A geomagnetic storm, or solar storm, is a temporary disturbance of the Earth's magnetosphere caused by a disturbance in space weather. Associated with solar coronal mass ejections (CME), coronal holes, or solar flares, a geomagnetic storm is caused by a solar wind shock wave which typically strikes the Earth's magnetic field 24 to 36 hours after the event. This only happens if the shock wave travels in a direction toward Earth. The solar wind pressure on the magnetosphere will increase or decrease depending on the Sun's activity. These solar wind pressure changes modify the electric currents in the ionosphere. Magnetic storms usually last 24 to 48 hours, but some may last for many days. In 1989, an electromagnetic storm disrupted power throughout most of Quebec — it caused auroras as far south as Texas .
On 13 March, 1989 a severe geomagnetic storm caused the collapse of the Hydro-Québec power grid in a matter of seconds as equipment protection relays tripped in a cascading sequence of events . Six million people were left without power for nine hours, with significant economic loss. The storm even caused auroras as far south as Texas . The geomagnetic storm causing this event was itself the result of a Coronal Mass Ejection, ejected from the Sun on March 9, 1989.
In August 1989, another storm affected micro chips, leading to a halt of all trading on Toronto's stock market .
Since 1989 power companies in North America, the UK, Northern Europe and elsewhere have invested time and effort in evaluating the geomagnetically induced current (GIC) risk and in developing mitigation strategies.
Since 1995, geomagnetic storms and solar flares are observed from the Solar and Heliospheric Observatory (SOHO) joint-NASA-European Space Agency satellite.
Interactions with planetary processes
The solar wind also carries with it the magnetic field of the Sun. This field will have either a North or South orientation. If the solar wind has energetic bursts, contracting and expanding the magnetosphere, or if the solar wind takes a southward polarization, geomagnetic storms can be expected. The southward field causes magnetic reconnection of the dayside magnetopause, rapidly injecting magnetic and particle energy into the Earth's magnetosphere.
During a geomagnetic storm, the ionosphere's F2 layer will become unstable, fragment, and may even disappear. In the Northern and Southern pole regions of the Earth, auroras (aka Northern lights) will be observable in the sky.
Geomagnetic storm effects
Radiation hazards to humans
Intense solar flares
release very-high-energy particles that can be as injurious to humans as the low-energy radiation from nuclear blasts
. Earth's atmosphere
allow adequate protection at ground level, but astronauts
in space are subject to potentially lethal doses of radiation
. The penetration of high-energy particles into living cells can cause chromosome
, and a host of other health problems. Large doses can be fatal immediately. Solar protons
with energies greater than 30 Megaelectronvolts(MeV) are particularly hazardous. In October 1989
, the Sun produced enough energetic particles that an astronaut on the Moon
, wearing only a space suit
and caught out in the brunt of the storm, would probably have died; the expected dose would be about 7000 rem
. (Astronauts who had time to gain safety in a shelter beneath moon soil would have absorbed only slight amounts of radiation.) The astronauts on the Mir
station were subjected to daily doses of about twice the yearly dose on the ground, and during the solar storm at the end of 1989 they absorbed their full-year radiation dose limit in just a few hours.
Solar proton events can also produce elevated radiation aboard aircraft flying at high altitudes. Although these risks are small, monitoring of solar proton events by satellite instrumentation allows the occasional exposure to be monitored and evaluated, and eventually the flight paths and altitudes adjusted in order to lower the absorbed dose of the flight crews.
There is a growing body of evidence that changes in the geomagnetic field affect biological systems. Studies indicate that physically stressed human biological systems may respond to fluctuations in the geomagnetic field. Interest and concern in this subject have led the International Union of Radio Science
to create a new commission entitled Commission K - Electromagnetics in Biology and Medicine
Current chair Dr. Frank Prato
Possibly the most closely studied of the variable Sun's biological effects has been the degradation of homing pigeons' navigational abilities during geomagnetic storms. Pigeons and other migratory animals, such as dolphins and whales, have internal biological compasses composed of the mineral magnetite wrapped in bundles of nerve cells. While this probably is not their primary method of navigation, there have been many pigeon race smashes, a term used when only a small percentage of birds return home from a release site. Because these losses have occurred during geomagnetic storms, pigeon handlers have learned to ask for geomagnetic alerts and warnings as an aid to scheduling races.
Many communication systems use the ionosphere to reflect radio signals over long distances. Ionospheric storms can affect radio communication at all latitudes. Some radio frequencies are absorbed and others are reflected, leading to rapidly fluctuating signals and unexpected propagation
paths. TV and commercial radio stations are little affected by solar activity, but ground-to-air, ship-to-shore, shortwave broadcast
, and amateur radio
(mostly the bands below 30 MHz) are frequently disrupted. Radio operators using HF bands rely upon solar and geomagnetic alerts to keep their communication circuits up and running.
Some military detection or early warning systems are also affected by solar activity. The over-the-horizon radar bounces signals off the ionosphere in order to monitor the launch of aircraft and missiles from long distances. During geomagnetic storms, this system can be severely hampered by radio clutter. Some submarine detection systems use the magnetic signatures of submarines as one input to their locating schemes. Geomagnetic storms can mask and distort these signals.
The Federal Aviation Administration routinely receives alerts of solar radio bursts so that they can recognize communication problems and forego unnecessary maintenance. When an aircraft and a ground station are aligned with the Sun, jamming of air-control radio frequencies can occur. This can also happen when an Earth station, a satellite, and the Sun are in alignment.
The telegraph lines in the past were affected by geomagnetic storms as well. The telegraphs used a long wire for the data line, stretching for many miles, using ground as the return wire and being fed with DC power from a battery; this made them (together with the power lines mentioned below) susceptible to being influenced by the fluctuations caused by the ring current. The voltage/current induced by the geomagnetic storm could have led to diminishing of the signal, when subtracted from the battery polarity, or to overly strong and spurious signals when added to it; some operators in such cases even learned to disconnect the battery and rely on the induced current as their power source. In extreme cases the induced current was so high the coils at the receiving side burst in flames, or the operators received electric shocks. Geomagnetic storms affect also long-haul telephone lines, including undersea cables if they aren't fiber optic based.
Systems such as GPS
, and the now-defunct OMEGA
are adversely affected when solar activity disrupts their signal propagation. The OMEGA system consisted of eight transmitters located throughout the world. Airplanes and ships used the very low frequency signals from these transmitters to determine their positions. During solar events and geomagnetic storms, the system gave navigators information that is inaccurate by as much as several miles. If navigators had been alerted that a proton event or geomagnetic storm is in progress, they could have switched to a backup system.
GPS signals are affected when solar activity causes sudden variations in the density of the ionosphere, causing the GPS signals to scintillate. The scintillation of satellite signals during ionospheric disturbances is studied at HAARP during ionospheric modification experiments. It has also been studied at the Jicamarca Radio Observatory.
Geomagnetic storms and increased solar ultraviolet
emission heat Earth's upper atmosphere, causing it to expand. The heated air rises, and the density at the orbit of satellites
up to about 1000 km increases significantly. This results in increased drag
on satellites in space, causing them to slow and change orbit
slightly. Unless Low Earth Orbit
satellites are routinely boosted to higher orbits, they slowly fall, and eventually burn up in Earth's atmosphere.
Skylab is an example of a spacecraft reentering Earth's atmosphere prematurely in 1979 as a result of higher-than-expected solar activity. During the great geomagnetic storm of March 1989, four of the Navy's navigational satellites had to be taken out of service for up to a week, the U.S. Space Command had to post new orbital elements for over 1000 objects affected, and the Solar Maximum Mission satellite was sent towards meeting the Skylab fate in December the same year.
The vulnerability of the satellites depends on their position as well. The South Atlantic Anomaly is a perilous place for a satellite to pass through.
As technology has allowed spacecraft components to become smaller, their miniaturized systems have become increasingly vulnerable to the more energetic solar particles. These particles can cause physical damage to microchips and can change software commands in satellite-borne computers.
Another problem for satellite operators is differential charging
. During geomagnetic storms, the number and energy of electrons
increase. When a satellite travels through this energized environment, the charged particles
striking the spacecraft cause different portions of the spacecraft to be differentially charged
. Eventually, electrical discharges can arc
across spacecraft components, harming and possibly disabling them.
(also called deep charging
) occurs when energetic particles, primarily electrons, penetrate the outer covering of a satellite and deposit their charge in its internal parts. If sufficient charge accumulates in any one component, it may attempt to neutralize by discharging to other components. This discharge is potentially hazardous to the satellite's electronic systems.
Earth's magnetic field is used by geologists to determine subterranean rock structures. For the most part, these geodetic surveyors are searching for oil, gas, or mineral deposits. They can accomplish this only when Earth's field is quiet, so that true magnetic signatures can be detected. Other surveyors prefer to work during geomagnetic storms, when the variations to Earth's normal subsurface electric currents help them to see subsurface oil or mineral structures. For these reasons, many surveyors use geomagnetic alerts and predictions to schedule their mapping activities.
When magnetic fields
move about in the vicinity of a conductor such as a wire, a geomagnetically induced current
is produced into the conductor. This happens on a grand scale during geomagnetic storms (the same mechanism also influences telephone and telegraph lines, see above). Power companies transmit alternating current to their customers via long transmission lines. The nearly direct currents induced in these lines from geomagnetic storms are harmful to electrical transmission equipment, especially to the transformers
—it overheats their coils and causes saturation
of their cores, constraining their performance; it also tends to trip various protective devices. Potentially the heat generated in the iron cores of the generators can destroy them and chain reaction could blow transformers throughout a system. On March 13
, in Québec
, 6 million people were without commercial electric power for 9 hours as a result of a huge geomagnetic storm. Some areas in the northeastern U.S. and in Sweden also lost power. By receiving geomagnetic storm alerts and warnings, power companies can minimize damage and power outages.
Worst case scenarios include Geomagnetic storm with the potential to damage power supply equipment world wide that would lead power blackouts of years while equipment was being replaced. While this damage could be avoided this would require decision makers being willing to shut down the power system in advance.
Rapidly fluctuating geomagnetic fields can produce geomagnetically induced currents
also into pipelines
. During these times, several problems can arise for pipeline engineers. Flow meters in the pipeline can transmit erroneous flow information, and the corrosion
rate of the pipeline is dramatically increased. If engineers unwittingly attempt to balance the current during a geomagnetic storm, corrosion rates may increase even more. Pipeline managers routinely receive alerts and warnings to help them provide an efficient and long-lived system.
A wide range of ground based magneto spheric observations exist. Magnetometers
monitor the auroral zone as well as the equatorial region. Two types of radar
- coherent scatter and incoherent scatter - are used to probe the auroral ionosphere. By bouncing signals off ionospheric irregularities (which convect with their field lines) one can trace their motion and infer magnetospheric convection.
Spacecraft instruments include:
- Magnetometers, usually of the flux gate type. Usually these are at the end of booms, to keep them away from magnetic interference by the spacecraft and its electric circuits.
- Electric sensors at the ends of opposing booms are used to measure potential differences between separated points, to derive electric field associated with convection. The method works best at high plasma densities in low Earth orbit; far from Earth long booms are needed, to avoid shielding-out of electric forces.
- Radio sounders from the ground can bounce radio waves of varying frequency off the ionosphere, and by timing their return get the profile of electron density in the ionosphere - up to its peak, past which radio waves no longer return. Radio sounders in low Earth orbit aboard the Canadian Alouette (1962) and Alouette 2 (1965), beamed radio waves earthward and observed the electron density profile of the "topside ionosphere." Other radio sounding methods were also tried in the ionosphere (e.g. on IMAGE).
- A great variety of "particle detectors" has operated in orbit. The original observations of the Van Allen radiation belt used a Geiger counter, a crude detector unable to tell particle charge or energy. Later scintillator detectors were used, and still later "channeltron" electron multipliers have found particularly wide use. To derive charge and mass composition, as well as energies, a variety of mass spectrograph designs were used. For energies up to about 50 keV (which constitute most of the magnetospheric plasma) time-of-flight spectrometers (e.g. "top-hat" design) are widely used.
- Computers are not usually viewed as scientific instruments, but they have been indispensable in magnetospheric research, and not just by pre-processing complex satellite data for more economical transmission of data to the ground. Computers have also made it possible to bring together decades of isolated magnetic observations and extract average patterns of electrical currents and average responses to interplanetary variations.
A different application are simulations of the global magnetosphere and its responses, by solving the equations of magnetohydrodynamics (MHD) on a numerical grid. Appropriate extensions must be added to cover the inner magnetosphere, where magnetic drifts and ionospheric conduction also need to be taken into account. So far the results are interesting, but their interpretation is not easy, and certain assumptions are still needed to cover small-scale phenomena.
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Aurora Watch, at the University of Lancashire, gives email warnings of coronal mass ejections and geomagnetic storms for aurora watching enthusiasts: