Solar flare is an important manifestation of solar activity and one of the most intense activities on the sun[23]Is a sudden and large-scale energy release process in local areas of the solar surface, which causes local areas to be heated instantaneously and emit various kinds of energyelectromagnetic radiation, accompanied byParticle radiationSudden increase, and the wavelength of the emitted light spans the wholeElectromagnetic spectrum。[4]
Solar flares can be divided into five levels: A, B, C, M, X, where A is the minimum energy level and X is the maximum energy level.[28]
Because the background radiation of the solar photosphere is too strong, most flares cannot be observed in white light. The radiation enhancement is mainly on some spectral lines, among which the H α line of hydrogen (wavelength: 6563 angstrom, color: orange red) and the H and K lines of ionized calcium (wavelength: 3968 angstrom and 3934 angstrom, respectively) are the most prominent.When these monochromatic lights are used to monitor the solar chromosphere, sudden brightening of local small areas can sometimes be seen in the spectral spots near the active region.The brightening area rapidly brightens several times or even dozens of times from the original spectral brightness in a few minutes, and then slowly recovers to the original spectral brightness in a few minutes to 1~2 hours.In July 1892,U.S.Aastronomerhale The monochromatic images of solar flares were observed for the first time.Before the 1950s, solar flares mainly relied on the spectral observation of H α monochromatic light and visible region.The comprehensive observation by various means shows that when the flare occurs, the electromagnetic radiation of almost all bands increases from gamma rays and X-rays with a wavelength shorter than 1 A to radio bands with a wavelength up to several kilometers, and the emitted energy ranges from 10threeElectron volts up to 10nineVarious particle streams of electron volts.Among them, the enhancement of electromagnetic radiation mainly occurs in short wave radiation (X-ray and ultraviolet light) and radio band.Therefore, a more accurate definition of flare should include all the above series of abrupt phenomena, and the enhancement of H α radiation is only a secondary sign of flare occurrence.[1]
On May 14, 2024 local time, the sun erupted a strongest flare (X8.7).[28]
Chinese name
Solar flare
Foreign name
Solar flare
Abbreviation
solar flare
Occurrence site
Heliosphere
Cause
Sudden release of solar magnetic energy
Occurrence rule
Periodic change of about 11 years
Classification
Optical flare, X-ray flare, proton flare
Energy
Equivalent to tens of billions of giant hydrogen bombs exploding simultaneously
On the morning of September 1, 1859, British astronomy enthusiastsCarringtonAs usual, in our own astronomical observation roomSunspotConduct routine observation.What made him incredible happened. Two extremely bright white lights suddenly appeared near a large complex sunspot group on the north side of the sun. Their brightness increased rapidly, far exceeding the photosphere background. The bright white light only lasted for a few minutes and soon disappeared.On the same day, British astronomer Roy Hodgson also saw this sudden phenomenon on the sun.This is the first record of flares, and also the first record of white light flares.
Flare genesis
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Solar flare is an active phenomenon that the local area of the solar atmosphere suddenly brightens, and it is a large-scale explosion of solar electromagnetic radiation.It is the most intense explosive activity in the solar atmosphere, lasting from a few minutes to several hours.[6]
Observations of sunspots, magnetic fields and H α before flares
Solar atmosphereIs full of magnetic field. The more complex the magnetic field structure is, the easier it is to store more magnetic energy.When there is too much magnetic energy stored in the magnetic field, it will release energy through the solar eruption. Solar flares are a form of solar eruption.
Long term observations have found that most flares occur above the sunspot group, and the more complex the structure of the sunspot group and the polarity of the magnetic field, the higher the probability of large flares.On average, a normally developing sunspot group will produce a flare almost in a few hours, but there are few flares that have a strong impact on the Earth.
Flare classification
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Solar flare
According to different observation methods, it can be divided into optical flares, X-ray flares, etc.Generally, the flares observed by monochromatic light in the visible light range are customarily called optical flares, the flares observed in the X-ray band are called X-ray flares, and the flares corresponding to proton events are called proton flares.
Optical Flares
English name: Optical solid flare
Flare bursts observed by H α (BBSO, 1972-08-07)
When the sun burstsOptical band brightnessThe phenomenon of sudden enhancement is called optical flare;The wavelength is between 3900 and 7000 angstroms.The flare is most prominent on the H α line of hydrogen and the H, K lines of ionized calcium, which is very conducive to the observation of optical flares.
X-ray flare
English name: X-ray flare
The phenomenon that the X-ray flux suddenly increases when the sun bursts is called X-ray flare;The wavelength is between 0.01 and 100 angstroms.The flare has obvious performance in the extreme ultraviolet band and can be used for monitoring.
Proton flare
English name: Solar proton flare
In the particle events emitted by flares, when the proton energy detected by the geosynchronous orbit is more than 10 MEV and the flux exceeds 10 pfu, it indicates that there is a strong proton flow in this event, that is, a proton event occurs. The corresponding source flare is called a proton flare.Under the guidance of the interplanetary magnetic field in the solar terrestrial space, the protons emitted from the eastern hemisphere of the solar surface generally cannot reach near the Earth, so the proton flares mainly occur in the western hemisphere of the solar surface.Most of the proton flares are M level and above flares, and the proton events caused by them can be observed near the Earth orbit within 1 hour to 2 hours after their occurrence.
White flare
White light flare is one of the rare solar flares, which is named after its ability to be observed in the white light range.Solar flares cannot be observed by white light generally, but only by H α lines and H, K lines of ionized calcium.But sometimes in some smaller areas of the bright area seen by the H α line, sudden brightening can also be seen through white light, which lasts for about a few minutes. This is the white light flare.The first solar flare observed by Carrington in 1859 was a white light flare.
Flare energy
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The duration of the flare is from a few minutes to tens of minutes, but it can release 10twenty～10twenty-fiveThe huge energy of joules, which is equivalent to tens of billions of giantHydrogen bombThe energy released by the explosion at the same time, or equivalent to 100000 to a million times strongVolcano eruptionThe total energy released shows its great power.However, for the huge energy of the sun, it only accounts for about one tenth of the total solar radiation energy.
Flare intensity classification
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The size of the flare area is an important index of the flare radiation scale. Internationally, the area when the flare brightness reaches the maximum is used as the main basis for the flare level, and the maximum brightness of the flare is qualitatively described.According to the H α monochromatic light area of the flare, the optical flare can be divided into five levels, which are represented by S, 1, 2, 3 and 4 respectively.Adding F, N, B after the level indicates whether the maximum brightness of the optical flare in the H α line is weak, ordinary, or strong.So the largest and brightest flare is 4B, and the smallest and darkest is SF.
Classification standard of optical flares
Optical Flares
level
Flare area
(Unit: 10-6Solar Hemisphere Area)
S
one
100~250
two
250~600
three
600~1200
four
>1200
Earth's ionosphereIt is sensitive to the change of solar soft X-ray radiation intensity, so the soft X-ray radiation intensity of 1~8 A is also widely used internationally to grade X-ray flares.According to the magnitude of soft X-ray peak flow observed by the U.S. GOES satellite, the flare is divided into five levels, namely A, B, C, M and X, and the released energy increases in turn.The value after each grade represents the specific value of X-ray peak flow.For example, M2 indicates that the peak flow of flare soft X-ray is 2 × 10-2Watts per square meter.
Generally speaking, flares below level C are small flares;M-class flares are medium flares;Class X flares are large flares.
During the Halloween solar storm from the end of October to the beginning of November 2003 (named after the Western Halloween), a series of large flares broke out on the sun.Among them, the X28 flare on November 4 is the largest flare since GOES satellite observation.
Solar flares can be divided into five levels: A, B, C, M, X, where A is the minimum energy level and X is the maximum energy level.[23]
Classification criteria for X-ray flares
X-ray flare
level
Peak flow of X-ray
(Unit: W/m2)
A
-7
B
ten-7～10-6
C
ten-6～10-5
M
ten-5～10-4
X
>10-4
Flare occurrence rule
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The flare occurrence shows periodicity with the change of solar activity cycle
The occurrence frequency of flares varies withSolar cycleThe change of the solar cycle shows a periodicity of about 11 years, and the average length of a solar cycle is 11.2 years[23], the location of the outbreak shows the distribution of butterfly patterns over time.In the years of extreme solar activity, flares above M level occur every day on average;In the very low solar activity years, there is almost no flare of M level or above in the whole year.
In a solar activity cycle, there are about 10 flares of X10 level and above, about 200 flares of X level, and about 2000 flares of M level.
The 25th from January to October 2024Solar cycleThe activity peak is the "solar maximum period", and the sun is expected to reach the peak of the current activity cycle in 2024.[18]
History
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In September 1859Carrington17.5 hours after the first observation of solar flare eruption, strong geomagnetic disturbances were recorded by geomagnetic stations.The next day, many parts of the world (including ChinaHebeiThe beautiful aurora was observed.
On February 27 and 28, 1942, a radar station in Britain received strong noise interference. At that time, a big flare happened, and a big magnetic storm appeared one day later.
On September 23, 1956, some Asian observatories observed a large flare, which, in addition to the above-mentioned disturbance of the Earth's space environment, also greatly enhanced the intensity of cosmic rays on the ground. One hour after the flare was generated, an abnormal ionospheric absorption phenomenon occurred near the polar region of the Earth's back solar surface hemisphere.The observation of more flare eruptions has gradually made people realize that flares can produce significant disturbances to the Earth's environment and affect human life.
On September 3, 2017, an AR2673Sunspot groupIt has triggered more than 10 solar flares in 5 days, including the solar flare on September 4Coronal mass ejectionAnd directly led to the intermediate solar proton event.[2]
FY-3E clearly recorded the eruption in space[5]
On March 29, 2022, there were 17 consecutive flares.There were 11 C-level small flares and 6 M-level medium flares, accompanied by coronal mass ejections, which were unusual events in the past day.The explosion was clearly recorded by FY-3E in space.The eruptive activities were all concentrated on sunspot 12975.[5]
The X2.2 Large Flare on April 20, 2022[8]
At 12:03 p.m. on April 20, 2022, the National Space Science Center of the Chinese Academy of Sciences, the Space Environment Prediction Center.Like the No. 026 forecaster, the No. 029 and No. 037 forecasters are also staring at the solar X-ray flux and extreme ultraviolet imaging data.With years of professional training, they judged from the red and green curves and the bright spots on the western edge of the solar surface that the level of this flare was very large.The big flare appeared at 11:46 a.m., and it was not until 12:03 p.m. that the curve on the screen finally eased, and the bright spot also faded.[7]On April 20, the intensity level of the X flare reached X2.2.The big flare lasts for 17 minutes, which is a relatively normal time.Eight minutes later, the sharply increased electromagnetic radiation arrived in China, causing sudden disturbance of the ionosphere in China, interfering with the propagation of radio signals and causing the attenuation of short wave radio signals.[8]
At 16:25 on October 2, 2022 (4:25 on October 3, 2022, Beijing time), according to NASA, the agency's Solar Dynamics Observatory found a huge burst of solar radiation in its observation, and took pictures of the flare at that time. The intensity of the solar flare was X1[9]。
According to the news on the space weather WeChat official account on December 15, 2023: At 01:03 on the 15th Beijing time, a large flare with an intensity of X2.8 broke out in the solar activity area 13514.This flare activity was the strongest eruption since the X8.2 flare on September 10, 2017, which caused a strong radio signal absorption event and blocked the transmission of shortwave radio communication and navigation low-frequency signals for about an hour.[11]
At 05:55 on January 1, 2024, Beijing time, the sun erupted a strong flare (X5.0 level)。[12]The event occurred at dawn in China, and had little impact on the ionosphere over China.Moreover, the location of this eruption is not right for the earth, so it will not cause great earth space environmental effects.[13]
At 6:34 on February 23, Beijing time, the sun broke out the most intense flare of the 25th solar cycle so far: the X6.3 large flare, which also broke the intensity of flares since 2017Records.[14-15]
Solar monitoring image SDO satellite during flare eruption
At 4:56 on March 29, 2024, a flare activity broke out in the solar active region 13615, and the peak intensity reached X1.1.When the flare occurred, China was in the early morning, so there was no impact on the ionospheric environment over China.In the past 24 hours, in addition to this X1.1 flare activity, there have also been three strong eruptions of M7.1, M6.1, and M3.2 in the active region 13615, and it has not yet entered the back ground with the sun's rotation, so we cannot take it lightly.[16][29]
At 10:22 on May 3, 2024, the sun erupted a strong flare (level X1.6).When the flare occurred, China was in the daytime, and the flare had an impact on the ionosphere over China.[17-18]
The National Space Weather Monitoring and Early Warning Center released the solar flare information to remind that at 14:01 on May 5, 2024, Beijing time, the sun broke out a strong flare (X1.3 level).The event occurred in daytime in China, and the flare had an impact on the ionosphere over China.It is estimated that M level or even X level flares may still erupt in the next three days.[19]
On May 5, 2024, the National Space Weather Monitoring and Early Warning Center released the solar flare information to remind that at 14:01 Beijing time on May 5, 2024, the sun broke out a strong flare (level X1.3).At the time of the event, China was in the daytime, and the flare had an impact on the ionosphere over China.It is estimated that M level or even X level flares may still erupt in the next three days.[20]
At 14:35 on May 6, 2024, the active region 13663 located in the northwest of the sun erupted a large flare of level X4.5, which is the third strong flare activity of the sun in less than two days after the X1.3 and X1.2 levels on May 5.[21]The National Space Weather Monitoring and Early Warning Center predicted that M-level or even X-level flares might still erupt from the 6th to the 8th.[22]
At 14:00 on May 8, 2024, the National Space Weather Monitoring and Warning Center issued a yellow flare warning: at 9:41 and 13:08 on May 8, 2024, Beijing time, the flow of solar soft X-ray reached the level of strong flares twice (X1.0).[24]
From May 3 to May 8, 2024, the sun will continue to have strong eruptions, mainly in the form of flares. Among them, there will be 6 large flares with intensity up to X, and 24 moderate flares with intensity up to M, which is the most frequent continuous occurrence of X flares in the sun during the current 25th solar activity cycle and in the past 20 years.[25]
On May 10, 2024, the National Space Weather Monitoring and Early Warning Center released the solar flare information to remind that at 01:44 Beijing time on May 10, 2024, the sun broke out a strong flare (X1.1 level).The event occurred at night in China, and the flare did not affect the ionosphere above China.[26]
From May 3 to May 11, 2024, in just 9 days, 11 X-level flares and more than 60 M-level flares have erupted on the sun, and the intensity and frequency of the eruptions are rare in history.[27]
On May 14, 2024 local time, according to the Associated Press,National Oceanic and Atmospheric AdministrationHe said that the National Aeronautics and Space Administration (NASA) Solar Dynamics Observatory observed that the sun had erupted the strongest flare since 2005, with the intensity ofTo X8.7.[28]
At 00:51 on May 15, 2024, Beijing time, the solar active region 13664 erupted flare activity, and the peak intensity of the flare was X8.7, reaching the level of large flare.So far, the active region 13664 has erupted 10 times of Class X flares in the past week, and this eruption also broke the record of the strongest flare in the current 25th solar cycle.[29]
On June 2, 2024, the National Space Weather Monitoring and Early Warning Center of the China Meteorological Administration issued an information reminder that at 3:39 on June 2, Beijing time, the solar active region 13697 erupted a medium flare with an intensity of M7.3, accompanied by obvious coronal mass ejection activity, and the eruption type was a halo eruption.Affected by this, it is expected that small to medium geomagnetic storms may occur around June 4.[30]
Areas of influence
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Space flight impact
Enhanced ultraviolet and X-ray radiationthe ionosphereThe sharp increase of the electron concentration in can cause sudden ionospheric disturbance, which can lead to the fading or even interruption of short wave radio signals.After the enhanced ultraviolet radiation is directly absorbed by the earth's atmosphere, it heats the atmosphere, and the temperature and density of the atmosphere rise, thus making man-made satellites, etcSpacecraftThe orbit of the is changed;The enhancement of ultraviolet radiation also makes the density of atomic oxygen suddenly increase, thus accelerating the denudation of atomic oxygen on the surface of spacecraft.
Impact on communication
Short wave communication is mainly carried out by reflection of layer F.However, when sudden ionospheric disturbance occurs, due to the sudden increase of electron density near layer D, the radio waves that pass through layer D and shoot to layer E and layer F and reflect back to the ground are strongly absorbed, causing the attenuation of radio waves.The higher the electron density of D layer is, the stronger the absorption is.If the electronic density of layer D is so large that the highest available frequency of shortwave communication is also seriously absorbed, then communication will be interrupted.
Broadcast signal influence
In real life, when we listenradio broadcastThe signal will suddenly become cluttered and cannot be heard. Sometimes when we adjust the frequency, the signal will be clearer, but sometimes it still cannot be heard clearly. This situation will generally recover by itself soon.This may be the effect of distant solar flares on radio signals.
Impact on navigation
VLF navigation or communication signals are mainly transmitted between a waveguide between the ground and the bottom of the ionosphere. Radio waves are reflected and propagated back and forth between the earth and the ionosphere, which can achieve long-distance transmission.When sudden disturbance occurs in the ionosphere, the bottom of the ionosphere changes due to the decrease of the reflection height of layer D, resulting in the change of the propagation phase delay of low-frequency or very low-frequency signals between a given transmitter and receiver, which can cause navigation errors of tens of kilometers in serious cases.
When the solar flare bursts, it will cause the disturbance of the earth's ionosphere on the sunny side, thus affecting navigation and positioning systems, aviation communications, short wave communications and other emergency communications.[23]
Impact on satellites
Solar flares and solar eruptions will affect radio communications, power grids, navigation signals, and pose a threat to spacecraft and astronauts.Explosive flares are usually accompanied by coronal mass ejections, and the geomagnetic storms caused by coronal mass ejections will affect many fields, including aviation, aerospace, navigation, communication, pipe networks and so on.In February 2022, a batch of 49 "star chain" satellites deployed by SpaceX suffered heavy losses due to geomagnetic storms, and as many as 40 satellites were scrapped.[6]
Solar flares may also be accompanied by solar proton events and coronal mass ejections. A large number of high-energy particles arrive near the Earth, which may damage satellites in Earth orbit and threaten the life safety of astronauts;When the coronal mass ejection reaches near the earth, it will cause geomagnetic disturbance or even geomagnetic storm, affect long-distance power transmission network and oil pipeline, and also affect satellite launch activities, especially for low orbit satellites.[23]
Impact on human body
Although the solar flare eruption will carry a large amount of electromagnetic radiation and high-energy particles, in fact only a small part can reach near the earth. In addition, the earth has its own magnetic field protection, so even a strong flare eruption has almost no impact on human health, and the public need not worry about it, nor do they need to do special protection.[23]
Flare forecast
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Data and analysis of flare prediction basis
Flare forecast is a short-term forecast of the occurrence probability and intensity of flares in 1~3 days according to the three levels of C and below, M and X.The physical prediction model of solar flares has not yet been established, and most of them rely on the monitoring of sunspot centered active areas and the statistics of historical relevant data.[3]
In the face of space weather events caused by strong solar activities, the National Space Weather Monitoring and Warning Center established by the China Meteorological Administration has basically built a trinity business system of monitoring, forecasting and services, and basically has the monitoring capability for key nodes and key elements in the cause and effect chain of space weather,It can systematically and accurately forecast and warn important space weather processes such as geomagnetic storms.In the field of civil aviation, as the fourth global space weather center approved by the International Civil Aviation Organization, the National Space Weather Monitoring and Early Warning Center and the other three global centers take turns on duty, providing refined space weather forecast consulting services 24 hours a day, to protect the safety of global aviation.[23]
Observation instrument
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Hard X-ray imager for detecting non thermal radiation of solar flares;The Lehmann Alpha Solar Telescope can automatically monitor solar flare burstshair[10]。
Alert Level
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The warning level of flares is usually determined byGeosynchronous orbit satelliteThe observed solar X-ray flow is characterized by the radiation energy of 0.1nm~0.8nm solar X-ray received per unit time and per unit area, and the unit is W/mtwo。The solar X-ray flux of different orders of magnitude represents the X-ray flares of different orders, and the ray flux is greater than 10-3W/mtwoIt is a strong flare and gives a red alarm;Ray flow greater than 10-4W/mtwoIt is a medium flare and gives an orange alarm;Ray flow greater than 10-5W/mtwoIt is a weak flare, and a yellow alarm is issued.Solar X-ray flares cause the increase of ionospheric electron density on the sunward side of the earth, affecting short wave radio communication and low-frequency navigation systems.The higher the level of flare, the more serious the impact on shortwave communication and low-frequency navigation system.
Alert Level
Index range
Possible impacts and hazards
Red alarm
Radiation flow ≥ 10-3
Communication: the shortwave radio communication in most areas facing the sun is interrupted for 1-2 hours, and the signal disappears;The low-frequency navigation signal is interrupted for 1-2 hours, causing small interference to the sunny side satellite navigation.
Orange Alert
ten-3>Radiation flow ≥ 10-4
Communication: shortwave radio communication is affected in a large area, and the sunny side signal is lost for about 1 hour, and the low-frequency radio navigation signal strength is attenuated for about 1 hour.
Yellow alarm
ten-4>Radiation flow ≥ 10-5
Communication: the strength of the short wave signal on the sunny side decreases slightly, and the strength of the low-frequency navigation signal decreases for a short time.
