 15 to 18 hours (most take days) and cause the largest geomagnetic storms, which bring aurora but can disrupt GPS, satellites and power grids.

## What a CME is

CMEs can carry billions of tons of material at speeds from under 250 km/s to nearly 3000 km/s. Explosive ones begin when twisted magnetic structures in the lower corona snap into a calmer shape (magnetic reconnection), often with a flare.

## Watching them

Forecasters estimate size, speed and direction from coronagraph images, mainly SOHO's LASCO. The DSCOVR satellite at L1 then gives 15 to 60 minutes' warning of arrival.

## Geomagnetic storms

A storm occurs when energy transfers efficiently from the solar wind into Earth's magnetosphere, especially when the CME's magnetic field points south. Effects include:

- extra drag on low-orbit satellites,
- GPS and navigation errors,
- induced currents in power grids and pipelines,
- auroras.

## Claims
- id: C1
  claim: CMEs are large expulsions of plasma and magnetic field from the corona.
  source: S1
  evidence: "Coronal Mass Ejections (CMEs) are large expulsions of plasma and magnetic field from the Sun’s"
- id: C2
  claim: The fastest Earth-directed CMEs can arrive in 15-18 hours.
  source: S1
  evidence: "The fastest Earth-directed CMEs can reach our planet in as little as 15-18 hours."
- id: C3
  claim: DSCOVR can give 15 to 60 minutes advance warning.
  source: S1
  evidence: "This can often provide 15 to 60 minutes advanced warning of shock arrival at Earth"
- id: C4
  claim: The largest geomagnetic storms are associated with CMEs.
  source: S2
  evidence: "The largest storms that result from these conditions are associated with solar coronal mass ejections"
- id: C5
  claim: Storms can disrupt navigation systems such as GNSS.
  source: S2
  evidence: "they also can disrupt navigation systems such as the Global Navigation Satellite System (GNSS)"

## Sources
- [S1] Coronal Mass Ejections. NOAA. https://www.swpc.noaa.gov/phenomena/coronal-mass-ejections . License: US government work, public domain. Accessed 2026-11-04.
- [S2] Geomagnetic Storms. NOAA. https://www.swpc.noaa.gov/phenomena/geomagnetic-storms . License: US government work, public domain. Accessed 2026-11-04.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted).