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How do solar flares and coronal holes cause geomagnetic storms?

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geomagnetic field The magnetic field of a bar magnet has a simple configuration known as a dipole field. Close to Earth's surface this field is a reasonable approximation of the actual field.

Geomagnetic storms are disturbances in Earth’s magnetosphere caused by changes in the solar wind and the interplanetary magnetic field (IMF).12

Coronal Holes and Recurrent Storms

Coronal holes are regions in the Sun’s atmosphere where gas density is low, allowing charged particles to escape easily and form high-speed solar wind streams. When these streams interact with slower-moving solar wind, they create corotating interaction regions that tilt the IMF. If this tilted field becomes antiparallel to Earth’s geomagnetic field, it triggers a geomagnetic storm. Because coronal holes can persist for months, they often produce recurrent storms that repeat on a 27-day solar rotation cycle.3415

Solar Flares and Nonrecurrent Storms

Solar flares are explosive releases of energy in the solar corona. While flares and coronal mass ejections (CMEs) can occur independently, they are both manifestations of magnetic reconnection. Fast CMEs, often associated with flares, drive interplanetary shocks that cause the most intense, nonrecurrent geomagnetic storms. These storms occur when the CME’s magnetic field couples with Earth’s magnetosphere, transferring mass and momentum.316