Magnetic storm

The term “magnetic storm,” meaning a world-wide magnetic disturbance, was coined by Alexander von Humboldt (1769-1859). A naturalist who gained attention by exploring the jungles of Venezuela, Humboldt devoted much of his life to the promotion of science. He produced five volumes of “Kosmos” (starting the modern usage of that term), an encyclopaedic account covering the broad spectrum of the sciences. It was “Kosmos” which brought to the world’s attention the discovery of the sunspot cycle by Heinrich Schwabe.
After journeying through Siberia, Humboldt convinced the Czar to set up a network of magnetic observatories across the Russian lands, and additional stations were established throughout the British Empire, from Toronto to Tasmania. This network clearly showed that magnetic storms were essentially identical all over the world: a steep decrease of the field over 6-24 hours, followed by a gradual recovery which lasted 1-4 days. The change in the magnetic field was small, in modern units some 50-300 nT (nanotesla) out of a total intensity of 30-60,000 nT, but its world-wide scale suggested that something quite big was happening out in space.

The main signature of a magnetic storm is a southward magnetic field, weakening the northward field usually observed in equatorial regions. It suggests thatits origin is a “ring current” circling the Earth, and we now know that such a current does exist, carried by the outer radiation belt. In magnetic storms the outer belt becomes much more intense, reinforced by protons coming from the tail, as well as by O+ ions from the ionosphere.