Magnetic Storms

Sunspots are areas on the surface of the Sun where the solar magnetic field becomes contorted, preventing the normal flow of heat, resulting in cooler, darker areas. Related to sunspots are flares on the Sun. These are violent explosions usually lasting a few minutes. A solar flare emits vast amounts of high-energy electromagnetic (UV and X-rays) and ionized particle radiation (protons) into the solar system.

Magnetic Storm Reproduced with
permission from US National
Oceanic and Atmospheric
Administration

When a solar flare is directed towards Earth, the electromagnetic radiation, travelling at the speed of light, arrives in a little over eight minutes, synchronized with the visual observation of the event. Much of the energy of this radiation is absorbed in the ionospheric D-region (around 65km), spontaneously increasing the ionization density there, and resulting in short-wave fadeouts (SWF) and signifying the beginning of a magnetic storm. A small indicator of this type of event is a solar flare effect, immediately detectable during daylight by magnetic observatories.

The particle radiation from a solar flare, travelling at speeds of approximately 1000km per second, takes a day or two to reach Earth. Upon arrival it becomes compressed and generates a shockwave in Earth's magnetic field which is recorded by magnetic observatories around the globe. A sudden step in the magnetic field is observed, followed by large excursions in the field's intensity and orientation. Such magnetic storms can last from a few hours to several days.

During magnetic storms huge electric currents flow in Earth's ionosphere. They may cause inaccuracies in compass readings, radio broadcasts to be received in areas far from where they were intended and auroras to be seen at latitudes much nearer the equator than usual. People may report lost homing pigeons or experience GPS problems and currents may be induced in long conductors such as pipelines and powerlines.

Topic contact: geomag@ga.gov.au Last updated: May 8, 2013