Solar cosmic ray

Visible and invisible rays of light, magnetism, etc. produced by the movement of solar energetic particles

synonym Solar energetic particle (Solar high-energy particles) generally refer to solar cosmic rays

This entry is made by Compilation and application of scientific encyclopedia entries of "Science Popularization China" to examine.

High energy generated by solar activity Particle Flow , also known as sunlight High energy particles. The solar activity is mainly flare activity. The main components of solar cosmic rays are proton And electrons, including a small amount of other nuclear components. Recent observations have confirmed that some flares also radiate neutrons. The solar cosmic rays are not isolated. They are the visible and invisible rays of light, magnetism, etc., generated by the internal particle movement stimulated by the gravitational effect of galaxies.

Chinese name: Solar cosmic ray
Foreign name: solar cosmic rays
Alias: Solar energetic particle

Main components: Protons, electrons, a small amount of other nuclear components
Nature: radial
Classification: Electrification Particle Flow

catalog

seven directional

Proton flare

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When the solar activity is intense, there are many sub regions with strong magnetic gradient in the active region with complex magnetic field structure, and proton flares may occur. The characteristics are: there are solar radio bursts in centimeter and millimeter wave bands, and there are type II and type IV bursts; There are hard X-ray bursts, and the energy spectrum becomes hard. Solar particles may be accelerated from these regions to a relatively high energy, enter the heliospheric space, and form solar high-energy particle events. The flux of particles is closely related to the microwave radio characteristics.^[1]

Solar proton

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The energy in solar cosmic rays is higher than 5 × 10 eight The proton of electron volts can enter the earth's atmosphere and produce secondary particles. This high-energy event is called the relativistic solar cosmic ray event or the ground plane event. The number of ground level events is very small. From 1942 to 1978, only 31 events were recorded in the world. The largest one occurred on February 23, 1956, and the maximum magnetic stiffness of particles (see cosmic ray geomagnetic effect) was at least 2 × 10 ten Volts, magnetic stiffness over 10 nine The proton integral direction flux of V is 10 seven Particle/(m two ·Sphericity · s), equivalent to Galactic cosmic ray Tens of times the strength. This kind of high energy event Spacecraft It has certain damage effect with astronauts.

The energy in solar high-energy particles is less than 5 × 10 eight The solar protons with electron volts are called low-energy solar cosmic rays. Where the energy is higher than 10 × 10 six The protons of electron volts can enter the ionosphere in the polar region of the earth, increasing the electron density of layer D, leading to the attenuation of radio waves, forming a "polar cap absorption event", and even affecting the photochemical reaction of the upper atmosphere, increasing the atmospheric NO content, and reducing the ozone Composition. The polar cover absorbs events much more often than the ground level events. Of the 86 events recorded from 1956 to 1978 (including more than 10 ground level events), the largest one occurred on August 4, 1972. The radio wave absorption reached more than 60 decibels, and ozone decreased by about 20%. Events with lower energy can only be observed by satellite instruments, called“ Satellite sensitive events ”, it has more times. The lowest recorded energy of solar protons is about 3 × 10 five Electronic volts.

Energy spectral ratio of solar protons Galactic cosmic ray The energy spectrum is steep, or rather soft, which means that there are abundant low-energy particles High-energy particle Rare. The energy spectrum of different events is quite different, and the low-energy part is easy to change due to interplanetary propagation effect. The high energy spectrum is steep, and the power index is between 3.0 and 4.5; The low energy spectrum is relatively flat, and the power index is between 1.1 and 4.3. The high and low energy spectra of several events can be expressed by the kinetic energy power law spectrum with an index close to 3. Some events are expressed by the magnetic stiffness spectrum, and the low energy part is still relatively flat.^[1]

Nuclear composition and isotope

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Table is listed in Interplanetary space The measured nuclear composition of solar particles and their elements abundance 。 Under normal circumstances, the nuclear composition of low-energy events is quite close to that of the sun. At higher energies, its composition is also roughly similar to that of the sun. However, the nuclear composition of low-energy events changes greatly, especially the "iron rich event" that is, the abundance of heavy elements increases with the increase of nuclear charge (relative to the solar abundance). In recent years, observations have confirmed that the 3He isotope of this iron rich event is also quite abundant. Under normal circumstances, the 3He/4He value in the flare event is the estimated value of the photosphere (about 10 -4 ）It is generally believed that this is the product of the nuclear reaction between the flare particles and the solar atmosphere. But in the event of rich heavy elements, the value of 3He/4He unexpectedly exceeds 1, and Proton number It is greatly reduced, and 2H and 3H isotopes are not observed solar flare It is also often a small flare. One view is that this is due to the resonance heating caused by the interaction between the solar ion acoustic wave and the ions of 3He and other heavy nuclei.^[1]

Solar electron

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Solar electron due to Magnetic stiffness Low, can only be observed on satellites. Almost all solar proton events record solar electrons at the same time. Such events are called solar electron proton events. There are also pure electronic events without protons, with an energy of 2 × 10 four ～3×10 five Electronic volts. Flare characteristics of pure electronic events, except hard X-ray and microwave In addition to radio bursts, there are obvious differences with electron proton events. The radio burst is not type II or type IV, but type III. There is no correlation between electron flux and radio flux. The directional flux of a typical electronic event is 10 two Particle/(cm two ·Sphericity · s), up to 104 particles/(cm two ·Sphericity · second). However, the directional flux of pure electronic events is relatively small, only 10-10 two Particle/(cm two ·Sphericity · second). In the energy range of 12~45 MEV, the electron to proton flux ratio is 10 -2 ～5×10 -6 , average 10 -4 。 The energy spectrum indices of different electronic events have little difference, and the average value of differential energy spectrum indices γ=3.0 ± 0.4, while the γ value of proton events changes significantly.^[1]

accelerate

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In the sun Electronics - Proton event Non relativistic electrons often arrive at the earth before relativistic electrons and protons, which indicates that Low-energy electron Accelerated first. It is generally believed that the acceleration of solar particles includes two stages. First, the electrons are pre accelerated to non relativistic energy, and various types of pulse bursts are excited to form flares. Due to the action of electric field and wave, electrons further accelerate and converge into coronal electron streams, producing type III radio bursts, and the electron streams leave the sun and enter the interplanetary space; The second stage is when the flare burst reaches its maximum, a coronal shock wave is formed, and a type II radio burst is generated. Shock wave or other turbulence accelerates electrons to relativistic energy, and also accelerates protons to enter interplanetary space. High energy electrons excite synchrotron accelerating radiation in the magnetic field, forming type IV radio bursts.^[2]

Propagation effect

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When the solar cosmic ray enters the interplanetary space, it is affected by the solar wind and the interplanetary magnetic field, and the intensity and direction will change, which is called the propagation effect. After the occurrence of solar flares, it takes more than ten minutes or even tens of minutes to observe particles of various energies near the Earth. The arrival time of particles is longer than that converted according to their speed. Even particles with the same energy do not arrive at the same time. The intensity change of solar cosmic ray particles observed in interplanetary space has a time development process. The length of this process depends on the level of particle energy, but it is far more than the duration of flare activity itself. The particle strength first rapidly increases to a certain maximum value in a few minutes to several hours, and then approximately decays to the level before the increase in the form of exponential function over time, going through several hours to several days. According to the time change curve, it can be estimated that the propagation distance of particles is about 3-12 astronomical units, depending on the energy of particles. These time variation characteristics show that the solar cosmic ray has gone through a tortuous journey to reach the Earth, and it has neither walked in a straight line nor simply circumnavigated the interplanetary spiral magnetic line of force to reach the Earth. Its transport process is very similar to the diffusion process of a pulse point source. Interplanetary medium Very thin, only magnetic field Talent influence Solar particle The movement of. In interplanetary space, in addition to the large-scale magnetic field in the form of spiral lines (see Interplanetary magnetic field ）And the random small scale irregular magnetic field caused by the fluctuation and turbulence of the solar wind. It is this irregular magnetic field that makes the motion track of solar cosmic ray particles scatter randomly, forming diffusion motion.^[2]

directional

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Low energy solar cosmic rays have obvious directionality, that is, anisotropy. At the beginning of the event, the anisotropy is very large, up to 20~25%, and the direction is obviously along the direction of the interplanetary spiral west of the heliocentric line, which indicates that the particles first arrived at the observation point along the spiral magnetic line of force. As the particle strength increases to the maximum value, the particle density distribution near the earth tends to be uniform, so along the helical line The anisotropy of is also reduced. It is worth noting that the anisotropy gradually turns to the direction of the solar terrestrial line, that is, the solar wind. This means that except along the Magnetic line of force Besides the diffusion, there is also the transport process of convection with the solar wind. This convection effect is caused by the interplanetary magnetic field driven by the solar wind, which also drives the movement of cosmic ray particles, and plays a leading role in the later stage of the cosmic ray event. The solar wind convection will drive the density peak away from the sun. When the density peak passes through the observation point, the diffusion will turn to point to the sun along the direction of the magnetic field line. The combination of this reverse diffusion and the radial solar wind convection vector makes the anisotropic vector turn to the direction about 45 ° east of the solar terrestrial line. The time variation of the anisotropy of particles strongly indicates that the particles not only diffuse along the magnetic line of force, but also exist Radial convection effect 。 At the beginning of the event, diffusion played a leading role, while convection played a leading role in the later period.^[2]

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