Coronal mass ejections: The link between solar and geomagnetic activity*

Coronal mass ejections are spectacular manifestations of solar activity in which 10+15–10+16 g of solar material are propelled outward into interplanetary space. Recent work has demonstrated that these events are the prime link between solar activity and large, nonrecurrent geomagnetic storms, closing a loop in a body of research extending back more than 130 years.