Britannica
Sources used in this answer
What causes a geomagnetic storm?
Created from Britannica articles
using AI.
AI can make mistakes, so verify using Britannica articles.
Space weather
Earth's full North Polar auroral oval, in an image taken in ultraviolet light by the U.S. Polar spacecraft over northern Canada, April 6, 1996. In the colour-coded image, which simultaneously shows dayside and nightside auroral activity, the most intense levels of activity are red, and the lowest levels are blue. Polar, launched in February 1996, was designed to further scientists' understanding of how plasma energy contained in the solar wind interacts with Earth's magnetosphere.
A geomagnetic storm is a major disturbance of Earth’s magnetosphere caused by variations in the solar wind and the interplanetary magnetic field (IMF). These disturbances occur when energy, mass, and momentum are transferred from the Sun to Earth’s environment, primarily through a process called magnetic reconnection.123
Key drivers of these storms include:
- Coronal Mass Ejections (CMEs): Large eruptions of magnetized plasma from the Sun’s corona. When these clouds of particles reach Earth, they can trigger intense, nonrecurrent geomagnetic storms.134
- Coronal Holes: Regions of lower gas density in the solar atmosphere that release high-speed solar wind streams. These produce recurrent storms that often follow the Sun’s 27-day rotation period.534
- Magnetic Orientation: A storm is most likely to occur when the IMF rotates to a southward orientation, becoming antiparallel to Earth’s northward-pointing magnetic field. This alignment allows for efficient energy coupling between the solar wind and the magnetosphere.534
These interactions inject plasma into the magnetosphere, creating a ring current that causes significant fluctuations in Earth's magnetic field.14