Geomagnetic storm
A geomagnetic storm, also known as a magnetic storm, is a temporary disturbance of the Earth's magnetosphere caused by a solar wind shock wave.
This article is about disturbances within Earth's magnetosphere. For other uses of "magnetic storm", see Magnetic storm (disambiguation).
The disturbance that drives the magnetic storm may be a solar coronal mass ejection (CME) or (much less severely) a co-rotating interaction region (CIR), a high-speed stream of solar wind originating from a coronal hole.[1] The frequency of geomagnetic storms increases and decreases with the sunspot cycle. During solar maximum, geomagnetic storms occur more often, with the majority driven by CMEs.
The increase in the solar wind pressure initially compresses the magnetosphere. The solar wind's magnetic field interacts with the Earth's magnetic field and transfers an increased energy into the magnetosphere. Both interactions cause an increase in plasma movement through the magnetosphere (driven by increased electric fields inside the magnetosphere) and an increase in electric current in the magnetosphere and ionosphere. During the main phase of a geomagnetic storm, electric current in the magnetosphere creates a magnetic force that pushes out the boundary between the magnetosphere and the solar wind.
Several space weather phenomena tend to be associated with or are caused by a geomagnetic storm. These include solar energetic particle (SEP) events, geomagnetically induced currents (GIC), ionospheric storms and its disturbances that cause radio and radar scintillation, disruption of navigation by magnetic compass and auroral displays at much lower latitudes than normal.
The largest recorded geomagnetic storm, the Carrington Event in September 1859, took down parts of the recently created US telegraph network, starting fires and electrically shocking telegraph operators.[2] In 1989, a geomagnetic storm energized ground induced currents that disrupted electric power distribution throughout most of Quebec[3] and caused aurorae as far south as Texas.[4] The Carrington Event was mild compared with very rare extreme geomagnetic storms called Miyake events, which cause spikes in radioactive carbon-14 in tree rings.
Geomagnetic storm intensity is reported in several different ways, including:
History of the theory[edit]
In 1930, Sydney Chapman and Vincenzo C. A. Ferraro wrote an article, A New Theory of Magnetic Storms, that sought to explain the phenomenon.[10] They argued that whenever the Sun emits a solar flare it also emits a plasma cloud, now known as a coronal mass ejection. They postulated that this plasma travels at a velocity such that it reaches Earth within 113 days, though we now know this journey takes 1 to 5 days. They wrote that the cloud then compresses the Earth's magnetic field and thus increases this field at the Earth's surface.[11] Chapman and Ferraro's work drew on that of, among others, Kristian Birkeland, who had used recently-discovered cathode ray tubes to show that the rays were deflected towards the poles of a magnetic sphere. He theorised that a similar phenomenon was responsible for auroras, explaining why they are more frequent in polar regions.
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 move with the field lines, one can trace their motion and infer magnetospheric convection.
Spacecraft instruments include:
Computers have made it possible to bring together decades of isolated magnetic observations and extract average patterns of electrical currents and average responses to interplanetary variations. They also run 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 need to be taken into account. At polar regions, directly linked to the solar wind, large-scale ionospheric anomalies can be successfully modeled, even during geomagnetic super-storms. [26] At smaller scales (comparable to a degree of latitude/longitude) the results are difficult to interpret, and certain assumptions about the high-latitude forcing uncertainty are needed. [27]
Geomagnetic storm effects[edit]
Disruption of electrical systems[edit]
It has been suggested that a geomagnetic storm on the scale of the solar storm of 1859 today would cause billions or even trillions of dollars of damage to satellites, power grids and radio communications, and could cause electrical blackouts on a massive scale that might not be repaired for weeks, months, or even years.[23] Such sudden electrical blackouts may threaten food production.[28]
Main electrical grid[edit]
When magnetic fields move about in the vicinity of a conductor such as a wire, a geomagnetically induced current is produced in the conductor. This happens on a grand scale during geomagnetic storms (the same mechanism also influenced telephone and telegraph lines before fiber optics, see above) on all long transmission lines. Long transmission lines (many kilometers in length) are thus subject to damage by this effect. Notably, this chiefly includes operators in China, North America, and Australia, especially in modern high-voltage, low-resistance lines. The European grid consists mainly of shorter transmission circuits, which are less vulnerable to damage.[29][30]
The (nearly direct) currents induced in these lines from geomagnetic storms are harmful to electrical transmission equipment, especially transformers—inducing core saturation, constraining their performance (as well as tripping various safety devices), and causing coils and cores to heat up. In extreme cases, this heat can disable or destroy them, even inducing a chain reaction that can overload transformers.[31][32] Most generators are connected to the grid via transformers, isolating them from the induced currents on the grid, making them much less susceptible to damage due to geomagnetically induced current. However, a transformer that is subjected to this will act as an unbalanced load to the generator, causing negative sequence current in the stator and consequently rotor heating.
According to a study by Metatech corporation, a storm with a strength comparable to that of 1921 would destroy more than 300 transformers and leave over 130 million people without power in the United States, costing several trillion dollars.[33] The extent of the disruption is debated, with some congressional testimony indicating a potentially indefinite outage until transformers can be replaced or repaired.[34] These predictions are contradicted by a North American Electric Reliability Corporation report that concludes that a geomagnetic storm would cause temporary grid instability but no widespread destruction of high-voltage transformers. The report points out that the widely quoted Quebec grid collapse was not caused by overheating transformers but by the near-simultaneous tripping of seven relays.[35]
Besides the transformers being vulnerable to the effects of a geomagnetic storm, electricity companies can also be affected indirectly by the geomagnetic storm. For instance, internet service providers may go down during geomagnetic storms (and/or remain non-operational long after). Electricity companies may have equipment requiring a working internet connection to function, so during the period the internet service provider is down, the electricity too may not be distributed.[36]
By receiving geomagnetic storm alerts and warnings (e.g. by the Space Weather Prediction Center; via Space Weather satellites as SOHO or ACE), power companies can minimize damage to power transmission equipment, by momentarily disconnecting transformers or by inducing temporary blackouts. Preventive measures also exist, including preventing the inflow of GICs into the grid through the neutral-to-ground connection.[29]
Communications[edit]
High frequency (3–30 MHz) communication systems use the ionosphere to reflect radio signals over long distances. Ionospheric storms can affect radio communication at all latitudes. Some 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.
Military detection or early warning systems operating in the high frequency range are also affected by solar activity. The over-the-horizon radar bounces signals off the ionosphere to monitor the launch of aircraft and missiles from long distances. During geomagnetic storms, this system can be severely hampered by radio clutter. Also 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 avoid unnecessary maintenance. When an aircraft and a ground station are aligned with the Sun, high levels of noise can occur on air-control radio frequencies. This can also happen on UHF and SHF satellite communications, when an Earth station, a satellite and the Sun are in alignment. In order to prevent unnecessary maintenance on satellite communications systems aboard aircraft AirSatOne provides a live feed for geophysical events from NOAA's Space Weather Prediction Center.[37] allows users to view observed and predicted space storms. Geophysical Alerts are important to flight crews and maintenance personnel to determine if any upcoming activity or history has or will have an effect on satellite communications, GPS navigation and HF Communications.
Telegraph lines in the past were affected by geomagnetic storms. Telegraphs used a single long wire for the data line, stretching for many miles, using the ground as the return wire and 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 diminished the signal, when subtracted from the battery polarity, or to overly strong and spurious signals when added to it; some operators 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 unless they are fiber optic.[38]
Damage to communications satellites can disrupt non-terrestrial telephone, television, radio and Internet links.[39] The National Academy of Sciences reported in 2008 on possible scenarios of widespread disruption in the 2012–2013 solar peak.[40] A solar superstorm could cause large-scale global months-long Internet outages. A study describes potential mitigation measures and exceptions – such as user-powered mesh networks, related peer-to-peer applications and new protocols – and analyzes the robustness of the current Internet infrastructure.[41][42][43]
[edit]
Global navigation satellite systems (GNSS), and other navigation systems such as LORAN 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 was inaccurate by as much as several miles. If navigators had been alerted that a proton event or geomagnetic storm was in progress, they could have switched to a backup system.
GNSS signals are affected when solar activity causes sudden variations in the density of the ionosphere, causing the satellite signals to scintillate (like a twinkling star). 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.
One technology used to allow GNSS receivers to continue to operate in the presence of some confusing signals is Receiver Autonomous Integrity Monitoring (RAIM), used by GPS. However, RAIM is predicated on the assumption that a majority of the GPS constellation is operating properly, and so it is much less useful when the entire constellation is perturbed by global influences such as geomagnetic storms. Even if RAIM detects a loss of integrity in these cases, it may not be able to provide a useful, reliable signal.
Satellite hardware damage[edit]
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 1,000 km (600 mi) increases significantly. This results in increased drag, causing satellites to slow and change orbit slightly. Low Earth orbit satellites that are not repeatedly boosted to higher orbits slowly fall and eventually burn up. Skylab's 1979 destruction is an example of a spacecraft reentering Earth's atmosphere prematurely as a result of higher-than-expected solar activity.[44] During the great geomagnetic storm of March 1989, four of the U.S. 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 fell out of orbit in December the same year.[45]
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, due to the unusually weak geomagnetic field at low Earth orbit.[46]
Pipelines[edit]
Rapidly fluctuating geomagnetic fields can produce geomagnetically induced currents in pipelines. This can cause multiple problems for pipeline engineers. Pipeline flow meters can transmit erroneous flow information and the corrosion rate of the pipeline can be dramatically increased.[47][48]
Radiation hazards to humans[edit]
Earth's atmosphere and magnetosphere allow adequate protection at ground level, but astronauts are subject to potentially lethal radiation poisoning. The penetration of high-energy particles into living cells can cause chromosome damage, cancer and other health problems. Large doses can be immediately fatal. Solar protons with energies greater than 30 MeV are particularly hazardous.[49]
Solar proton events can also produce elevated radiation aboard aircraft flying at high altitudes. Although these risks are small, flight crews may be exposed repeatedly, and monitoring of solar proton events by satellite instrumentation allows exposure to be monitored and evaluated, and eventually flight paths and altitudes to be adjusted to lower the absorbed dose.[50][51][52]
Ground level enhancements, also known as ground level events or GLEs, occur when a solar particle event contains particles with sufficient energy to have effects at ground level, mainly detected as an increase in the number of neutrons measured at ground level. These events have been shown to have an impact on radiation dosage, but they do not significantly increase the risk of cancer.[53]
Effect on animals[edit]
There is a large but controversial body of scientific literature on connections between geomagnetic storms and human health. This began with Russian papers, and the subject was subsequently studied by Western scientists. Theories for the cause include the involvement of cryptochrome, melatonin, the pineal gland, and the circadian rhythm.[54]
Some scientists suggest that solar storms induce whales to beach themselves.[55][56] Some have speculated that migrating animals which use magnetoreception to navigate, such as birds and honey bees, might also be affected.[57]
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