Solar flare

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Solar_flare

An X5.4-class solar flare causing blooming, vertical streaking, and diffraction patterns to form in the image taken by the 131 Å (13.1 nm) sensor aboard the Solar Dynamics Observatory on 6 March 2012

 

A solar flare is an intense localized eruption of electromagnetic radiation in the Sun's atmosphere. Flares occur in active regions and are often, but not always, accompanied by coronal mass ejections, solar particle events, and other solar phenomena. The occurrence of solar flares varies with the 11-year solar cycle.

Solar flares are thought to occur when stored magnetic energy in the Sun's atmosphere accelerates charged particles in the surrounding plasma. This results in the emission of electromagnetic radiation across the electromagnetic spectrum.

High-energy electromagnetic radiation from solar flares is absorbed by the daylight side of Earth's upper atmosphere, in particular the ionosphere, and does not reach the surface. This absorption can temporarily increase the ionization of the ionosphere which may interfere with short-wave radio communication. The prediction of solar flares is an active area of research.

Flares also occur on other stars, where the term stellar flare applies.

Description

Solar flares are eruptions of electromagnetic radiation originating in the Sun's atmosphere. They affect all layers of the solar atmosphere (photosphere, chromosphere, and corona). The plasma medium is heated to >10⁷ kelvin, while electrons, protons, and heavier ions are accelerated to near the speed of light. Flares emit electromagnetic radiation across the electromagnetic spectrum at all wavelengths, from radio waves to gamma rays.

Flares occur in active regions, often around sunspots, where intense magnetic fields penetrate the photosphere to link the corona to the solar interior. Flares are powered by the sudden (timescales of minutes to tens of minutes) release of magnetic energy stored in the corona. The same energy releases may also produce coronal mass ejections (CMEs), although the relationship between CMEs and flares is still not well understood.

Solar flares occur in a power-law spectrum of magnitudes; an energy release of typically 10²⁰ joules of energy suffices to produce a clearly observable event, while a major event can emit up to 10²⁵ joules.

Associated with solar flares are flare sprays. They involve faster ejections of material than eruptive prominences, and reach velocities of 20 to 2000 kilometers per second.

Frequency

The frequency of occurrence of solar flares varies with the 11-year solar cycle. It can range from several per day during solar maximum to less than one every week during solar minimum. Additionally, more powerful flares are less frequent than weaker ones. For example, X10-class (severe) flares occur on average about eight times per cycle, whereas M1-class (minor) flares occur on average about 2000 times per cycle.

Erich Rieger discovered with coworkers in 1984 an approximately 154 day period in the occurrence of gamma-ray emitting solar flares at least since the solar cycle 19. The period has since been confirmed in most heliophysics data and the interplanetary magnetic field and is commonly known as the Rieger period. The period's resonance harmonics also have been reported from most data types in the heliosphere.

Duration

The duration of a solar flare depends heavily on the wavelength of the electromagnetic radiation used in its calculation. This is due to different wavelengths being emitted through different processes and at different heights in the Sun's atmosphere.

A common measure of flare duration is the full width at half maximum (FWHM) time of soft X-ray flux within the wavelength bands 0.05 to 0.4 and 0.1 to 0.8 nanometres (0.5 to 4 and 1 to 8 ångströms) measured by the GOES spacecraft in geosynchronous orbit. The FWHM time spans from when a flare's flux first reaches halfway between its maximum flux and the background flux and when it again reaches this value as the flare decays. Using this measure, the duration of a flare ranges from approximately tens of seconds to several hours with a median duration of approximately 6 and 11 minutes in the 0.05 to 0.4 and 0.1 to 0.8 nanometre bands, respectively.

Post-eruption loops and arcades

See also: Coronal loop

A post-eruption arcade present after an X5.7-class solar flare during the Bastille Day solar storm.

After the eruption of a solar flare, post-eruption loops made up of hot plasma begin to form across the neutral line separating regions of opposite magnetic polarity near the flare's source. These loops extend from the photosphere up into the corona and form along the neutral line at increasingly greater distances from the source as time progresses. The existence of these hot loops is thought to be continued by prolonged heating present after the eruption and during the flare's decay stage.

In sufficiently powerful flares, typically of C-class or higher, the loops may combine to form an elongated arch-like structure known as a post-eruption arcade. These structures may last anywhere from multiple hours to multiple days after the initial flare. In some cases, dark sunward-traveling plasma voids known as supra-arcade downflows may form above these arcades.

Cause

Flares occur when accelerated charged particles, mainly electrons, interact with the plasma medium. Evidence suggests that the phenomenon of magnetic reconnection leads to this extreme acceleration of charged particles. On the Sun, magnetic reconnection may happen on solar arcades – a series of closely occurring loops following magnetic lines of force. These lines of force quickly reconnect into a lower arcade of loops leaving a helix of magnetic field unconnected to the rest of the arcade. The sudden release of energy in this reconnection is the origin of the particle acceleration. The unconnected magnetic helical field and the material that it contains may violently expand outwards forming a coronal mass ejection. This also explains why solar flares typically erupt from active regions on the Sun where magnetic fields are much stronger.

Although there is a general agreement on the source of a flare's energy, the mechanisms involved are still not well understood. It is not clear how the magnetic energy is transformed into the kinetic energy of the particles, nor is it known how some particles can be accelerated to the GeV range (10⁹ electron volt) and beyond. There are also some inconsistencies regarding the total number of accelerated particles, which sometimes seems to be greater than the total number in the coronal loop. Scientists are unable to forecast flares.

Classification

Soft X-ray

The modern classification system for solar flares uses the letters A, B, C, M, or X, according to the peak flux in watts per square metre (W/m²) of soft X-rays with wavelengths 0.1 to 0.8 nanometres (1 to 8 ångströms), as measured by the GOES spacecraft in geosynchronous orbit.

Classification	Peak flux range (W/m2)
A	< 10−7
B	10−7 – 10−6
C	10−6 – 10−5
M	10−5 – 10−4
X	> 10−4

The strength of an event within a class is noted by a numerical suffix ranging from 1 up to, but excluding, 10, which is also the factor for that event within the class. Hence, an X2 flare is twice the strength of an X1 flare, an X3 flare is three times as powerful as an X1, and only 50% more powerful than an X2. An X2 is four times more powerful than an M5 flare. X-class flares with a peak flux that exceeds 10⁻³ W/m² may be noted with a numerical suffix equal to or greater than 10.

This system was originally devised in 1970 and included only the letters C, M, and X. These letters were chosen to avoid confusion with other optical classification systems. The A and B classes would later be added in the 1990s as instruments became more sensitive to weaker flares. Around the same time, the backronym moderate for M-class flares and extreme for X-class flares began to be used.

H-alpha

An earlier flare classification was based on H-alpha spectral observations. The scheme uses both the intensity and emitting surface. The classification in intensity is qualitative, referring to the flares as: faint (f), normal (n), or brilliant (b). The emitting surface is measured in terms of millionths of the hemisphere and is described below. (The total hemisphere area A_H = 15.5 × 10¹² km².)

Classification	Corrected area (millionths of hemisphere)
S	< 100
1	100–250
2	250–600
3	600–1200
4	> 1200

A flare then is classified taking S or a number that represents its size and a letter that represents its peak intensity, v.g.: Sn is a normal sunflare.

Duration

Solar flares can also be classified based on their duration as either impulsive or long duration events (LDE). The time threshold separating the two is not well defined. The SWPC regards events requiring 30 minutes or more to decay to half maximum as LDEs, whereas Belgium's Solar-Terrestrial Centre of Excellence regards events with duration greater than 60 minutes as LDEs.

Effects

Terrestrial

X-rays and extreme ultraviolet radiation emitted by solar flares are absorbed by the daylight side of Earth's atmosphere and do not reach the Earth's surface. Therefore, solar flares pose no direct danger to humans on Earth. However, this absorption of high-energy electromagnetic radiation can temporarily increase the ionization of the upper atmosphere, which can interfere with short-wave radio communication, and can temporarily heat and expand the Earth's outer atmosphere. This expansion can increase drag on satellites in low Earth orbit, which can lead to orbital decay over time.

Radio blackouts

Further information: Sudden ionospheric disturbance

See also: Communications blackout § Space weather

The temporary increase in ionization of the daylight side of Earth's atmosphere, in particular the D layer of the ionosphere, can interfere with short-wave radio communications that rely on its level of ionization for skywave propagation. Skywave, or skip, refers to the propagation of radio waves reflected or refracted off of the ionized ionosphere. When ionization is higher than normal, radio waves get degraded or completely absorbed by losing energy from the more frequent collisions with free electrons.

The level of ionization of the atmosphere correlates with the strength of the associated solar flare in soft X-ray radiation. The NOAA classifies radio blackouts by the peak soft X-ray intensity of the associated flare.

Classification	Associated solar flare	Description
R1	M1	Minor radio blackout
R2	M5	Moderate radio blackout
R3	X1	Strong radio blackout
R4	X10	Severe radio blackout
R5	X20	Extreme radio blackout

Magnetic crochet

The increased ionization of the D and E layers of the ionosphere caused by large solar flares increases the electrical conductivity of these layers allowing for the flow of electric currents. These ionospheric currents induce a magnetic field which can be measured by ground-based magnetometers. This phenomenon is known as a magnetic crochet or solar flare effect (SFE). The former name derives from its appearance on magnetometers resembling a crochet hook. These disturbances are on the order of a few nanoTeslas, which is relatively minor compared to those induced by geomagnetic storms.

In space

For astronauts in low earth orbit an expected radiation dose from the electromagnetic radiation emitted during a solar flare is about 0.05 gray, which is not immediately lethal on its own. Of much more concern for astronauts is the particle radiation associated with solar particle events.

Observations

Further information: Solar observation

Flares produce radiation across the electromagnetic spectrum, although with different intensity. They are not very intense in visible light, but they can be very bright at particular spectral lines. They normally produce bremsstrahlung in X-rays and synchrotron radiation in radio.

History

Optical observations

Richard Carrington's sketch of the first recorded solar flare (A and B mark the initial bright points which moved over the course of five minutes to C and D before disappearing)

Solar flares were first observed by Richard Carrington and Richard Hodgson independently on 1 September 1859 by projecting the image of the solar disk produced by an optical telescope through a broad-band filter. It was an extraordinarily intense white light flare, a flare emitting a high amount of light in the visual spectrum.

Since flares produce copious amounts of radiation at H-alpha, adding a narrow (≈1 Å) passband filter centered at this wavelength to the optical telescope allows the observation of not very bright flares with small telescopes. For years Hα was the main, if not the only, source of information about solar flares. Other passband filters are also used.

Radio observations

Further information: Solar radio emission

During World War II, on February 25 and 26, 1942, British radar operators observed radiation that Stanley Hey interpreted as solar emission. Their discovery did not go public until the end of the conflict. The same year Southworth also observed the Sun in radio, but as with Hey, his observations were only known after 1945. In 1943, Grote Reber was the first to report radioastronomical observations of the Sun at 160 MHz. The fast development of radioastronomy revealed new peculiarities of the solar activity like storms and bursts related to the flares. Today ground-based radiotelescopes observe the Sun from c. 15 MHz up to 400 GHz.

Space telescopes

Because the Earth's atmosphere absorbs much of the electromagnetic radiation emitted by the Sun with wavelengths shorter than 300 nm, space-based telescopes allowed for the observation of solar flares in previously unobserved high-energy spectral lines. Since the 1970s, the GOES series of satellites have been continuously observing the Sun in soft X-rays, and their observations have become the standard measure of flares, diminishing the importance of the H-alpha classification. Additionally, space-based telescopes allow for the observation of extremely long wavelengths—as long as a few kilometres—which cannot propagate through the ionosphere.

Examples of large solar flares

See also: List of solar storms

Space weather—March 2012.

The most powerful flare ever observed is thought to be the flare associated with the 1859 Carrington Event. While no soft X-ray measurements were made at the time, the magnetic crochet associated with the flare was recorded by ground-based magnetometers allowing the flare's strength to be estimated after the event. Using these magnetometer readings, its soft X-ray class has been estimated to be greater than X10. The soft X-ray class of the flare has also been estimated to be around X50.

In modern times, the largest solar flare measured with instruments occurred on 4 November 2003. This event saturated the GOES detectors, and because of this its classification is only approximate. Initially, extrapolating the GOES curve, it was estimated to be X28. Later analysis of the ionospheric effects suggested increasing this estimate to X45. This event produced the first clear evidence of a new spectral component above 100 GHz.

Other large solar flares also occurred on 2 April 2001 (X20+), 28 October 2003 (X17.2+ and 10), 7 September 2005 (X17), 9 August 2011 (X6.9), 7 March 2012 (X5.4), and 6 September 2017 (X9.3).

Prediction

Current methods of flare prediction are problematic, and there is no certain indication that an active region on the Sun will produce a flare. However, many properties of sunspots and active regions correlate with flaring. For example, magnetically complex regions (based on line-of-sight magnetic field) called delta spots produce the largest flares. A simple scheme of sunspot classification due to McIntosh, or related to fractal complexity is commonly used as a starting point for flare prediction. Predictions are usually stated in terms of probabilities for occurrence of flares above M- or X-class within 24 or 48 hours. The U.S. National Oceanic and Atmospheric Administration (NOAA) issues forecasts of this kind. MAG4 was developed at the University of Alabama in Huntsville with support from the Space Radiation Analysis Group at Johnson Space Flight Center (NASA/SRAG) for forecasting M- and X-class flares, CMEs, fast CME, and Solar Energetic Particle events. A physics-based method that can predict imminent large solar flares was proposed by Institute for Space-Earth Environmental Research (ISEE), Nagoya University.

In popular culture

See also: Sun in culture and Sun in fiction

A solar flare has been the main plot device for science fiction stories:

• Flare, a 1992 novel by Roger Zelazny and Thomas Thurston Thomas
• Inconstant Moon, a 1996 Outer Limits episode on Showtime by writer Larry Niven and starring Michael Gross and Joanna Gleason
• Tamizhuku En Ondrai Azhuthavum, a 2015 Tamil language film directed by Ramprakash Rayappa and starring Nakul
• Every Little Thing, the season two premiere of the a 2019 Apple TV+ series For All Mankind created by Ronald D. Moore, Matt Wolpert and Ben Nedivi
• Finch, a 2021 Apple TV+ film directed by Miguel Sapochnik and starring Tom Hanks
• Stowaway, a 2021 science-fiction thriller film by Joe Penna and Ryan Morrison
• COBRA, a 2020 British TV series in which a huge flare strikes Europe, damaging the UK's power grid and navigation systems, starring Robert Carlyle and Victoria Hamilton
• Perry, a 2003 episode of Smallville in which solar flares cause Clark Kent to be unable to control his powers
• The Maze Runner, a series of young adult dystopian science fiction novels written by James Dashner

They are also a popular doomsday scenario in disaster films, where their effects on Earth are often greatly exaggerated.

Security

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Security

Women's Army Corps (1941–1945) associated national security with avoiding conversations about war work.

Security is protection from, or resilience against, potential harm (or other unwanted coercion) caused by others, by restraining the freedom of others to act. Beneficiaries (technically referents) of security may be of persons and social groups, objects and institutions, ecosystems or any other entity or phenomenon vulnerable to unwanted change.

Refugees fleeing war and insecurity in Iraq and Syria arrive at Lesbos Island, supported by Spanish volunteers, 2015

Security mostly refers to protection from hostile forces, but it has a wide range of other senses: for example, as the absence of harm (e.g. freedom from want); as the presence of an essential good (e.g. food security); as resilience against potential damage or harm (e.g. secure foundations); as secrecy (e.g. a secure telephone line); as containment (e.g. a secure room or cell); and as a state of mind (e.g. emotional security).

The term is also used to refer to acts and systems whose purpose may be to provide security (security company, security police, security forces, security service, security agency, security guard, cyber security systems, security cameras, remote guarding). Security can be physical and virtual.

Etymology

The word 'secure' entered the English language in the 16th century. It is derived from Latin securus, meaning freedom from anxiety: se (without) + cura (care, anxiety).

Overview

Referent

A security referent is the focus of a security policy or discourse; for example, a referent may be a potential beneficiary (or victim) of a security policy or system.

Security referents may be persons or social groups, objects, institutions, ecosystems, or any other phenomenon vulnerable to unwanted change by the forces of its environment. The referent in question may combine many referents, in the same way that, for example, a nation state is composed of many individual citizens.

Context

The security context is the relationships between a security referent and its environment. From this perspective, security and insecurity depend first on whether the environment is beneficial or hostile to the referent, and also how capable is the referent of responding to its/their environment in order to survive and thrive.

Capabilities

The means by which a referent provides for security (or is provided for) vary widely. They include, for example:

• Coercive capabilities, including the capacity to project coercive power into the environment (e.g. aircraft carrier, handgun, firearms);
• Protective systems (e.g. lock, fence, wall, antivirus software, air defence system, armour)
• Warning systems (e.g. alarm, radar)
• Diplomatic and social action intended to prevent insecurity from developing (e.g. conflict prevention and transformation strategies); and
• Policy intended to develop the lasting economic, physical, ecological and other conditions of security (e.g. economic reform, ecological protection, progressive demilitarization, militarization).

Effects

Any action intended to provide security may have multiple effects. For example, an action may have wide benefit, enhancing security for several or all security referents in the context; alternatively, the action may be effective only temporarily, or benefit one referent at the expense of another, or be entirely ineffective or counterproductive.

Contested approaches

Approaches to security are contested and the subject of debate. For example, in debate about national security strategies, some argue that security depends principally on developing protective and coercive capabilities in order to protect the security referent in a hostile environment (and potentially to project that power into its environment, and dominate it to the point of strategic supremacy). Others argue that security depends principally on building the conditions in which equitable relationships can develop, partly by reducing antagonism between actors, ensuring that fundamental needs can be met, and also that differences of interest can be negotiated effectively.

U.S. Customs and Border Protection vehicle at the Canada–United States border

Contexts of security (examples)

The table shows some of the main domains where security concerns are prominent.

IT realm Application security Communications security Computer security Data security Digital security Endpoint security Information security Internet security Network security Usable Security

Physical realm Airport security Corporate security Food security Environmental security Home security Infrastructure security Physical security Port security/Supply chain security Security bag Security print Border security Security seal

Political National security Public security Homeland security Internal security International security Human security Monetary Economic security/financial security Social security

The range of security contexts is illustrated by the following examples (in alphabetical order):

Computer security

Main article: Computer security

Computer security, also known as cybersecurity or IT security, refers to the security of computing devices such as computers and smartphones, as well as computer networks such as private and public networks, and the Internet. The field has growing importance due to the increasing reliance on computer systems in most societies. It concerns the protection of hardware, software, data, people, and also the procedures by which systems are accessed. The means of computer security include the physical security of systems and security of information held on them.

Corporate security

Main article: Corporate security

Corporate security refers to the resilience of corporations against espionage, theft, damage, and other threats. The security of corporations has become more complex as reliance on IT systems has increased, and their physical presence has become more highly distributed across several countries, including environments that are, or may rapidly become, hostile to them.

Security checkpoint at the entrance to the Delta Air Lines corporate headquarters in Atlanta

X-ray machines and metal detectors are used to control what is allowed to pass through an airport security perimeter.

Security checkpoint at the entrance to a shopping mall in Jakarta, Indonesia

Environmental security

Main article: Environmental security

Environmental security, also known as ecological security, refers to the integrity of ecosystems and the biosphere, particularly in relation to their capacity to sustain a diversity of life-forms (including human life). The security of ecosystems has attracted greater attention as the impact of ecological damage by humans has grown.

Graffiti about environmental security, Belarus, 2016

Food security

Main article: Food security

Food security refers to the ready supply of, and access to, safe and nutritious food. Food security is gaining in importance as the world's population has grown and productive land has diminished through overuse and climate change.

Climate change is affecting global agriculture and food security

Home security

Main article: Home security

Home security normally refers to the security systems used on a property used as a dwelling (commonly including doors, locks, alarm systems, lighting, fencing); and personal security practices (such as ensuring doors are locked, alarms activated, windows closed etc.)

Security spikes on the wall of a gated community in the East End of London

Human security

Main article: Human security

Youth play among the bombed ruins of Gaza City, 2009

Human security is an emerging paradigm which, in response to traditional emphasis on the right of nation states to protect themselves, has focused on the primacy of the security of people (individuals and communities). The concept is supported by the United Nations General Assembly, which has stressed "the right of people to live in freedom and dignity" and recognized "that all individuals, in particular vulnerable people, are entitled to freedom from fear and freedom from want".

National security

Main article: National security

National security refers to the security of a nation state, including its people, economy, and institutions. In practice, state governments rely on a wide range of means, including diplomacy, economic power, and military capabilities.

Perceptions of security

Since it is not possible to know with precision the extent to which something is 'secure' (and a measure of vulnerability is unavoidable), perceptions of security vary, often greatly. For example, a fear of death by earthquake is common in the United States (US), but slipping on the bathroom floor kills more people; and in France, the United Kingdom and the US there are far fewer deaths caused by terrorism than there are women killed by their partners in the home.

Another problem of perception is the common assumption that the mere presence of a security system (such as armed forces, or antivirus software) implies security. For example, two computer security programs installed on the same device can prevent each other from working properly, while the user assumes that he or she benefits from twice the protection that only one program would afford.

Security theater is a critical term for measures that change perceptions of security without necessarily affecting security itself. For example, visual signs of security protections, such as a home that advertises its alarm system, may deter an intruder, whether or not the system functions properly. Similarly, the increased presence of military personnel on the streets of a city after a terrorist attack may help to reassure the public, whether or not it diminishes the risk of further attacks.

Security concepts (examples)

Certain concepts recur throughout different fields of security:

• Access control – the selective restriction of access to a place or other resource.
• Assurance – an expression of confidence that a security measure will perform as expected.
• Authorization – the function of specifying access rights/privileges to resources related to information security and computer security in general and to access control in particular.
• Cipher – an algorithm that defines a set of steps to encrypt or decrypt information so that it is incomprehensible.
• Countermeasure – a means of preventing an act or system from having its intended effect.
• Defense in depth – a school of thought holding that a wider range of security measures will enhance security.
• Exploit (noun) – a means of capitalizing on a vulnerability in a security system (usually a cyber-security system).
• Identity management – enables the right individuals to access the right resources at the right times and for the right reasons.
• Password – secret data, typically a string of characters, usually used to confirm a user's identity.
• Resilience – the degree to which a person, community, nation or system is able to resist adverse external forces.
• Risk – a possible event which could lead to damage, harm, or loss.
• Security management – identification of an organization's assets (including people, buildings, machines, systems and information assets), followed by the development, documentation, and implementation of policies and procedures for protecting these assets.
• Threat – a potential source of harm.
• Vulnerability – the degree to which something may be changed (usually in an unwanted manner) by external forces.

Ionospheric storm

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Ionospheric_storm

Ionospheric storms are storms which contain varying densities of energised electrons in the ionosphere as produced from the sun. Ionospheric storms are caused by geomagnetic storms. They are categorised into positive and negative storms, where positive storms have a high density of electrons and negative storms contain a lower density. The total electron content (TEC) is used to measure these densities, and is a key variable used in data to record and compare the intensities of ionospheric storms.

Ionospheric storm occurrences are strongly linked with sudden increases of solar wind speed, where solar wind brings energised electrons into the upper atmosphere of the Earth and contributes to increased TEC. Larger storms form global visibility of auroras. Auroras are most commonly seen in the arctic circle; however, large ionospheric storms allow for them to be visible in places such as the United States, United Kingdom, and Europe. The most intense ionospheric storm occurred in 1859, commonly named the “solar storm of 1859” or the “Carrington Event.” The Carrington Event was named after Richard Carrington, an English astronomer who observed the irregular sun activity that occurred during the Carrington Event. The intensity of the storm brought the visibility of the aurora even closer to the equator, reported to be seen in places near it such as Florida and the Caribbean. Ionospheric storms can happen at any time and location.

X-Ray image of Aurora Borealis taken during an ionospheric storm by NASA.

F-region and D-region ionospheric storms are also considered main categories of ionospheric storms. The F-region storms occur due to sudden increases of energised electrons instilled into Earth's ionosphere. The F-region is the highest region of the ionosphere. Consisting of the F1 and F2 layers, its distance above the earth's surface is approximately 200–500 km. The duration of these storms are around a day and reoccur every approximately 27.3 days. Most ionospheric abnormalities occur in the F2 and E layers of the ionosphere. D-region storms occur immediately after F-region storms, and are referred to as the “Post-Storm Effect," the duration of it spanning for a week after the F-region storm's occurrence.

Historical occurrences

The largest ionospheric storm occurred during the Carrington event on August 28, 1859 and caused extensive damages to various parts including the sparking of fires in railway signals and telegraph wires. The substantial density of energised electrons produced by the storm caused these electrical overloads and shortages.

Occurrences of storms in the last 35 years have been consolidated and measured in maximum Ap which records the average daily geomagnetic activity during ionospheric storms. There are higher levels of geomagnetic activity with high maximum Ap counts. Ap counts in terms of geomagnetic activity from 0-7 are considered "quiet," 8-15 "unsettled," 16-29 "active," 30-49 "minor storm," 50-99 "major storm," and above 100 classified as a "severe storm." Minor storms in the last 35 years ranging from 30-49 Ap occurred on 13 September 1999 (46), 11 October 2008 (34), 11 March 2011 (37), 9 October 2012 (46) and on 19 February 2014 (43). Major storms ranging from 50-99 Ap occurred on 6 April 2000 (82), 7 April 2000 (74), 11 April 2001 (85), 18 April 2002 (63), 20 April 2002 (70), 22 January 2004 (64), 18 January 2005 (84), 5 April 2010 (55), 9 March 2012 (87), 15 July 2012 (78) and on 1 June 2013 (58). Severe storms equalling or exceeding 100 Ap occurred on 8 February 1986 (202), 9 February 1986 (100), 13 March 1989 (246), 14 March 1989 (158), 17 November 1989 (109), 10 April 1990 (124), 7 April 1995 (100), 31 March 2001 (192), 6 November 2001 (142), 18 August 2003 (108), 29 October 2003 (204), 30 October 2003 (191), 20 November 2003 (150), 27 July 2004 (186), 8 November 2004 (140) and on 10 November 2004 (161).

In recent accounts, the St Patrick's day storm in March 2013 and 2015 caused a strong negative phase in the F2 ionospheric region. The March 2013 and 2015 storms were also long lasting, spanning for over 6 hours. The June 2015 Southern Hemisphere winter storm had a shorter duration, lasting between 4 and 6 hours, and producing a positive effect in the ionosphere. It is difficult to determine the exact location and time for the occurrences of ionospheric storms, its effects being dependent on season, their varying starting points, compositional changes in the ionosphere and the travelling ionospheric disturbances (TIDs) in relation to gravity waves having varying impacts on different locations.

Phases of ionospheric storms

In the commencement of an ionospheric storm, due to geomagnetic disturbances in the ionosphere, the storm will become positive for a brief duration. Then, it will become a negative phase storm, and revert to a recovery phase where electron density neutralises.

Positive phase

The positive phase of an ionospheric storm will last for around the first 24 hours. In this phase, electron density in the ionosphere, particularly in higher altitude layers such as F1 and F2 will increase. Ionisation in the positive phase will be less apparent due to the increase of electron density. Positive phase ionospheric storms have a longer duration and are more prevalent in winter. During the positive phase of large ionospheric storms, the altitude of ionospheric F-region increases, resulting in the massive tongue-shaped plasma anomaly spreading anti-sunward over the polar cap, which can be observed by ground radars, as well as by satellites and the GPS system. Even for the largest geomagnetic storms, such as the 20 November 2003 superstorm, modern general circulation models are able to simulate positive ionospheric anomalies.

Negative phase

The negative phase of an ionospheric storm will occur directly after the storm's positive phase and last one to two days after the positive phase decreases in electron density to "below its quiet time reference level." Negative phases decrease the electron density of the storm. They also span for longer durations and appear more often during summer.

Recovery phase

The recovery phase of the ionospheric storm occurs after the negative phase ends, and neutralises the electron density. A time scale of 12 hours to 1 day can be used in accordance with the Thermosphere Ionosphere General Circulation Model (TIGCM) as a means of calculating the precise time of electron density restabilising post-storm.

Effects on ionospheric layers

The effects of ionospheric storms on different layers in the ionosphere including in the F-region, E-region and D-region vary depending on the magnitude of the storm. F-Region is the most affected layer due to it ranging the highest altitude compared to the E-region and D-region. The D-region is the region with the lowest altitude and will receive the least geomagnetic disturbance.

F-region

The F-region is the highest layer of the ionosphere and inner atmosphere, around 200 km above Earth's surface and spanning around 300 km in total layer altitude.The F2-region of the F-region (highest altitude inner atmospheric layer) will be affected through the decrease of critical frequency and maximum usable frequency, which is necessary for high frequency radio communication. The F-region is affected by the friction of solar wind on the ionospheric boundaries which causes magnetospheric motion that may infiltrate into the ionosphere or exit it, creating disturbances which increase and decrease TEC and electron density. During ionospheric storms, it is more common for "anomalous" increases and decreases of TEC and electron density to occur in the F2-layer. Ionisation density is also affected in the F-region, decreasing as the height increases, and as ionisation density increases, atoms lose electrons and therefore lower altitudes lose electron density. The lower layers of the F-region such as the F1-layer have higher amounts of ionisation and less electron density.

E-region

The E-region is the middle layer of the ionosphere, approximately 100 km above the Earth's surface, spanning around 100 km up. Effects on the E-region are mainly associated with the high latitudes of the layer, where more severe geomagnetic disturbances occur. Ionisation in this layer is predominantly derived from the particle precipitation in auroras. Due to its lower latitude, there is greater ionisation density compared to that of the F-region, and less electron density. Increased conductivity of currents is caused by the convection electric fields of the magnetosphere that run down the lines of the magnetic field in the E-region. The increased conductivity is also from the effects of the ionospheric storm. There is also a maximisation in the E-region of the transfer of energy from plasma to neutral particles which promotes "frictional heating" and is used as a heat source for the thermosphere.

D-region

The D-region is the lowest layer of the ionosphere, approximately 60 km above the Earth's surface and its layer's altitude spanning around 30–40 km. The top of the D-region is around 90–100 km above the Earth's surface. When ionospheric storms occur, there is enhanced ionisation of electrons that happens in the D-region and causes a decline in day-night asymmetry (DLPT depth.) DLPT depth is calculated by subtracting average day rate by average night rate and dividing it by the average of the rates. The DLPT depth decreases as Ap increases in the D-layer.

Impacts

Radio communications

There are strong disturbances to radio communications in the event of an ionospheric storm, where in middle and high altitudes, radio communications are considered “ineffective.” This is due to radio waves being found in the ionosphere where the sudden increase of solar wind and energised electrons will interfere. The impacts of disturbances related to radio communications can include temporary blackouts of signal to radio-wave based technology such as televisions, radios and cordless phones. Global impacts vary, including the detriment of digital broadcasting and the displaying of information through radio-communication technologies which may temporarily eliminate the use of certain technologies.

Aircraft and electrical systems

Aircraft passengers and the crew are more prone to dangerous exposure from radiation during an ionospheric storm. Flight altitudes are usually 10 km or more, so when an ionospheric storm occurs during the flight, people on the plane will potentially gain an approximate 0.1% chance of developing a lethal cancer during their lifetime. The plane when flying at a 10 km or above altitude will have around 300 times more exposure to ionised radiation than on sea level. The energised particles produced by the ionospheric storm will also potentially cause damage and disrupt "microelectronic circuitry" due to single event effect (SEE), when the energised particles interconnect with the semiconductor device and causes system failure. Aircrew and the pilot in this situation during short circuiting of aircraft electrical equipment will be reprioritised of their work and cause detriment to the overall safety and wellbeing of the passengers.

Satellites

Ionospheric storms have a visible effect on satellites and satellite communication. Solar cells on satellites will have a chance of being affected or destroyed and this will lead to disturbances in satellite communications and signals commonly used for various technologies. This disturbance can hinder the sending of signals such as in the form of broadcasting and data communications.

Climate

Earthward solar winds and excessive radiation produced from it has limited effect on the climate. The radiation emitted by solar wind only reaches the highest layers of the Earth's atmosphere, including the ionosphere. In the lower atmospheres, where climate change is able to be recorded and monitored, there are minimal trends supporting an ionospheric storm's impact. It is recorded that the increase of solar wind during March 2012 in the United States “coincided” with the heat waves that occurred at the time. The impact on climate in accordance with ionospheric storms based on modern technology is shown to have little to no impact.

GPS and GNSS systems

Due to the disturbances of signals in the ionosphere caused by ionospheric storms, GPS systems are drastically affected. In the late 20th and 21st centuries GPS signals are incorporated within various phones, so the commonality of its use has greatly increased since its release. It is a significant piece of technology that is almost entirely affected as it serves the purpose of displaying direction, which can prevent people from being able to tell directions. Directional equipment like Global Navigation Satellite Services (GNSS) is also used in aircraft. This system can be compromised by radiation damage on satellites and solar cells all of which are needed for this navigation system to work. When aircraft loses access to GNSS in the event of an ionospheric storm, back up aircraft procedures are available.

Storm detection technology

During the Carrington Event in 1859 where there were only a limited number of available measuring technologies, the full extent of the impacts could not be precisely recorded apart from recounts in newspaper articles written in 1859. In the late 20th and early 21st century, forecasting technology has been improved. This technology allows meteorologists to detect the highest frequency that can be vertically returned  24 hours in advance with accuracy of 8-13% periods with limited disturbance. PropMan, created by K. Davies in the early 1970s is a program which contains the ionospheric prediction code (IONSTORM), for the purpose of forecasting maximum usable frequencies (MUFs) during ionospheric storms when F-region communication frequencies are negated.

Geomagnetic storm

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Geomagnetic_storm

Artist's depiction of solar wind particles interacting with Earth's magnetosphere. Sizes are not to scale.

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 and/or cloud of magnetic field that interacts with the Earth's magnetic field.

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. 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. In 1989, a geomagnetic storm energized ground induced currents that disrupted electric power distribution throughout most of Quebec and caused aurorae as far south as Texas.

Definition

A geomagnetic storm is defined by changes in the Dst (disturbance – storm time) index. The Dst index estimates the globally averaged change of the horizontal component of the Earth's magnetic field at the magnetic equator based on measurements from a few magnetometer stations. Dst is computed once per hour and reported in near-real-time. During quiet times, Dst is between +20 and −20 nano-Tesla (nT).

A geomagnetic storm has three phases: initial, main and recovery. The initial phase is characterized by Dst (or its one-minute component SYM-H) increasing by 20 to 50 nT in tens of minutes. The initial phase is also referred to as a storm sudden commencement (SSC). However, not all geomagnetic storms have an initial phase and not all sudden increases in Dst or SYM-H are followed by a geomagnetic storm. The main phase of a geomagnetic storm is defined by Dst decreasing to less than −50 nT. The selection of −50 nT to define a storm is somewhat arbitrary. The minimum value during a storm will be between −50 and approximately −600 nT. The duration of the main phase is typically 2–8 hours. The recovery phase is when Dst changes from its minimum value to its quiet time value. The recovery phase may last as short as 8 hours or as long as 7 days.

Aurora borealis

The size of a geomagnetic storm is classified as moderate (−50 nT > minimum of Dst > −100 nT), intense (−100 nT > minimum Dst > −250 nT) or super-storm (minimum of Dst < −250 nT).

Measuring intensity

Geomagnetic storm intensity is reported in several different ways, including:

• K-index
• A-index
• The G-scale used by the U.S. National Oceanic and Atmospheric Administration, which rates the storm from G1 to G5 (i.e. G1, G2, G3, G4, G5 in order), where G1 is the weakest storm classification (corresponding to a Kp value of 5), and G5 is the strongest (corresponding to a Kp value of 9).

History of the theory

In 1931, Sydney Chapman and Vincenzo C. A. Ferraro wrote an article, A New Theory of Magnetic Storms, that sought to explain the phenomenon. 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. 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.

Occurrences

Further information: List of solar storms

The first scientific observation of the effects of a geomagnetic storm occurred early in the 19th century: from May 1806 until June 1807, Alexander von Humboldt recorded the bearing of a magnetic compass in Berlin. On 21 December 1806, he noticed that his compass had become erratic during a bright auroral event.

On September 1–2, 1859, the largest recorded geomagnetic storm occurred. From August 28 until September 2, 1859, numerous sunspots and solar flares were observed on the Sun, with the largest flare on September 1. This is referred to as the Solar storm of 1859 or the Carrington Event. It can be assumed that a massive coronal mass ejection (CME) was launched from the Sun and reached the Earth within eighteen hours—a trip that normally takes three to four days. The horizontal field was reduced by 1600 nT as recorded by the Colaba Observatory. It is estimated that Dst would have been approximately −1760 nT. Telegraph wires in both the United States and Europe experienced induced voltage increases (emf), in some cases even delivering shocks to telegraph operators and igniting fires. Aurorae were seen as far south as Hawaii, Mexico, Cuba and Italy—phenomena that are usually only visible in polar regions. Ice cores show evidence that events of similar intensity recur at an average rate of approximately once per 500 years.

Since 1859, less severe storms have occurred, notably the aurora of November 17, 1882 and the May 1921 geomagnetic storm, both with disruption of telegraph service and initiation of fires, and 1960, when widespread radio disruption was reported.

GOES-7 monitors the space weather conditions during the Great Geomagnetic storm of March 1989, the Moscow neutron monitor recorded the passage of a CME as a drop in levels known as a Forbush decrease.

In early August 1972, a series of flares and solar storms peaks with a flare estimated around X20 producing the fastest CME transit ever recorded and a severe geomagnetic and proton storm that disrupted terrestrial electrical and communications networks, as well as satellites (at least one made permanently inoperative), and spontaneously detonated numerous U.S. Navy magnetic-influence sea mines in North Vietnam.

The March 1989 geomagnetic storm caused the collapse of the Hydro-Québec power grid in seconds as equipment protection relays tripped in a cascading sequence. Six million people were left without power for nine hours. The storm caused auroras as far south as Texas and Florida. The storm causing this event was the result of a coronal mass ejected from the Sun on March 9, 1989. The minimum Dst was −589 nT.

On July 14, 2000, an X5 class flare erupted (known as the Bastille Day event) and a coronal mass was launched directly at the Earth. A geomagnetic super storm occurred on July 15–17; the minimum of the Dst index was −301 nT. Despite the storm's strength, no power distribution failures were reported. The Bastille Day event was observed by Voyager 1 and Voyager 2, thus it is the farthest out in the Solar System that a solar storm has been observed.

Seventeen major flares erupted on the Sun between 19 October and 5 November 2003, including perhaps the most intense flare ever measured on the GOES XRS sensor—a huge X28 flare, resulting in an extreme radio blackout, on 4 November. These flares were associated with CME events that caused three geomagnetic storms between 29 October and 2 November, during which the second and third storms were initiated before the previous storm period had fully recovered. The minimum Dst values were −151, −353 and −383 nT. Another storm in this sequence occurred on 4–5 November with a minimum Dst of −69 nT. The last geomagnetic storm was weaker than the preceding storms, because the active region on the Sun had rotated beyond the meridian where the central portion CME created during the flare event passed to the side of the Earth. The whole sequence became known as the Halloween Solar Storm. The Wide Area Augmentation System (WAAS) operated by the Federal Aviation Administration (FAA) was offline for approximately 30 hours due to the storm. The Japanese ADEOS-2 satellite was severely damaged and the operation of many other satellites were interrupted due to the storm.

Interactions with planetary processes

Magnetosphere in the near-Earth space environment.

The solar wind also carries with it the Sun's magnetic field. 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 becomes unstable, fragments, and may even disappear. In the northern and southern pole regions of the Earth, auroras are observable.

Instruments

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:

• 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 fields 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 determine the electron density profile—up to its peak, past which radio waves no longer return. Radio sounders in low Earth orbit aboard the Canadian Alouette 1 (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).
• Particle detectors include a Geiger counter, as was used for the original observations of the Van Allen radiation belt. Scintillator detectors came later, and still later "channeltron" electron multipliers 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 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. 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. 

Geomagnetic storm effects

Disruption of electrical systems

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. Such sudden electrical blackouts may threaten food production.

Main electrical grid

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.

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. 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. The extent of the disruption is debated, with some congressional testimony indicating a potentially indefinite outage until transformers can be replaced or repaired. 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.

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.

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.

Communications

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.^{[citation needed]} 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. 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.

Damage to communications satellites can disrupt non-terrestrial telephone, television, radio and Internet links. The National Academy of Sciences reported in 2008 on possible scenarios of widespread disruption in the 2012–2013 solar peak. 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.

Navigation systems

The Global Navigation Satellite System (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 GPS receivers to continue to operate in the presence of some confusing signals is Receiver Autonomous Integrity Monitoring (RAIM). 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

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. 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.

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.

Pipelines

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.

Radiation hazards to humans

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.

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.

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.

Effect on animals

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.

Some scientists suggest that solar storms induce whales to beach themselves. Some have speculated that migrating animals which use magnetoreception to navigate, such as birds and honey bees, might also be affected.