A major (sometimes global) disturbance of the Earth’s magnetosphere caused by high-speed streams of solar wind such as from coronal mass ejections and coronal holes. Rapid fluctuations in the magnetic field strength and direction follow the onset of the storm, with a gradual return to normal over perhaps 2–3 days. Geomagnetic storms are often accompanied by active displays of aurora, extending to lower latitudes than normal. At such times the Kp index rises to 5 or more. Electrical currents in the ground induced during geomagnetic storms can damage power grid systems. The associated auroral effects can wreak havoc with short-wave radio communication, while currents flowing in the ionosphere can damage artificial satellites.