Parameter Tree:
EARTH SCIENCE > SUN-EARTH INTERACTIONS > IONOSPHERE/MAGNETOSPHERE DYNAMICS > MAGNETIC STORMS

Definition:
A magnetic storm is a large-scale disturbance of the magnetosphere, often
initiated by the arrival of an interplanetary shock originating at the Sun. A
magnetic storm is marked by the injection of an appreciable number of ions from
the magnetotail into the ring current, a process accompanied by increased
auroral displays. The strengthened ring current causes a world-wide drop in the
equatorial magnetic field, taking perhaps 12 hours to reach its greatest
intensity, followed by a more gradual recovery.


Reference:
http://www-istp.gsfc.nasa.gov/Education/gloss.html