concept sunny wind was introduced into astronomy at the end of the 40s of the 20th century, when the American astronomer S. Forbush, measuring the intensity of cosmic rays, noticed that it decreases significantly with increasing solar activity and drops quite sharply during .

It seemed rather strange. Rather, the opposite could be expected. After all, the Sun itself is a supplier of cosmic rays. Therefore, it would seem that the higher the activity of our daylight, the more particles it should throw into the surrounding space.

It remained to assume that the increase in solar activity affects in such a way that it begins to deflect particles of cosmic rays - to reject them.

It was then that the assumption arose that the culprits of the mysterious effect are streams of charged particles escaping from the surface of the Sun and penetrating the space of the solar system. This peculiar solar wind cleans the interplanetary medium, "sweeping out" particles of cosmic rays from it.

In favor of such a hypothesis, phenomena observed in . As you know, comet tails always point away from the Sun. Initially, this circumstance was associated with the light pressure of the sun's rays. However, it was found that light pressure alone cannot cause all the phenomena that occur in comets. Calculations have shown that for the formation and observed deflection of cometary tails, it is necessary to influence not only photons, but also particles of matter.

As a matter of fact, the fact that the Sun throws out streams of charged particles - corpuscles, was known even before that. However, it was assumed that such flows are episodic. But comet tails are always directed away from the Sun, and not only during periods of amplification. This means that the corpuscular radiation that fills the space of the solar system must also exist constantly. It intensifies with increasing solar activity, but it always exists.

Thus, the solar wind continuously blows around the solar space. What does this solar wind consist of, and under what conditions does it arise?

The outermost layer of the solar atmosphere is the corona. This part of the atmosphere of our daylight is unusually rarefied. But the so-called "kinetic temperature" of the corona, determined by the velocity of particles, is very high. It reaches a million degrees. Therefore, the coronal gas is completely ionized and is a mixture of protons, ions of various elements and free electrons.

Recently there was a message that the solar wind contains helium ions. This circumstance sheds light on the mechanism by which charged particles are ejected from the surface of the Sun. If the solar wind consisted only of electrons and protons, then one could still assume that it is formed due to purely thermal processes and is something like steam that forms above the surface of boiling water. However, the nuclei of helium atoms are four times heavier than protons and are therefore unlikely to be ejected by evaporation. Most likely, the formation of the solar wind is associated with the action of magnetic forces. Flying away from the Sun, plasma clouds, as it were, carry away magnetic fields with them. It is these fields that serve as that kind of "cement" that "fastens" together particles with different masses and charges.

Observations and calculations carried out by astronomers have shown that as we move away from the Sun, the density of the corona gradually decreases. But it turns out that in the region of the Earth's orbit it is still noticeably different from zero. In other words, our planet is inside the solar atmosphere.

If the corona is more or less stable near the Sun, then as the distance increases, it tends to expand into space. And the farther from the Sun, the higher the rate of this expansion. According to the calculations of the American astronomer E. Parker, already at a distance of 10 million km, coronal particles move at speeds exceeding the speed .

Thus, the conclusion suggests itself that the solar corona is the solar wind blowing around the space of our planetary system.

These theoretical conclusions have been fully confirmed by measurements on space rockets and artificial earth satellites. It turned out that the solar wind always exists near the Earth - it "blows" at a speed of about 400 km/sec.

How far does the solar wind blow? With theoretical considerations, in one case it turns out that the solar wind subsides already in the region of the orbit, in the other, that it still exists at a very large distance beyond the orbit of the last planet Pluto. But these are only theoretically the extreme limits of the possible propagation of the solar wind. Only observations can indicate the exact boundary.

There is a constant stream of particles ejected from the sun's upper atmosphere. We see evidence of the solar wind around us. Powerful geos magnetic storms can damage satellites and electrical systems on Earth, and cause beautiful auroras. Perhaps the best evidence of it is the long tails of comets as they pass near the sun.

Comet dust particles are deflected by the wind and carried away from the Sun, which is why comet tails always point away from our sun.

Solar wind: origin, characteristics

It comes from the upper layers of the Sun's atmosphere, called the corona. In this region, the temperature is over 1 million Kelvin, and the particles have an energy charge of more than 1 keV. There are actually two kinds of solar wind: slow and fast. This difference can be seen in comets. If you look closely at a picture of a comet, you will see that they often have two tails. One is straight and the other is more curved.

Solar wind speed online near the Earth, data for the last 3 days

Fast solar wind

It travels at 750 km/s and astronomers believe it originates from coronal holes, regions where magnetic field lines pierce the surface of the Sun.

slow solar wind

It has a speed of about 400 km / s, and comes from the equatorial belt of our star. The radiation reaches the Earth, depending on the speed, from several hours to 2-3 days.

The slow solar wind is wider and denser than the fast one, which creates a large, bright comet tail.

If not for the Earth's magnetic field, it would destroy life on our planet. However, the magnetic field around the planet protects us from radiation. The shape and size of the magnetic field is determined by the strength and speed of the wind.

SUNNY WIND- a continuous stream of plasma of solar origin, propagating approximately radially from the Sun and filling the solar system to the heliocentric. distances R ~ 100 a.u. e.s.v. formed during gas-dynamic expansion of the solar corona (cf. Sun) into interplanetary space. At high temperatures, which exist in the solar corona (1.5 * 10 9 K), the pressure of the overlying layers cannot balance the gas pressure of the corona matter, and the corona expands.

The first evidence of the existence of post. plasma flows from the Sun were obtained by L. Biermann in the 1950s. on the analysis of the forces acting on the plasma tails of comets. In 1957, J. Parker (E. Parker), analyzing the equilibrium conditions for the substance of the crown, showed that the crown cannot be under hydrostatic conditions. equilibrium, as previously assumed, but should expand, and this expansion, under the existing boundary conditions, should lead to acceleration of the coronal matter to supersonic velocities (see below). For the first time, a plasma flux of solar origin was registered at the Soviet spacecraft. apparatus "Luna-2" in 1959. The existence of post. The outflow of plasma from the Sun was proved as a result of many months of measurements on the Amer. space apparatus "Mariner-2" in 1962.

Wed S.'s characteristics are given in table. 1. Flows of S. in. can be divided into two classes: slow - with a speed of 300 km / s and fast - with a speed of 600-700 km / s. Fast streams come from regions of the solar corona, where the structure of the magnetic. field is close to radial. Some of these areas are coronal holes. Slow streams S. in. associated, apparently, with areas of the crown, in which there is, therefore, a tangential component of the magnetic field. fields.

Tab. one.- Average characteristics of the solar wind in Earth's orbit

Speed
Proton concentration
Proton temperature
Electron temperature
Magnetic field strength
Python Flux Density....	2.4*10 8 cm -2 *c -1
Kinetic energy flux density	0.3 erg*cm -2 *s -1

Tab. 2.- Relative chemical composition of the solar wind

	Relative content

	Relative content

In addition to the main the components of S. century - protons and electrons, in its composition particles, high-ionization are also found. ions of oxygen, silicon, sulfur, iron (Fig. 1). In the analysis of gases captured in foils exposed to the Moon, Ne and Ar atoms were found. Wed relative chem. S.'s composition is given in Table. 2. Ionization state of matter C. in. corresponds to that level in the corona where the recombination time is short compared to the expansion time Ionization measurements. temperature of ions S. century. make it possible to determine the electron temperature of the solar corona.

In S. century. differences are observed. types of waves: Langmuir, whistlers, ion-acoustic, magnetosonic, Alfven, etc. (see. Waves in plasma). Some of the Alfvén type waves are generated on the Sun, and some are excited in the interplanetary medium. The generation of waves smooths out the deviations of the particle distribution function from the Maxwellian and, in conjunction with the influence of the magnetic. field on the plasma leads to the fact that S. v. behaves like a continuum. Waves of the Alfvén type play an important role in the acceleration of small components of the solar wave. and in the formation of the proton distribution function. In S. century. contact and rotational discontinuities, which are characteristic of a magnetized plasma, are also observed.

Rice. 1. The mass spectrum of the solar wind. On the horizontal axis - the ratio of the mass of the particle to its charge, on the vertical - the number of particles registered in the energy window of the device for 10 s. Numbers with a "+" sign indicate the charge of the ion.

S.'s stream in. is supersonic in relation to the speeds of those types of waves, to-rye provide eff. energy transfer in S. century. (Alfven, sound and magnetosonic waves). Alvenovskoye and sound Mach number C.in. in Earth's orbit 7. When flowing around S. in. obstacles capable of effectively deflecting it (the magnetic fields of Mercury, Earth, Jupiter, Saturn or the conducting ionospheres of Venus and, apparently, Mars), an outgoing bow shock wave is formed. S. v. is decelerated and heated at the front of the shock wave, which allows it to flow around an obstacle. At the same time in S. century. a cavity is formed - the magnetosphere (own or induced), the shape and size of the swarm are determined by the balance of magnetic pressure. field of the planet and the pressure of the flowing plasma flow (see Fig. Earth's magnetosphere, planetary magnetospheres). In the case of interaction S. century. with a non-conducting body (for example, the Moon), a shock wave does not arise. The plasma flow is absorbed by the surface, and a cavity is formed behind the body, which is gradually filled with S.'s plasma.

The stationary process of corona plasma outflow is superimposed by nonstationary processes associated with solar flares. In strong flares, matter is ejected from the bottom. regions of the corona into the interplanetary medium. At the same time, a shock wave is also formed (Fig. 2), which gradually slows down, spreading in the S.'s plasma. The arrival of a shock wave to the Earth causes compression of the magnetosphere, after which the development of a magnetic field usually begins. storms (cf. magnetic variations).

Rice. 2. Propagation of an interplanetary shock wave and ejecta from a solar flare. The arrows show the direction of motion of the solar wind plasma, the lines without a label are the magnetic field lines.

Rice. 3. Types of solutions to the corona expansion equation. The speed and distance are normalized to the critical speed vc and the critical distance Rc. Solution 2 corresponds to the solar wind.

The expansion of the solar corona is described by a system of equations for the conservation of mass, momentum, and energy equations. Decisions that meet decomp. the nature of the change in speed with distance, are shown in fig. 3. Solutions 1 and 2 correspond to low velocities at the base of the corona. The choice between these two solutions is determined by the conditions at infinity. Solution 1 corresponds to low coronal expansion rates and gives large pressures at infinity, i.e., it encounters the same difficulties as the static model. crowns. Solution 2 corresponds to the passage of the expansion velocity through the values ​​of the speed of sound ( v to) on some critical distance R to and subsequent expansion at supersonic speed. This solution gives a vanishingly small value of the pressure at infinity, which makes it possible to match it with the low pressure of the interstellar medium. Yu. Parker called the course of this type S. century. Critical the point is above the surface of the Sun, if the temperature of the corona is less than a certain critical value. values , where m is the mass of the proton, is the adiabatic index, is the mass of the Sun. On fig. 4 shows the change in expansion rate with heliocentric. distance depending on the temperature isothermal. isotropic corona. Subsequent models of S. in. take into account variations in the coronal temperature with distance, the two-fluid nature of the medium (electron and proton gases), thermal conductivity, viscosity, non-spherical. the nature of the expansion.

Rice. 4. Solar wind velocity profiles for the isothermal corona model at various values ​​of coronal temperature.

S. v. provides the main the outflow of thermal energy of the corona, since heat transfer to the chromosphere, el-magn. corona radiation and electronic thermal conductivity S. v. insufficient to establish the thermal balance of the corona. Electronic thermal conductivity provides a slow decrease in the temperature of S. century. with distance. S. v. does not play any significant role in the energy of the Sun as a whole, since the energy flux carried away by it is ~ 10 -7 luminosity Sun.

S. v. carries the coronal magnetic field with it into the interplanetary medium. field. The lines of force of this field frozen into the plasma form the interplanetary magnetic field. field (MMP). Although the intensity of the IMF is small and its energy density is approx. 1% of the density of the kinetic. energy of S. century, it plays an important role in the thermodynamics of S. century. and in the dynamics of S.'s interactions. with bodies solar system, as well as S.'s flows. between themselves. Combination of S.'s expansion. with the rotation of the Sun leads to the fact that the magn. the lines of force frozen into the S. century have a shape close to the spiral of Archimedes (Fig. 5). Radial B R and azimuthal components of the magnetic. the fields change differently with distance near the plane of the ecliptic:

where - ang. sun rotation speed and- the radial component of the speed S. v., index 0 corresponds to the initial level. At a distance of the Earth's orbit, the angle between the direction of the magnetic. fields and R about 45°. At large L magn. the field is almost perpendicular to R.

Rice. 5. The shape of the field line of the interplanetary magnetic field. is the angular velocity of the Sun, and is the radial component of the plasma velocity, R is the heliocentric distance.

S. v., arising over the regions of the Sun with decomp. magnetic orientation. fields, forms flows with differently oriented IMF. Separation of the observed large-scale structure of S. v. into an even number of sectors with dec. the direction of the radial component of the IMF called. interplanetary sector structure. Characteristics of S. in. (speed, temp-pa, concentration of particles, etc.) also in cf. change regularly in the cross section of each sector, which is associated with the existence of a fast S. flow within the sector. Sector boundaries are usually located within the slow flow of S. at. Most often, 2 or 4 sectors are observed, rotating with the Sun. This structure which is formed at S.'s pulling out of century. large scale magnet. field of the crown, can be observed for several. revolutions of the sun. The sectoral structure of the IMF is a consequence of the existence of a current sheet (TS) in the interplanetary medium, which rotates together with the Sun. TS creates a magnetic surge. fields - the radial components of the IMF have different signs on different sides of the TS. This TS, predicted by H. Alfven, passes through those parts of the solar corona, which are associated with active regions on the Sun, and separates these regions from decomp. signs of the radial component of the solar magnet. fields. The TS is located approximately in the plane of the solar equator and has a folded structure. The rotation of the Sun leads to the twisting of the CS folds into a spiral (Fig. 6). Being near the plane of the ecliptic, the observer turns out to be either above or below the CS, due to which he falls into sectors with different signs of the IMF radial component.

Near the Sun in the N. century. there are longitudinal and latitudinal velocity gradients due to the difference in the velocities of fast and slow streams. As you move away from the Sun and steepen the boundary between the flows in the N. century. radial velocity gradients arise, which lead to the formation collisionless shock waves(Fig. 7). First, a shock wave is formed, propagating forward from the boundary of the sectors (direct shock wave), and then a reverse shock wave is formed, propagating towards the Sun.

Rice. 6. Shape of the heliospheric current sheet. Its intersection with the plane of the ecliptic (inclined to the equator of the Sun at an angle of ~ 7°) gives the observed sectoral structure of the interplanetary magnetic field.

Rice. 7. Structure of the sector of the interplanetary magnetic field. The short arrows show the direction of the solar wind plasma flow, the lines with arrows show the magnetic field lines, the dash-dotted line shows the sector boundaries (the intersection of the figure plane with the current sheet).

Since the shock wave velocity is less than the SW velocity, the plasma carries away the reverse shock wave in the direction away from the Sun. Shock waves near sector boundaries are formed at distances of ~1 AU. e. and can be traced to distances of several. a. e. These shock waves, like interplanetary shock waves from solar flares and circumplanetary shock waves, accelerate particles and are thus a source of energetic particles.

S. v. extends to distances of ~100 AU. That is, where the pressure of the interstellar medium balances the dynamic. S.'s pressure The cavity swept up by S. in. in the interstellar medium, forms the heliosphere (see. interplanetary environment).Expanding S. in. together with the magnet frozen into it. field prevents the penetration of galactic into the solar system. space rays of low energies and leads to variations in cosmic. beams of high energy. A phenomenon analogous to S. V. has also been discovered in certain other stars (cf. Stellar wind).

Lit.: Parker E. N., Dynamic processes in the interplanetary medium, trans. from English, M., 1965; B a n d t J., sunny wind, per. from English, M., 1973; Hundhausen, A., Coronal expansion and solar wind, transl. from English, M., 1976. O. L. Weisberg.

Solar wind and Earth's magnetosphere.

Sunny wind ( solar wind) is a stream of mega-ionized particles (mainly helium-hydrogen plasma) flowing from the solar corona at a speed of 300-1200 km/s into the surrounding space. It is one of the main components of the interplanetary medium.

Many natural phenomena are associated with the solar wind, including space weather phenomena such as magnetic storms and auroras.

The concepts of "solar wind" (a stream of ionized particles flying from the Sun to 2-3 days) and "sunshine" (a stream of photons flying from the Sun to the Earth in an average of 8 minutes 17 seconds) should not be confused. In particular, it is the effect of sunlight pressure (and not wind) that is used in the projects of the so-called solar sails. A form of engine for using an impulse of solar wind ions as a thrust source - an electric sail.

Story

The existence of a constant stream of particles flying from the Sun was first proposed by the British astronomer Richard Carrington. In 1859, Carrington and Richard Hodgson independently observed what was later called a solar flare. The following day, a geomagnetic storm occurred, and Carrington suggested a connection between these phenomena. Later, George Fitzgerald suggested that matter is periodically accelerated by the Sun and reaches the Earth in a few days.

In 1916, the Norwegian explorer Christian Birkeland wrote: "From a physical point of view, it is most probable that the rays of the sun are neither positive nor negative, but both." In other words, the solar wind is made up of negative electrons and positive ions.

Three years later, in 1919, Friederik Lindemann also suggested that particles of both charges, protons and electrons, come from the Sun.

In the 1930s, scientists determined that the temperature of the solar corona must reach a million degrees, since the corona remains bright enough at a great distance from the Sun, which is clearly visible during solar eclipses. Later spectroscopic observations confirmed this conclusion. In the mid-1950s, British mathematician and astronomer Sidney Chapman determined the properties of gases at such temperatures. It turned out that the gas becomes an excellent conductor of heat and should dissipate it into space beyond the Earth's orbit. At the same time, German scientist Ludwig Biermann became interested in the fact that comet tails always point away from the Sun. Biermann postulated that the Sun emits a constant stream of particles that pressurize the gas surrounding the comet, forming a long tail.

In 1955, Soviet astrophysicists S. K. Vsekhsvyatsky, G. M. Nikolsky, E. A. Ponomarev and V. I. Cherednichenko showed that an extended corona loses energy to radiation and can be in a state of hydrodynamic equilibrium only with a special distribution of powerful internal energy sources. In all other cases, there must be a flow of matter and energy. This process serves as a physical basis for an important phenomenon - the "dynamic corona". The magnitude of the flux of matter was estimated from the following considerations: if the corona were in hydrostatic equilibrium, then the heights of a homogeneous atmosphere for hydrogen and iron would be related as 56/1, that is, iron ions should not be observed in the far corona. But it's not. Iron glows throughout the corona, with FeXIV observed in higher layers than FeX, although the kinetic temperature is lower there. The force that maintains the ions in a "suspended" state can be the momentum transmitted during collisions by the ascending proton flux to the iron ions. From the condition of the balance of these forces, it is easy to find the flux of protons. It turned out to be the same as that followed from the hydrodynamic theory, subsequently confirmed by direct measurements. For 1955, this was a significant achievement, but no one then believed in the "dynamic crown".

Three years later, Eugene Parker concluded that the hot current from the Sun in Chapman's model and the stream of particles blowing away cometary tails in Biermann's hypothesis are two manifestations of the same phenomenon, which he called "solar wind". Parker showed that even though the solar corona is strongly attracted by the Sun, it conducts heat so well that it remains hot at great distances. Since its attraction weakens with distance from the Sun, a supersonic outflow of matter into interplanetary space begins from the upper corona. Moreover, Parker was the first to point out that the effect of weakening gravity has the same effect on the hydrodynamic flow as the Laval nozzle: it produces a transition of the flow from the subsonic to the supersonic phase.

Parker's theory has been heavily criticized. An article submitted in 1958 to the Astrophysical Journal was rejected by two reviewers and only thanks to the editor, Subramanyan Chandrasekhar, made it to the pages of the journal.

However, in January 1959, the first direct measurements of the characteristics of the solar wind (Konstantin Gringauz, IKI RAS) were carried out by the Soviet Luna-1, using a scintillation counter and a gas ionization detector installed on it. Three years later, the same measurements were carried out by the American Marcia Neugebauer using data from the Mariner-2 station.

Yet the acceleration of the wind to high speeds was not yet understood and could not be explained from Parker's theory. The first numerical models of the solar wind in the corona using the equations of magnetohydrodynamics were created by Pneumann and Knopp in 1971.

In the late 1990s, using the Ultraviolet Coronal Spectrometer ( Ultraviolet Coronal Spectrometer (UVCS) ) observations were made on board of the regions where the fast solar wind originated at the solar poles. It turned out that the wind acceleration is much greater than expected from purely thermodynamic expansion. Parker's model predicted that the wind speed becomes supersonic at 4 solar radii from the photosphere, and observations have shown that this transition occurs much lower, at about 1 solar radii, confirming that there is an additional mechanism for accelerating the solar wind.

Characteristics

The heliospheric current sheet is the result of the influence of the Sun's rotating magnetic field on the plasma in the solar wind.

Due to the solar wind, the Sun loses about one million tons of matter every second. The solar wind consists mainly of electrons, protons, and helium nuclei (alpha particles); the nuclei of other elements and non-ionized particles (electrically neutral) are contained in a very small amount.

Although the solar wind comes from the outer layer of the Sun, it does not reflect the real composition of the elements in this layer, since as a result of differentiation processes, the abundance of some elements increases and some decreases (FIP effect).

The intensity of the solar wind depends on changes in solar activity and its sources. Long-term observations in the Earth's orbit (about 150 million km from the Sun) have shown that the solar wind is structured and is usually divided into calm and disturbed (sporadic and recurrent). Calm flows, depending on the speed, are divided into two classes: slow(approximately 300-500 km / s near the Earth's orbit) and fast(500-800 km/s near the Earth's orbit). Sometimes the region of the heliospheric current sheet, which separates regions of different polarity of the interplanetary magnetic field, is referred to as a stationary wind, and is close in its characteristics to a slow wind.

slow solar wind

The slow solar wind is generated by the "calm" part of the solar corona (the region of coronal streamers) during its gas-dynamic expansion: at a corona temperature of about 2 10 6 K, the corona cannot be in hydrostatic equilibrium, and this expansion, under the existing boundary conditions, should lead to acceleration of the matter to supersonic speeds. The heating of the solar corona to such temperatures occurs due to the convective nature of heat transfer in the solar photosphere: the development of convective turbulence in the plasma is accompanied by the generation of intense magnetosonic waves; in turn, when propagating in the direction of decreasing the density of the solar atmosphere, sound waves are transformed into shock waves; shock waves are effectively absorbed by the material of the corona and heat it up to a temperature of (1-3) 10 6 K.

fast solar wind

Streams of the recurrent fast solar wind are emitted by the Sun for several months and have a return period of 27 days (the rotation period of the Sun) when observed from the Earth. These streams are associated with coronal holes - regions of the corona with a relatively low temperature (approximately 0.8 10 6 K), low plasma density (only a quarter of the density of quiet regions of the corona) and radial with respect to the Sun magnetic field.

Disturbed flows

Disturbed flows include the interplanetary manifestation of coronal mass ejections (CMEs), as well as compression regions ahead of fast CMEs (called Sheath in the English literature) and ahead of fast flows from coronal holes (called the Corotating interaction region - CIR in the English literature). About half of the cases of Sheath and CIR observations may have an interplanetary shock ahead of them. It is in perturbed solar wind types that the interplanetary magnetic field can deviate from the ecliptic plane and contain a southern field component, which leads to many effects of space weather (geomagnetic activity, including magnetic storms). Disturbed sporadic outflows were previously thought to be caused by solar flares, but sporadic outflows in the solar wind are now believed to be due to CMEs. At the same time, it should be noted that both solar flares and coronal mass ejections are associated with the same energy sources on the Sun and there is a statistical relationship between them.

According to the observation time of various large-scale solar wind types, fast and slow streams make up about 53%, the heliospheric current sheet 6%, CIR - 10%, CME - 22%, Sheath - 9%, and the ratio between the observation time of various types varies greatly in the solar cycle. activity.

Phenomena generated by the solar wind

Due to the high conductivity of the solar wind plasma, the solar magnetic field is frozen into the outflowing wind currents and is observed in the interplanetary medium in the form of an interplanetary magnetic field.

The solar wind forms the boundary of the heliosphere, due to which it prevents penetration into. The magnetic field of the solar wind significantly weakens the galactic cosmic rays coming from outside. A local increase in the interplanetary magnetic field leads to short-term decreases in cosmic rays, Forbush decreases, and large-scale field decreases lead to their long-term increases. Thus, in 2009, during the period of a protracted minimum of solar activity, the intensity of radiation near the Earth increased by 19% relative to all previously observed maxima.

The solar wind generates in the solar system, possessing a magnetic field, phenomena such as the magnetosphere, aurora and radiation belts of planets.