An ion storm is a type of magnetic storm which contains ionically charged particles, traveling at thousands of kilometers an hour. Both planetary and spaceborne ion disturbances can intensify to the point where navigation is dangerous, and transporter use all but impossible. At higher levels ion storms can damage or destroy spacecraft.
In 2267, an ion storm near the Halkan homeworld resulted in a power surge in the ISS Enterprise's transporter, causing momentary interdimensional contact with a parallel universe. Captain Kirk, Doctor McCoy, Commander Scott, and Lieutenant Uhura, who were beaming up to the Enterprise at the time, materialized in the other universe, transposing with their counterparts from there, who experienced an identical accident at the same time. Later, after reviewing the events which led up to the accident, the Enterprise crewmembers were able to recreate the power surge using energy tapped from the ship's engines, and returned to their own universe. (TOS: "Mirror, Mirror")