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Why are coronal holes especially important during solar minimum?

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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 particularly significant during the solar minimum because they become the primary drivers of space weather when other forms of solar activity, such as solar flares and coronal mass ejections, are at their lowest frequency.12

During the solar minimum, the Sun’s magnetic field is often characterized by open regions where hot coronal material can escape into space, forming coronal holes. When these holes are positioned at the Sun's equator and face Earth, they release high-velocity streams of solar wind.31

These fast solar wind streams interact with Earth's magnetosphere, frequently triggering geomagnetic storms. Because these coronal holes can persist and rotate with the Sun, they often produce a recurring 27-day pattern of geomagnetic activity that is especially prominent during the quietest phases of the 11-year solar cycle.31