A solar flare is an intense localized eruption of
electromagnetic radiation
In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic field, electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, inf ...
in the
Sun
The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
's
atmosphere
An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...
.
Flares occur in
active region
An active region is a temporary region in the Sun's atmosphere characterized by a strong and complex magnetic field. They are often associated with sunspots and are commonly the source of violent eruptions such as coronal mass ejections and solar ...
s and are often, but not always, accompanied by
coronal mass ejection
A coronal mass ejection (CME) is a significant release of plasma and accompanying magnetic field from the Sun's corona into the heliosphere. CMEs are often associated with solar flares and other forms of solar activity, but a broadly accept ...
s,
solar particle event
In solar physics, a solar particle event (SPE), also known as a solar energetic particle (SEP) event or solar radiation storm, is a solar phenomenon which occurs when particles emitted by the Sun, mostly protons, become accelerated either in th ...
s, and other
solar phenomena
Solar phenomena are natural phenomena which occur within the atmosphere of the Sun. These phenomena take many forms, including solar wind, radio wave flux, solar flares, coronal mass ejections, coronal heating and sunspots.
These phenomena a ...
. The occurrence of solar flares varies with the 11-year
solar cycle
The solar cycle, also known as the solar magnetic activity cycle, sunspot cycle, or Schwabe cycle, is a nearly periodic 11-year change in the Sun's activity measured in terms of variations in the number of observed sunspots on the Sun's surfa ...
.
Solar flares are thought to occur when stored
magnetic energy
Magnetic energy and electrostatic potential energy are related by Maxwell's equations. The potential energy of a magnet or magnetic moment \mathbf in a magnetic field \mathbf is defined as the mechanical work of the magnetic force (actually magnet ...
in the Sun's atmosphere accelerates
charged particle
In physics, a charged particle is a particle with an electric charge. It may be an ion, such as a molecule or atom with a surplus or deficit of electrons relative to protons. It can also be an electron or a proton, or another elementary pa ...
s in the surrounding
plasma. This results in the emission of electromagnetic radiation across the
electromagnetic spectrum
The electromagnetic spectrum is the range of frequencies (the spectrum) of electromagnetic radiation and their respective wavelengths and photon energies.
The electromagnetic spectrum covers electromagnetic waves with frequencies ranging from ...
.
High-energy electromagnetic radiation from solar flares is absorbed by the
daylight side of Earth's upper atmosphere, in particular the
ionosphere
The ionosphere () is the ionized part of the upper atmosphere of Earth, from about to above sea level, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. It plays an ...
, and does not reach the surface. This absorption can temporarily increase the ionization of the ionosphere which may interfere with
short-wave radio
Shortwave radio is radio transmission using shortwave (SW) radio frequencies. There is no official definition of the band, but the range always includes all of the high frequency band (HF), which extends from 3 to 30 MHz (100 to 10 m ...
communication. The prediction of solar flares is an active area of research.
Flares also occur on other stars, where the term ''
stellar flare
The asterisk ( ), from Late Latin , from Ancient Greek , ''asteriskos'', "little star", is a typographical symbol. It is so called because it resembles a conventional image of a heraldic star.
Computer scientists and mathematicians often voc ...
'' applies.
Description
Solar flares affect all layers of the solar atmosphere (
photosphere
The photosphere is a star's outer shell from which light is radiated.
The term itself is derived from Ancient Greek roots, φῶς, φωτός/''phos, photos'' meaning "light" and σφαῖρα/''sphaira'' meaning "sphere", in reference to it ...
,
chromosphere, and
corona
Corona (from the Latin for 'crown') most commonly refers to:
* Stellar corona, the outer atmosphere of the Sun or another star
* Corona (beer), a Mexican beer
* Corona, informal term for the coronavirus SARS-CoV-2, which causes the COVID-19 di ...
). The
plasma medium is heated to tens of millions of
kelvin
The kelvin, symbol K, is the primary unit of temperature in the International System of Units (SI), used alongside its prefixed forms and the degree Celsius. It is named after the Belfast-born and University of Glasgow-based engineer and phy ...
s, while
electron
The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family,
and are generally thought to be elementary particles because they have no kn ...
s,
proton
A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron mass ...
s, and heavier
ion
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...
s are accelerated to near the
speed of light
The speed of light in vacuum, commonly denoted , is a universal physical constant that is important in many areas of physics. The speed of light is exactly equal to ). According to the special theory of relativity, is the upper limit ...
. Flares produce
electromagnetic radiation
In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic field, electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, inf ...
across the
electromagnetic spectrum
The electromagnetic spectrum is the range of frequencies (the spectrum) of electromagnetic radiation and their respective wavelengths and photon energies.
The electromagnetic spectrum covers electromagnetic waves with frequencies ranging from ...
at all
wavelength
In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats.
It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tro ...
s, from
radio waves
Radio waves are a type of electromagnetic radiation with the longest wavelengths in the electromagnetic spectrum, typically with frequencies of 300 gigahertz ( GHz) and below. At 300 GHz, the corresponding wavelength is 1 mm (s ...
to
gamma ray
A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically ...
s. Most of the energy is spread over frequencies outside the visual range; the majority of the flares are not visible to the naked eye and must be observed with special instruments. 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 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 10
20 joule
The joule ( , ; symbol: J) is the unit of energy in the International System of Units (SI). It is equal to the amount of work done when a force of 1 newton displaces a mass through a distance of 1 metre in the direction of the force applie ...
s of
energy
In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of heat a ...
suffices to produce a clearly observable event, while a major event can emit up to 10
25 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
The solar cycle, also known as the solar magnetic activity cycle, sunspot cycle, or Schwabe cycle, is a nearly periodic 11-year change in the Sun's activity measured in terms of variations in the number of observed sunspots on the Sun's surfa ...
. It can range from several per day during
solar maximum
Solar maximum is the regular period of greatest solar activity during the Sun's 11-year solar cycle. During solar maximum, large numbers of sunspots appear, and the solar irradiance output grows by about 0.07%. On average, the solar cycle tak ...
to less than one every week during
solar minimum
Solar minimum is the regular period of least solar activity in the Sun's 11-year solar cycle. During solar minimum, sunspot and solar flare activity diminishes, and often does not occur for days at a time. On average, the solar cycle takes abou ...
. 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
Erich Otto Ernst Rieger (born 1935 in Würzburg, Germany) is a German astrophysicist who spent his research career at the Max Planck Institute for Extraterrestrial Physics (MPE) near Munich
Munich ( ; german: München ; bar, Minga ) i ...
discovered with coworkers in 1984 an approximately 154 day period in the occurrence of
gamma-ray
A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically sh ...
emitting solar flares at least since the
solar cycle 19
Solar may refer to:
Astronomy
* Of or relating to the Sun
** Solar telescope, a special purpose telescope used to observe the Sun
** A device that utilizes solar energy (e.g. " solar panels")
** Solar calendar, a calendar whose dates indica ...
. The period has since been confirmed in most heliophysics data and the
interplanetary magnetic field
The interplanetary magnetic field (IMF), now more commonly referred to as the heliospheric magnetic field (HMF), is the component of the solar magnetic field that is dragged out from the solar corona by the solar wind flow to fill the Solar Sy ...
and is commonly known as the
''Rieger period''. The period's
resonance
Resonance describes the phenomenon of increased amplitude that occurs when the frequency of an applied periodic force (or a Fourier component of it) is equal or close to a natural frequency of the system on which it acts. When an oscillatin ...
harmonics
A harmonic is a wave with a frequency that is a positive integer multiple of the '' fundamental frequency'', the frequency of the original periodic signal, such as a sinusoidal wave. The original signal is also called the ''1st harmonic'', ...
also have been reported from most data types in the
heliosphere
The heliosphere is the magnetosphere, astrosphere and outermost atmospheric layer of the Sun. It takes the shape of a vast, bubble-like region of space. In plasma physics terms, it is the cavity formed by the Sun in the surrounding interstell ...
.
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
In a distribution, full width at half maximum (FWHM) is the difference between the two values of the independent variable at which the dependent variable is equal to half of its maximum value. In other words, it is the width of a spectrum curve mea ...
(FWHM) time of
soft X-ray
An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30 ...
flux within the wavelength bands measured by the
GOES
Goes () is a city and municipality in the southwestern Netherlands on Zuid-Beveland, in the province of Zeeland. The city of Goes has approximately 27,000 residents.
History
Goes was founded in the 10th century on the edge of a creek: de Kort ...
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.
Solar flares lasting longer than approximately 30 minutes are regarded as long duration events (LDE).
Post-eruption loops and arcades
![Coronal arcade](https://upload.wikimedia.org/wikipedia/commons/b/b3/Coronal_arcade.png)
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
Magnetic reconnection is a physical process occurring in highly conducting plasmas in which the magnetic topology is rearranged and magnetic energy is converted to kinetic energy, thermal energy, and particle acceleration. Magnetic reconnecti ...
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.
[The Mysterious Origins of Solar Flares]
, ''Scientific American'', April 2006 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's 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 (10
9 electron volt
In physics, an electronvolt (symbol eV, also written electron-volt and electron volt) is the measure of an amount of kinetic energy gained by a single electron accelerating from rest through an electric potential difference of one volt in vacuum ...
) 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 classification
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/m
2) of
soft X-ray
An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30 ...
s with
wavelength
In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats.
It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tro ...
s , as measured by the
GOES
Goes () is a city and municipality in the southwestern Netherlands on Zuid-Beveland, in the province of Zeeland. The city of Goes has approximately 27,000 residents.
History
Goes was founded in the 10th century on the edge of a creek: de Kort ...
spacecraft in
geosynchronous orbit.
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/m
2 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
A backronym is an acronym formed from an already existing word by expanding its letters into the words of a phrase. Backronyms may be invented with either serious or humorous intent, or they may be a type of false etymology or folk etymology. The ...
''moderate'' for M-class flares and ''extreme'' for X-class flares began to be used.
H-alpha classification
An earlier flare classification was based on
H-alpha
H-alpha (Hα) is a specific deep-red visible spectral line
A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared wit ...
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 × 10
12 km
2.)
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''.
Effects
Terrestrial
X-rays and extreme ultraviolet radiation emitted by solar flares are absorbed by the
daylight side of
Earth's atmosphere
The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing for ...
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
Ionization, or Ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecul ...
of the upper atmosphere, which can interfere with
short-wave radio
Shortwave radio is radio transmission using shortwave (SW) radio frequencies. There is no official definition of the band, but the range always includes all of the high frequency band (HF), which extends from 3 to 30 MHz (100 to 10 m ...
communication, and can temporarily heat and expand the Earth's outer atmosphere. This expansion can increase drag on satellites in
low Earth orbit
A low Earth orbit (LEO) is an orbit around Earth with a period of 128 minutes or less (making at least 11.25 orbits per day) and an eccentricity less than 0.25. Most of the artificial objects in outer space are in LEO, with an altitude never mor ...
, which can lead to
orbital decay
Orbital decay is a gradual decrease of the distance between two orbiting bodies at their closest approach (the periapsis) over many orbital periods. These orbiting bodies can be a planet and its satellite, a star and any object orbiting it, or ...
over time.
Radio blackouts
The temporary increase in ionization of the daylight side of Earth's atmosphere, in particular the D layer of the
ionosphere
The ionosphere () is the ionized part of the upper atmosphere of Earth, from about to above sea level, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. It plays an ...
, 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
The National Oceanic and Atmospheric Administration (abbreviated as NOAA ) is an United States scientific and regulatory agency within the United States Department of Commerce that forecasts weather, monitors oceanic and atmospheric conditio ...
classifies radio blackouts by the peak soft X-ray intensity of the associated flare.
Magnetic crochet
The increased ionization of the D and E layers of the ionosphere caused by large solar flares increases the
electrical conductivity
Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current. A low resistivity indicates a material that readily allow ...
of these layers allowing for the flow of
electric current
An electric current is a stream of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is measured as the net rate of flow of electric charge through a surface or into a control volume. The moving pa ...
s. 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
A crochet hook (or crochet needle) is an implement used to make loops in thread or yarn and to interlock them into crochet stitches. It is a round shaft pointed on one end, with a lateral groove behind it. The point eases the insertion of the hook ...
. These disturbances are relatively minor compared to those induced by geomagnetic storms.
In space
For astronauts in space, an expected radiation dose from the electromagnetic radiation emitted during a solar flare is about 0.05
gray
Grey (more common in British English) or gray (more common in American English) is an intermediate color between black and white. It is a neutral or achromatic color, meaning literally that it is "without color", because it can be composed o ...
, which is not immediately lethal on its own. Of much more concern for astronauts is the
particle radiation
Particle radiation is the radiation of energy by means of fast-moving subatomic particles. Particle radiation is referred to as a particle beam if the particles are all moving in the same direction, similar to a light beam.
Due to the wave–par ...
associated with solar particle events.
Observations
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 line
A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to iden ...
s. They normally produce
bremsstrahlung
''Bremsstrahlung'' (), from "to brake" and "radiation"; i.e., "braking radiation" or "deceleration radiation", is electromagnetic radiation produced by the deceleration of a charged particle when deflected by another charged particle, typicall ...
in X-rays and
synchrotron radiation in radio.
History
Optical observations
![Carrington Richard sunspots 1859](https://upload.wikimedia.org/wikipedia/commons/e/e5/Carrington_Richard_sunspots_1859.jpg)
Solar flares were first observed by
Richard Carrington
Richard Christopher Carrington (26 May 1826 – 27 November 1875) was an English amateur astronomy, amateur astronomer whose 1859 astronomical observations demonstrated the existence of solar flares as well as suggesting their electrical influ ...
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
The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called ''visible light'' or simply light. A typical human eye will respond to wavel ...
.
[Description of a Singular Appearance seen in the Sun on September 1, 1859]
, ''Monthly Notices of the Royal Astronomical Society
''Monthly Notices of the Royal Astronomical Society'' (MNRAS) is a peer-reviewed scientific journal covering research in astronomy and astrophysics. It has been in continuous existence since 1827 and publishes letters and papers reporting orig ...
'', v20, pp13+, 1859
Since flares produce copious amounts of radiation at
H-alpha
H-alpha (Hα) is a specific deep-red visible spectral line
A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared wit ...
, 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
During
World War II
World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
, 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
Grote Reber (December 22, 1911 – December 20, 2002) was an American pioneer of radio astronomy, which combined his interests in amateur radio and amateur astronomy. He was instrumental in investigating and extending Karl Jansky's pioneering wo ...
was the first to report radioastronomical observations of the Sun at 160 MHz. The fast development of
radioastronomy
Radio astronomy is a subfield of astronomy that studies celestial objects at radio frequencies. The first detection of radio waves from an astronomical object was in 1933, when Karl Jansky at Bell Telephone Laboratories reported radiation coming f ...
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
![ExtremeEvent 20120304-00h 20120317-24h](https://upload.wikimedia.org/wikipedia/commons/5/5a/ExtremeEvent_20120304-00h_20120317-24h.jpg)
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
MAG4was 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
A solar flare has been the main plot device for science fiction stories:
*
''Flare'', a 1992 novel by
Roger Zelazny
Roger Joseph Zelazny (May 13, 1937 – June 14, 1995) was an American poet and writer of fantasy and science fiction short stories and novels, best known for ''The Chronicles of Amber''. He won the Nebula Award three times (out of 14 nomin ...
and
Thomas Thurston Thomas
Thomas Thurston Thomas (born 1948), also writing as Thomas T. Thomas and Thomas Wren, is primarily a science fiction author.
Thomas was born in Summit, New Jersey, in 1948. He attended Warren Area High School and graduated in 1966. He then atte ...
*
''Inconstant Moon'', a 1996 ''Outer Limits'' episode on
Showtime
Showtime or Show Time may refer to:
Film
* ''Showtime'' (film), a 2002 American action/comedy film
* ''Showtime'' (video), a 1995 live concert video by Blur
Television Networks and channels
* Showtime Networks, a division of Paramount Global w ...
by writer
Larry Niven
Laurence van Cott Niven (; born April 30, 1938) is an American science fiction writer. His best-known works are ''Ringworld'' (1970), which received Hugo, Locus, Ditmar, and Nebula awards, and, with Jerry Pournelle, ''The Mote in God's Eye'' ...
and starring
Michael Gross and
Joanna Gleason
Joanna Gleason (née Hall; born June 2, 1950) is a Canadian actress and singer. She is a Tony Award–winning musical theatre actress and has also had a number of notable film and TV roles. She's known for originating the role of the Baker's Wife ...
*
Tamizhuku En Ondrai Azhuthavum
''Tamizhuku En Ondrai Azhuthavum'' (; also referred to as ''TEOA'') is a 2015 Indian Tamil-language thriller film written and directed by Ramprakash Rayappa. Produced by V. Chandran, the film stars Nakul, Attakathi Dinesh, Bindu Madhavi and Ais ...
, a 2015 tamil language film directed by
Ramprakash Rayappa and starring
Nakul
In the Hindu epic Mahabharata, ''Nakula'' (Sanskrit: नकुल) was fourth of the five Pandava brothers. Nakula and Sahadeva were twins blessed to Madri, by Ashwini Kumaras, the divine physicians. Their parents Pandu and Madri - died early ...
* Every Little Thing, the season two premiere of the a 2019
AppleTV+ series
''For All Mankind'' created by
Ronald D. Moore, Matt Wolpert and Ben Nedivi
*
''Finch'', a 2021
AppleTV+ film directed by
Miguel Sapochnik
Miguel Sapochnik (born 1 July 1974) is an English film and television director of Argentine origin, and former storyboard artist. For his work as a director on the HBO epic fantasy series ''Game of Thrones'', he won the award for Outstanding ...
and starring
Tom Hanks
Thomas Jeffrey Hanks (born July 9, 1956) is an American actor and filmmaker. Known for both his comedic and dramatic roles, he is one of the most popular and recognizable film stars worldwide, and is regarded as an American cultural icon. Ha ...
*
''Stowaway'', a 2021
science-fiction
Science fiction (sometimes shortened to Sci-Fi or SF) is a genre of speculative fiction which typically deals with imaginative and futuristic concepts such as advanced science and technology, space exploration, time travel, parallel univers ...
thriller film
Thriller film, also known as suspense film or suspense thriller, is a broad film genre that evokes excitement and suspense in the audience. The suspense element found in most films' plots is particularly exploited by the filmmaker in this genre ...
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
Robert Carlyle (born 14 April 1961) is a Scottish actor. His film work includes '' Trainspotting'' (1996), ''The Full Monty'' (1997), ''The World Is Not Enough'' (1999), ''Angela's Ashes'' (1999), '' The Beach'' (2000), ''28 Weeks Later'' (20 ...
and
Victoria Hamilton
Victoria Hamilton (born 5 April 1971) is an English actress.
After training at the London Academy of Music and Dramatic Art, Hamilton began her career in classical theatre, appearing in productions with the Royal Shakespeare Company and the ...
They are also a popular
doomsday scenario in disaster films, where their effects on Earth are often greatly exaggerated.
See also
References
External links
*
NOAA
The National Oceanic and Atmospheric Administration (abbreviated as NOAA ) is an United States scientific and regulatory agency within the United States Department of Commerce that forecasts weather, monitors oceanic and atmospheric conditio ...
Space Weather Prediction Center
The Space Weather Prediction Center (SWPC), named the Space Environment Center (SEC) until 2007, is a laboratory and service center of the US National Weather Service (NWS), part of the National Oceanic and Atmospheric Administration (NOAA), loc ...
's near real-time solar flare data and resources:
*
GOES X-Ray Flux (1-minute data)*
GOES Solar Ultraviolet Imager (SUVI)*
D Region Absorption Predictions (D-RAP)*
3-Day Forecast*
Forecast Discussion*
{{Authority control
Flare
A flare, also sometimes called a fusée, fusee, or bengala in some Latin-speaking countries, is a type of pyrotechnic that produces a bright light or intense heat without an explosion. Flares are used for distress signaling, illumination, ...
Space plasmas
Plasma physics
Articles containing video clips
Cosmic doomsday