How do coronal mass ejections cause geomagnetic storms and voltage surges?

Coronal mass ejections (CMEs) are large eruptions of magnetized plasma from the Sun’s corona that propagate into interplanetary space. They cause geomagnetic storms primarily through the process of magnetic reconnection.1

How Geomagnetic Storms Occur

When a CME reaches Earth, its magnetic field—particularly if it contains a strong southward-pointing component—couples with Earth’s northward-pointing geomagnetic field. This interaction allows energy, mass, and momentum from the solar wind to be transferred into Earth’s magnetosphere. This process energizes charged particles, which form a ring current around the magnetosphere, leading to sharp fluctuations in Earth’s magnetic field known as geomagnetic storms.123

Voltage Surges

The energy transferred during these storms generates electric currents that flow through the ionosphere. These ionospheric currents can induce additional voltages and currents in long-distance conductors on the ground, such as power distribution systems and pipelines. These enhanced currents can damage electrical transformers, potentially causing widespread power grid failures.4523