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How do coronal holes create recurrent geomagnetic storms?
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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.
Coronal holes are regions on the Sun where the magnetic field is open, allowing hot material to escape and creating high-velocity streams in the solar wind.1
These holes create recurrent geomagnetic storms through the following process:
- High-Speed Streams: Coronal holes emit fast solar wind that travels significantly faster than the background solar wind.21
- Corotating Interaction Regions (CIRs): As the Sun rotates, these fast streams catch up to the slower solar wind ahead of them. This interaction creates a disturbance known as a corotating interaction region.2
- 27-Day Periodicity: Because these coronal holes can persist for several months, the resulting high-speed streams and their associated CIRs sweep past Earth repeatedly on the Sun’s 27-day rotation period.23
- Geomagnetic Impact: When these disturbances reach Earth, they interact with the magnetosphere, triggering geomagnetic storms.23
This pattern of recurrent storms is particularly prominent during the declining phase of the solar cycle and near solar minimum, when coronal holes are more prevalent than the coronal mass ejections that drive nonrecurrent storms during solar maximum.2