geomagnetic storms

Also found in: Dictionary.

geomagnetic storms

(jee-oh-mag-net -ik) Sudden alterations in and subsequent recovery of the Earth's magnetic field due to the effects of solar flares. The variations are complex in the auroral zone and polar regions but at middle latitudes the horizontal component of the field shows four distinct phases.

The first is storm sudden commencement (SSC), when a sharp rise in field strength (over 2.5 to 5 minutes) is caused by compression of the magnetosphere by a flare-generated shock wave. The second is the initial phase (IP), when the Earth is surrounded by the high-speed post-shock plasma and field, and is effectively isolated (for between about 30 minutes and several hours) from the interplanetary magnetic field. The surface field strength is higher than the pre-SSC value. In the main phase (MP) an increase in particle population, or in particle acceleration by reconnection of the geomagnetic and interplanetary fields, or in magnetospheric fluctuations produces a ring current at three to five Earth radii. This generates a magnetic field opposed to the Earth's and causes a decrease in the surface field strength of 50–400 nanoteslas, which lasts from a few hours to more than a day. During the fourth phase, recovery phase (RP), which is typically longer than the MP, the ring current decays by diffusion of the trapped particles and plasma instabilities. The surface field strength may return to, or just below, the pre-SSC value.

Geomagnetic storms are usually accompanied by ionospheric and auroral activity, and some may recur after 27 days owing to the persistence of a particular solar active region or coronal hole.

References in periodicals archive ?
Geomagnetic storms tend to be most prevalent in regions where Earth's magnetic field is unusually weak.
The present study was based upon the observation that geomagnetic storm conditions influenced microvolt fluctuations within coronal sections of fixed human brain tissue.
Forecasts predicted a geomagnetic storm would hit Earth that night and potentially create beautiful aurora.
Therefore, protection against the next large geomagnetic storm is the topic being addressed by a number of respected scientists.
Scientists later determined that a solar coronal mass ejection had hit Earth's magnetosphere and induced one of the largest geomagnetic storms on record.
Geomagnetic storms increase the earth's magnetic field and are most familiar to us in the context of aurora in high-latitude regions of earth and for disrupting satellite communication.
The destructive phenomenon of High-altitude ElectroMagnetic Pulse or Hemp can be caused either by the detonation of a nuclear missile high in the atmosphere or by space weather such as solar flares and geomagnetic storms.
When such geomagnetic storms happen, their beauty can be as immense as their potential for danger.
Factors like a city's geomagnetic latitude, ground conductivity and distance from the coast's highly conducive seawater can make certain regions more susceptible to geomagnetic storms than other.
Since Mars lacks a planet-wide magnetic field, it does not experience geomagnetic storms.
And according to a report by Aon Benfield, these geomagnetic storms are of particular concern today since solar activity typically follows an 11-year cycle and its next peak may be occurring right now.
During geomagnetic storms that produce extremely bright auroras shimmering all across the sky, only circular fisheye lenses, such as an 8-mm fisheye, can record the entire sky in a single frame.