Magnetic Storms

The magnetic storm is about the first of several aspects of the earth's environment to be recognized as caused by variations on the sun. During the last century, people noticed that there were occasional periods of a day or longer when the magnetic field of the earth changed in strength and direction. They called these periods magnetic storms.

Later, scientists realized that the times of magnetic storm were the times of most extensive auroral displays, and they realized that magnetic storms typically followed, by a day or two, large flares on the sun. When radio came into use about 60 years ago, people soon found that long-distance radio propagation was erratic or impossible during magnetic storms.

Erupting solar flares, typically associated with major sunspots, spew out large numbers of charged particles, mostly electrons and protons which stream outward to the earth to create the magnetic storms and related phenomena.

During storms, intense electrical currents flow in the earth's ionosphere, especially in the auroral zones. These currents--as do all currents--generate magnetic fields. Just as the aurora is quite variable, the auroral zone ionospheric currents are variable and it is their created magnetic fields that are most responsible for the jumpiness of a compass needle placed at high latitude. Variations of a large fraction of a degree commonly occur, and variations by several degrees in a few minutes time have been observed.

Magnetic storms often last for several days, but the first day usually is the most severe. The bright, extensive auroras often seen near the onset of the storm typically will be followed the next night by a somewhat lesser display, and the night after that usually will have fewer still. It is hard to predict major auroral displays, but the knowledge that they are related to magnetic storms helps.