What is the cosmic wind. Sunny wind. The collapse of the idea of \u200b\u200ba static solar corona

sunny wind

- a continuous stream of plasma of solar origin, spreading approximately radially from the Sun and filling the solar system with itself to heliocentric. distances ~ 100 AU S.v. formed during gas dynamics. expansion into interplanetary space. At high temperatures, which exist in the solar corona (K), the pressure of the overlying layers cannot balance the gas pressure of the corona material, and the corona expands.

The first evidence of the existence of a constant plasma flow from the Sun was obtained by L. Birman (Germany) in the 1950s. analysis of the forces acting on the plasma tails of comets. In 1957, Yu. Parker (USA), analyzing the equilibrium conditions of the corona material, showed that the corona cannot be in hydrostatic conditions. equilibrium, as was previously assumed, but should expand, and this expansion under the existing boundary conditions should lead to the acceleration of coronal matter to supersonic speeds.

Average characteristics are given in table. 1. The plasma stream of solar origin was first recorded on the second Soviet cosmic plane. the Luna-2 rocket in 1959. The existence of a constant outflow of plasma from the Sun was proved in the result of many months of measurements by amer. AMC "Mariner-2" in 1962

Table 1. Average characteristics of the solar wind in orbit of the Earth

Speed	400 km / s
Proton density	6 cm -3
Proton temperature	TO
Electron temperature	TO
Magnetic field strength	E
Proton flux density	cm -2 s -1
Kinetic energy flux density	0.3 ergsm -2 s -1

Streams S.V. can be divided into two classes: slow - at a speed of km / s and fast - at a speed of 600-700 km / s. Fast currents come from areas of the corona where the magnetic field is close to radial. Some of these areas are . Slow Streams connected, apparently, with areas of the corona, where it means. tangential component of magn. fields.

In addition to the main components of S.v. - protons and electrons, it also contains β particles, highly ionized ions of oxygen, silicon, sulfur, iron (Fig. 1). In the analysis of gases trapped in the foils exposed on the Moon, Ne and Ar atoms were found. The average chem. composition S.v. given in table. 2.

Table 2. Relative chemical composition of the solar wind

Element	Relative content
H	0,96
3 He
4 He	0,04
O
Ne
Si
Ar
Fe

Ionization. state of matter corresponds to the level in the corona where the recombination time becomes small compared with the expansion time, i.e. on distance . Ionization measurements ion temperature S.v. allow determining the electronic temperature of the solar corona.

S.v. carries with him into the interplanetary medium coronal magn. field. The lines of force of this field frozen into the plasma form an interplanetary magnet. field (MMP). Although the tension of the IMF is low and its energy density is approx. 1% of kinetic energy of S.V., it plays a large role in the thermodynamics of S.V. and in the dynamics of interactions S.v. with bodies of the solar system and streams between themselves. Extension combination with the rotation of the Sun leads to the fact that the magn. power lyons frozen in northwest have a shape close to the spirals of Archimedes (Fig. 2). The radial and azimuthal components of the magn. fields near the ecliptic plane change with distance:
,
Where R - heliocentric. distance, is the angular velocity of rotation of the sun, u R - the radial component of the speed S.V., the index "0" corresponds to the initial level. At a distance of the Earth’s orbit, the angle between the directions of the magn. field and direction to the Sun, on large heliocentric. IMF distances are almost perpendicular to the direction to the Sun.

SV, arising over regions of the Sun with different orientations of magn. fields, forms flows in differently oriented IMFs - the so-called interplanetary magnetic field.

In S. St. various types of waves are observed: Langmuir, whistlers, ion-sound, magneto-sound, and others (see). Part of the waves is generated on the Sun, part is excited in the interplanetary medium. The generation of waves smooths the deviations of the particle distribution function from the Maxwellian one and leads to the fact that S. behaves like a continuous medium. Alfven-type waves play a large role in the acceleration of small components and in the formation of a proton distribution function. In S. St. Contact and rotational discontinuities, which are characteristic for magnetized plasma, are also observed.

Stream S.V. appr. supersonic with respect to the speed of those types of waves, which ensure efficient energy transfer to the SV (Alfven, sound and magnetosonic waves), Alfven and sound Mach numbers S.v. in orbit of the earth. When dooming S.v. obstacles that can effectively deflect S.v. (magnetic fields of Mercury, Earth, Jupiter, Sturn or the conducting ionospheres of Venus and, apparently, Mars), a head departing shock wave is formed. S.v. it brakes and heats up at the front of the shock wave, which allows it to flow around an obstacle. Moreover, in St. a cavity is formed - the magnetosphere (intrinsic or induced), the shape and size of the swarm is determined by the pressure balance of the magn. field of the planet and the pressure of the streamlined plasma flow (see). The layer of heated plasma between the shock wave and the streamlined obstacle is called. transitional area. The temperatures of ions at the front of a shock wave can increase by 10–20 times, electrons — by 1.5–2 times. Shock wave , the thermalization of the flow is ensured by collective plasma processes. The thickness of the shock wave front is ~ 100 km and is determined by the slew rate (magnetosonic and / or lower hybrid) during the interaction of the incident flux and part of the ion flux reflected from the front. In the case of interaction S.v. a shock wave does not occur with a non-conductive body (Moon): the plasma flow is absorbed by the surface, and gradually forms behind the body. cavity.

Unsteady processes associated with are superimposed on the stationary process of the outflow of the plasma of the corona. During strong solar flares, matter is ejected from the lower regions of the corona into the interplanetary medium. At the same time, a shock wave is also formed (Fig. 3), the edge gradually slows down when moving through the plasma S.v. The arrival of a shock wave to the Earth leads to a compression of the magnetosphere, after which the development of magn. storms.

An equation describing the expansion of the solar corona can be obtained from the system of equations for the conservation of mass and angular momentum. The solutions of this equation describing the different nature of the change in speed with distance are shown in Fig. 4. Decisions 1 and 2 correspond to low speeds at the base of the crown. The choice between these two solutions is determined by conditions at infinity. Solution 1 corresponds to low expansion rates of the corona ("solar breeze", according to J. Chamberlain, USA) and gives large values \u200b\u200bof pressure at infinity, i.e. meets the same difficulties as the static model. crowns. Solution 2 corresponds to the transition of the expansion rate through the value of the speed of sound ( v K) on some rum critical. distance R K and subsequent expansion at supersonic speed. This solution gives a vanishingly low pressure at infinity, which allows it to be matched with a low pressure of the interstellar medium. Parker called the current of this type the solar wind. Critical the point is above the surface of the Sun, if the temperature of the corona is less than a certain critical. values \u200b\u200bwhere m - proton mass, - adiabatic index. In fig. 5 shows the change in expansion rate with heliocentric. distance depending on the temperature isothermal. isotropic corona. Subsequent models take into account variations in the coronal temperature with distance, a two-fluid medium character (electron and proton gases), thermal conductivity, viscosity, non-spherical expansion. Approach to the substance how to a continuous medium is justified by the presence of IMF and the collective nature of the interaction of plasma S.V., due to various types of instabilities. S.v. provides the main outflow of thermal energy of the corona, as heat transfer to the chromosphere, electromagnet. emission of strongly ionized corona material and electronic thermal conductivity insufficient to establish the term. crown balance. Electronic thermal conductivity provides a slow decrease in temperature S.v. with distance. S.v. does not play any noticeable role in the energy of the sun as a whole, because the energy flow carried away by it is ~ 10 -8

Constant radial plasma flux of the sun. corona in interplanetary production. The flow of energy coming from the bowels of the Sun heats the plasma of the corona to 1.5–2 million K. heating is not balanced by the loss of energy due to radiation, because the corona is small. Excessive energy means. C. degrees are carried away by degrees. (\u003d 1027-1029 erg / s). Corona, i.e., is not in hydrostatic. equilibrium, it is constantly expanding. By composition C. century does not differ from the plasma of the corona (C. century contains hl. arr. protons, els, a few helium nuclei, oxygen ions, silicon, sulfur, iron). At the base of the corona (10 thousand km from the solar photosphere), the particles are of the radial order of hundreds m / s, at a distance of several. sun of radii, it reaches the speed of sound in a plasma (100-150 km / s), at the Earth’s orbit the speed of protons is 300-750 km / s, and their spaces. - from several. h to several. tens of hours in 1 cm3. With the help of interplanetary space. stations it was established that up to the orbit of Saturn, the flux density of CC C. in. decreases according to the law (r0 / r) 2, where r is the distance from the Sun, r0 is the initial level. S. century carries with it the loops of the lines of force of the sun. magn. fields, to-ry form interplanetary magn. . The combination of radial movement h-c S. century. with the rotation of the Sun gives these lines the shape of spirals. Large scale magn. The field in the vicinity of the Sun has the form of sectors in which the field is directed away from or towards the Sun. The size of the cavity occupied by C. century is not exactly known (its radius, apparently, is not less than 100 AU). At the borders of this cavity is dynamic. S. century should be balanced by interstellar gas pressure, galactic. magn. fields and galactic. cosm. rays. In the environs of the Earth, the collision of the flux of c. C. century with geomagn. field generates a stationary shock wave in front of the Earth’s magnetosphere (from the side of the Sun, Fig.).

S. century as if it flows around the magnetosphere, limiting its length in the ave. Changes in the intensity of S. century associated with outbreaks on the Sun, main cause disturbances geomagn. fields and magnetospheres (magn. storms).

Behind the Sun loses from S. century \u003d 2X10-14 part of its mass Msol. It is natural to consider that the outflow of the island, similar to the S. century, exists among other stars (""). It should be especially intense for massive stars (with mass \u003d several des. Des. Msols) and with a high surface temperature (\u003d 30-50 thousand K) and for stars with an extended atmosphere (red giants), because In the first case, the particles of a highly developed stellar corona possess high enough energy to overcome the attraction of the star, and in the second, parabolic is low. speed (escape speed; (see SPACE SPEEDS)). That means. mass losses with stellar wind (\u003d 10-6 Msol / year and more) can significantly affect the evolution of stars. In turn, the stellar wind creates “bubbles” of hot gas in the interstellar medium — sources of X-rays. radiation.

Physical Encyclopedic Dictionary. - M .: Soviet Encyclopedia. . 1983 .

SOLAR WIND - a continuous stream of plasma of solar origin, the 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 substances, and the corona expands.

The first evidence of the existence of the post. plasma flow from the sun received Birman (L. Biermann) in the 1950s. analysis of the forces acting on the plasma tails of comets. In 1957, Y. Parker (E. Parker), analyzing the equilibrium conditions of the substance of the corona, showed that the corona cannot be in hydrostatic conditions. Wed S.'s characteristics are given in table. 1. Streams S. century can be divided into two classes: slow - at a speed of 300 km / s and fast - at a speed of 600-700 km / s. Rapid flows emanate from the regions of the solar corona, where the structure of the magn. the field is close to radial. coronal holes. Slow Flows in. apparently connected with areas of the crown, in which means Tab. 1. - Average characteristics of the solar wind in orbit of the Earth

Speed
Proton concentration
Proton temperature
Electron temperature
Magnetic field strength
The density of the flow of pythons ....	2.4 * 10 8 cm -2 * c -1
Kinetic energy flux density	0.3 erg * cm -2 * s -1

Tab. 2.- The relative chemical composition of the solar wind

	Relative content

	Relative content

In addition to DOS. C. constituents of V. - protons and electrons, in its composition - particles are also found, Measurements of ionization. C. ion temperature allow to determine the electronic temperature of the solar corona.

In S. century decomp. types of waves: Langmuir, whistlers, ion-sound, Plasma waves). Part of the Alfven type waves are generated on the Sun, part - is excited in the interplanetary medium. Wave generation smooths the deviations of the particle distribution function from the Maxwellian one and in conjunction with the influence of magn. field to naplasm leads to the fact that C. century. behaves like a continuous medium. Waves of Alfven type play an important role in the acceleration of small components of C.

Fig. 1. Massive solar wind. The horizontal axis is the ratio of the mass of the particle to its charge, the vertical axis is the number of particles registered in the energy window of the device for 10 s. The numbers with the “+” sign indicate the charge of the ion.

Flow S. century is supersonic with respect to the speeds of those types of waves, which ensure eff. energy transfer in C. century (Alfven, sound). Alfven and sound Mach number S. in. 7. When flowing around S. century. obstacles that can effectively deflect it (the magnetic fields of Mercury, Earth, Jupiter, Saturn or the conducting ionospheres of Venus and, apparently, Mars), a departing head shock wave is formed. waves that allow it to flow around an obstacle. Moreover, in C. century. a cavity is formed - the magnetosphere (intrinsic or induced), the shape and dimensions of the swarm are determined by the pressure balance of the magn. the fields of the planet and the pressure of the flowing plasma flow (see Magnetosphere, Earth, Magnetosphere of planets). In case of interaction of S. century with a non-conducting body (e.g. Moon) a shock wave does not occur. The plasma stream is absorbed by the surface, and behind the body a cavity is formed, gradually filled with plasma C. in.

Unsteady processes associated with flashes in the sun. With strong outbreaks, the emission of matter from the bottom. areas of the corona into the interplanetary medium. Magnetic variations).

Fig. 2. The propagation of interplanetary shock wave and ejection from the solar flare. The arrows show the direction of movement of the solar wind plasma,

Fig. 3. Types of solutions of the equation of expansion of the corona. Velocity and distances are normalized to the critical velocity v k and the critical distance R k. Solution 2 corresponds to the solar wind.

The expansion of the solar corona is described by the system of mass conservation uri, v k) on some critical. distance R to and subsequent expansion with supersonic speed. This solution gives a vanishingly low pressure at infinity, which allows it to be matched with a low pressure of the interstellar medium. The flow of this type, Yu. Parker named S. century. , where m is the mass of the proton, is the adiabatic exponent, is the mass of the Sun. In fig. 4 shows the change in expansion rate with heliocentric. thermal conductivity, viscosity,

Fig. 4. Solar wind velocity profiles for the isothermal corona model at various coronal temperatures.

S. century provides the main outflow of thermal energy of the corona, because heat transferring the chromosphere, e-magn. corona and electronic thermal conductivity in. insufficient to establish the heat balance of the crown. Electronic thermal conductivity provides a slow decrease in temperature S. century. with distance. luminosity of the sun.

S. century carries with him into the interplanetary medium coronal magn. field. The lines of force of this field frozen into the plasma form an interplanetary magnet. field (IMF). Although the intensity of the IMF is small and its energy density is about 1% of the kinetic density. C. energy, it plays an important role in thermodynamics. in. and in the dynamics of interactions S. century. with bodies of the solar system, as well as S.'s streams. between themselves. Combination of expansion of S. century with the rotation of the Sun leads to the fact that the magn. lines of force frozen in in the north century have the form, B R and the azimuthal components of magn. Fields change differently with distance near the ecliptic plane:

where is the angle. Sun rotation speed and - radial velocity component century., index 0 corresponds to the initial level. At a distance of the Earth’s orbit, the angle between the direction of the magn. fields and R about 45 °. With large L magn.

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

C. century arising over the regions of the Sun with decomp. Orientation Magn. fields, velocity, p-pa, particle concentration, etc.) also in cf. regularly vary in the cross section of each sector, which is associated with the existence of an intra-sector of fast flow S. century. The boundaries of the sectors are usually located within the slow-moving S. stream. Most often, 2 or 4 sectors are observed, rotating together with the Sun. This structure, which is formed by stretching S. century. large-scale magn. fields of the crown, can be observed for several. revolutions of the sun. The sector structure of the IMF is a consequence of the existence of the current sheet (TS) in the interplanetary medium, which rotates with the Sun. TS creates a jump magn. fields -radial IMF have different signs on different sides of the vehicle. This TC predicted by X. Alfven (N. Alfven) passes through those parts of the solar corona that are associated with active regions on the Sun and share these regions with dec. signs of the radial component of the solar magn. fields. TC 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 folds of the vehicle in a spiral (Fig. 6). Being near the ecliptic plane, the observer is higher, then lower than the TS, due to which it falls into sectors with different signs of the radial component of the IMF.

Near the Sun in the North century There are longitudinal and latitudinal velocity gradients, and collisionless shock waves (Fig. 7). First, a shock wave is formed, propagating forward from the boundary of the sectors (a direct shock wave), and then a back shock wave is formed, propagating to the Sun.

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

Fig. 7. The structure of the interplanetary magnetic field sector. The short arrows indicate the direction of the solar wind, the arrows indicate the lines of force of the magnetic field, and the dot-and-dot line indicate the boundaries of the sector (the intersection of the plane of the figure with the current sheet).

Since the speed of the shock wave is less than the speed of the second century, it carries away the reverse shock wave in the direction from the Sun. Shock waves near the boundaries of sectors are formed at distances of ~ 1 a. e. and are traceable to distances in several. and. e. These shock waves, as well as interplanetary shock waves from solar flares and near-planet shock waves, accelerate particles and, therefore, are a source of energetic particles.

S. century extends to distances of ~ 100 a. e., where the pressure of the interstellar medium balances the dynamic. pressure S. century The cavity swept S. century Interplanetary Medium). Expanding c. in. along with the magn. field prevents the penetration into the solar system of galaxies. cosmic rays of low energies and leads to cosmic rays of high energies. A phenomenon similar to S. century is found in certain other stars (see Stellar wind).

Lit .: Parker E.N., Dynamic in the interplanetary medium, O. L. Weissberg.

Physical Encyclopedia. In 5 volumes. - M .: Soviet Encyclopedia. Editor-in-chief A. M. Prokhorov. 1988 .

See what "SUN WIND" is in other dictionaries:

SUNNY WIND, a solar corona plasma stream filling the solar system up to a distance of 100 astronomical units from the sun, where the pressure of the interstellar medium balances the dynamic pressure of the stream. The basic composition of protons, electrons, nuclei ... Modern Encyclopedia

SOLAR WIND, a steady stream of charged particles (mainly protons and electrons), accelerated by the high temperature of the solar CORONA to speeds large enough so that the particles overcome the gravity of the Sun. Solar wind deflects ... Scientific and technical encyclopedic dictionary

The atmosphere of the Sun is 90% hydrogen. The part farthest from the surface is called the corona of the sun; it is clearly visible at total solar eclipses. The temperature of the corona reaches 1.5-2 million K, and the corona gas is completely ionized. At such a plasma temperature, the thermal velocity of protons is of the order of 100 km / s, and of electrons is several thousand kilometers per second. To overcome solar attraction, an initial speed of 618 km / s, the second cosmic velocity of the Sun, is sufficient. Therefore, plasma constantly leaks from the solar corona into space. This flow of protons and electrons is called the solar wind.

Having overcome the attraction of the Sun, particles of the solar wind fly along direct paths. The speed of each particle almost does not change with distance, but it can be different. This speed depends mainly on the state of the solar surface, on the "weather" on the sun. On average, it is equal to v ≈ 470 km / s. The distance to the Earth from the solar wind passes in 3-4 days. In this case, the particle density in it decreases inversely with the square of the distance to the Sun. At a distance equal to the radius of the earth’s orbit, in 1 cm 3 there are on average 4 protons and 4 electrons.

The solar wind reduces the mass of our star - the Sun - by 10 9 kg per second. Although this number seems large on the Earth’s scale, it’s really small: a decrease in solar mass can be seen only at times thousands of times greater than the modern age of the Sun, which is approximately 5 billion years.

An interesting and unusual interaction of the solar wind with a magnetic field. It is known that charged particles usually move in a magnetic field H around a circle or along helical lines. This is true, however, only when the magnetic field is strong enough. More precisely, for the movement of charged particles in a circle, it is necessary that the magnetic field energy density H 2 / 8π be greater than the kinetic energy density of a moving plasma ρv 2/2. In the solar wind, the situation is reversed: the magnetic field is weak. Therefore, charged particles move in straight lines, and the magnetic field is not constant at the same time, it moves together with the stream of particles, as if carried away by this stream to the periphery of the solar system. The direction of the magnetic field throughout the interplanetary space remains the same as it was on the surface of the Sun at the time of the exit of the solar wind plasma.

When going around the equator of the Sun, the magnetic field, as a rule, changes its direction 4 times. The sun rotates: points on the equator make a revolution in T \u003d 27 days. Therefore, the interplanetary magnetic field is directed in spirals (see. Fig.), And the whole picture of this figure rotates after the rotation of the solar surface. The angle of rotation of the Sun changes as φ \u003d 2π / T. The distance from the Sun increases with the speed of the solar wind: r \u003d vt. Hence the equation of the spirals in Fig. has the form: φ \u003d 2πr / vT. At a distance of the Earth’s orbit (r \u003d 1.5 10 11 m), the angle of inclination of the magnetic field to the radius vector is, as is easily verified, 50 °. On average, such an angle is measured by spacecraft, but not quite close to the Earth. Near the planets, the magnetic field is arranged differently (see Magnetosphere).

Figure 1. Gelisfera

Figure 2. Solar flare.

The solar wind is a continuous stream of plasma of solar origin, propagating approximately radially from the Sun and filling the solar system with itself to heliocentric distances of about 100 AU Earth is formed during the gas-dynamic expansion of the solar corona into interplanetary space.

Average characteristics of the solar wind in the Earth’s orbit: speed 400 km / s, proton density 6 on 1, proton temperature 50 000 K, electron temperature 150 000 K, magnetic field strength 5 · Oersted. Solar wind flows can be divided into two classes: slow - at a speed of about 300 km / s and fast - at a speed of 600-700 km / s. The solar wind arising over regions of the Sun with different orientations of the magnetic field forms flows with differently oriented interplanetary magnetic fields - the so-called sector structure of the interplanetary magnetic fields.

The interplanetary sector structure is the separation of the observed large-scale structure of the solar wind into an even number of sectors with different directions of the radial component of the interplanetary magnetic field.

The characteristics of the solar wind (speed, temperature, particle concentration, etc.) also on average regularly change in the cross section of each sector, which is associated with the existence of a fast solar wind flow inside the sector. The boundaries of the sectors are usually located inside the slow flow of the solar wind. Most often, two or four sectors are observed, rotating with the sun. This structure, formed when the solar wind extends the large-scale magnetic field of the corona, can be observed for several revolutions of the sun. The sector structure is a consequence of the existence of the current sheet in the interplanetary medium, which rotates with the sun. The current layer creates a jump in the magnetic field: above the layer, the radial component of the interplanetary magnetic field has one sign, below it the other. The current layer 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 folds of the current sheet in a spiral (the so-called "ballerina effect"). Being near the plane of the ecliptic, the observer is either higher or lower than the current sheet, so that he falls into sectors with different signs of the radial component of the interplanetary magnetic field.

When the Solar wind flows around obstacles capable of effectively deflecting the Solar wind (magnetic fields of Mercury, Earth, Jupiter, Saturn or the conducting ionospheres of Venus and, apparently, Mars), a head departing shock wave is formed. The solar wind slows down and warms up at the front of the shock wave, which allows it to flow around an obstacle. In this case, a cavity is formed in the solar wind - the magnetosphere, the shape and size of which is determined by the balance of the pressure of the planet’s magnetic field and the pressure of the plasma flow around it. The thickness of the shock front is about 100 km. In the case of the interaction of the Solar wind with a non-conducting body (Moon), a shock wave does not occur: the plasma flow is absorbed by the surface, and behind the body a cavity is gradually filled by the plasma of the Solar wind.

Unsteady processes associated with solar flares are superimposed on the stationary process of corona plasma expiration. During strong solar flares, matter is ejected from the lower regions of the corona into the interplanetary medium. In addition, a shock wave is formed, which gradually slows down when moving through the plasma of the solar wind.

The arrival of a shock wave to the Earth leads to a compression of the magnetosphere, after which the development of a magnetic storm usually begins.

The solar wind extends to a distance of about 100 AU, where the pressure of the interstellar medium balances the dynamic pressure of the solar wind. The cavity swept by the solar wind in the interstellar medium forms the heliosphere. The solar wind, together with the magnetic field frozen into it, prevents the penetration of low-energy galactic cosmic rays into the solar system and leads to variations in high-energy cosmic rays.

A phenomenon similar to the solar wind is also found in some types of other stars (stellar wind).

The flow of solar energy, fueled by a thermonuclear reaction in its center, is fortunately extremely stable, unlike most other stars. Most of it is ultimately emitted by the thin surface layer of the Sun - the photosphere - in the form of electromagnetic waves in the visible and infrared range. The solar constant (the magnitude of the flow of solar energy in the Earth’s orbit) is 1370 W /. One can imagine that for every square meter of the Earth’s surface there is the power of one electric kettle. The Sun’s corona is located above the photosphere - a zone visible from the Earth only during solar eclipses and filled with rarefied and hot plasma with a temperature of millions of degrees.

This is the most unstable shell of the Sun, in which the main manifestations of solar activity, affecting the Earth, arise. The shaggy appearance of the corona of the sun shows the structure of its magnetic field - luminous plasma clots are elongated along the lines of force. Hot plasma flowing out of the corona forms a solar wind - an ion flux (consisting of 96% of hydrogen nuclei - protons and 4% of helium nuclei - alpha particles) and electrons, accelerating into interplanetary space at a speed of 400-800 km / s .

The solar wind stretches and carries away a solar magnetic field.

This is because the energy of the directed motion of the plasma in the outer corona is greater than the energy of the magnetic field, and the principle of freezing carries the field behind the plasma. The combination of such a radial outflow with the rotation of the Sun (and the magnetic field is “attached” to its surface) leads to the formation of a spiral structure of the interplanetary magnetic field - the so-called Parker spiral.

The solar wind and magnetic field fill the entire Solar system, and thus, the Earth and all other planets are actually located in the corona of the Sun, being affected not only by electromagnetic radiation, but also by the solar wind and solar magnetic field.

During a period of minimum activity, the configuration of the solar magnetic field is close to dipole and similar to the shape of the Earth’s magnetic field. When approaching a maximum of activity, the structure of the magnetic field is complicated for reasons that are not completely understood. One of the most beautiful hypotheses says that when the sun rotates, a magnetic field wraps around it, gradually plunging under the photosphere. Over time, during the time of the solar cycle, the magnetic flux accumulated below the surface becomes so large that the bundles of field lines begin to be pushed out.

The places where lines of force emerge form spots on the photosphere and magnetic loops in the corona, visible as regions of increased plasma luminescence in X-ray images of the Sun. The size of the field inside the sunspots reaches 0.01 Tesla, a hundred times larger than the field of the calm Sun.

Intuitively, the energy of a magnetic field can be associated with the length and number of lines of force: they are greater, the higher the energy. When approaching the solar maximum, the enormous energy accumulated in the field begins to be periodically explosively released, spending on acceleration and heating of the particles of the solar corona.

The sharp intense bursts of short-wave electromagnetic radiation of the Sun accompanying this process are called solar flares. On the Earth's surface, flares are recorded in the visible range as small increases in the brightness of individual sections of the solar surface.

However, the very first measurements performed on board spacecraft showed that the most noticeable effect of flares is a significant (up to hundreds of times) increase in the flux of solar x-ray radiation and energetic charged particles - solar cosmic rays.

During some flares, a significant amount of plasma and magnetic field is also ejected into the solar wind - the so-called magnetic clouds, which begin to expand rapidly into interplanetary space, retaining the shape of a magnetic loop with ends resting on the Sun.

The plasma density and the magnitude of the magnetic field inside the cloud are tens of times greater than the values \u200b\u200bof these parameters typical for a quiet time in the solar wind.

Despite the fact that up to 1025 joules of energy can be released during a large flash, the total increase in the energy flux to the solar maximum is small and amounts to only 0.1-0.2%.

VB Baranov, Moscow State University M.V. Lomonosov

The article considers the problem of supersonic expansion of the solar corona (solar wind). Four main problems are analyzed: 1) the causes of the outflow of plasma from the solar corona; 2) whether such expiration is uniform; 3) a change in the parameters of the solar wind with distance from the Sun; and 4) how the solar wind flows into the interstellar medium.

Introduction

Almost 40 years have passed since the American physicist E. Parker theoretically predicted the phenomenon, which was called the "solar wind" and which a couple of years later was experimentally confirmed by a group of Soviet scientist K. Greening with the help of instruments installed on Luna- 2 "and" Luna-3 ". The solar wind is a stream of fully ionized hydrogen plasma, that is, a gas consisting of electrons and protons of approximately the same density (quasi-neutrality condition), which moves with great supersonic speed from the sun. In the Earth’s orbit (one astronomical unit (a.e.) from the Sun), the velocity VE of this stream is approximately 400-500 km / s, the concentration of protons (or electrons) ne \u003d 10-20 particles in a cubic centimeter, and their temperature Te It is approximately 100,000 K (the electron temperature is slightly higher).

In addition to electrons and protons, interplanetary space was found to contain alpha particles (of the order of several percent), a small number of heavier particles, and also a magnetic field, the average value of the induction of which was in the orbit of the Earth of the order of several gammas (1

\u003d 10-5 G).

A bit of history related to the theoretical prediction of the solar wind

During the not-so-long history of theoretical astrophysics, it was believed that all the atmospheres of stars are in hydrostatic equilibrium, that is, in a state where the force of gravitational attraction of the star is balanced by the force associated with the pressure gradient in its atmosphere (with a change in pressure per unit distance r from the center stars). Mathematically, this equilibrium is expressed as an ordinary differential equation

(1)

where G is the gravitational constant, M * is the mass of the star, p is the pressure of the atmospheric gas,

- its mass density. If the temperature distribution T in the atmosphere is given, then from the equilibrium equation (1) and the equation of state for an ideal gas

(2)

where R is the gas constant, the so-called barometric formula is easily obtained, which in the particular case of constant temperature T will have the form

(3)

In formula (3), p0 is the pressure at the base of the star’s atmosphere (at r \u003d r0). This formula shows that for r

, that is, at very large distances from the star, the pressure p tends to a finite limit, which depends on the value of pressure p0.

Since it was believed that the solar atmosphere, like the atmosphere of other stars, is in a state of hydrostatic equilibrium, its state was determined by formulas similar to formulas (1), (2), (3). Given the unusual and yet incomprehensible phenomenon of a sharp increase in temperature from about 10,000 degrees on the surface of the Sun to 1,000,000 degrees in the solar corona, Chapman (see, for example,) developed the theory of a static solar corona, which should smoothly transfer to the interstellar medium surrounding the solar system.

However, in his pioneering work, Parker drew attention to the fact that the pressure at infinity, obtained from a formula of type (3) for a static solar corona, turns out to be almost an order of magnitude greater than the pressure value that was estimated for interstellar gas based on observations. To eliminate this discrepancy, Parker suggested that the solar corona is not in a state of static equilibrium, but is continuously expanding into the interplanetary medium surrounding the Sun. Moreover, instead of the equilibrium equation (1), he proposed using the hydrodynamic equation of motion of the form

(4)

where in the coordinate system associated with the Sun, the value V represents the radial velocity of the plasma. Under

mass of the sun is meant.

For a given temperature distribution T, the system of equations (2) and (4) has solutions of the type shown in Fig. 1. In this figure, a denotes the speed of sound, and r * is the distance from the origin at which the gas velocity is equal to the speed of sound (V \u003d a). Obviously, only curves 1 and 2 in Fig. 1 have physical meaning for the problem of gas outflow from the Sun, since curves 3 and 4 have non-unique values \u200b\u200bof velocity at each point, and curves 5 and 6 correspond to very high speeds in the solar atmosphere, which is not observed with telescopes. Parker analyzed the conditions under which a solution corresponding to curve 1 is realized in nature. He showed that in order to match the pressure obtained from such a solution with the pressure in the interstellar medium, the case of a gas transition from a subsonic flow is most real (at r< r*) к сверхзвуковому (при r > r *), and called this flow the solar wind. However, this statement was disputed in the work by Chamberlain, who considered the most realistic solution to be consistent with curve 2, which describes the subsonic “solar breeze” everywhere. Moreover, the first experiments on spacecraft (see, for example,) that discovered supersonic gas flows from the Sun did not seem, judging by the literature, Chamberlain reliable enough.

Fig. 1. Possible solutions of the one-dimensional equations of gas dynamics for the velocity V of the gas flow from the surface of the Sun in the presence of gravitational force. Curve 1 corresponds to the solution for the solar wind. Here a is the speed of sound, r is the distance from the Sun, r * is the distance at which the gas velocity is equal to the speed of sound, is the radius of the Sun.

The history of experiments in outer space brilliantly proved the correctness of Parker's ideas about the solar wind. Detailed material on the theory of solar wind can be found, for example, in a monograph.

Ideas of a uniform outflow of plasma from the solar corona

From the one-dimensional equations of gas dynamics, one can obtain a well-known result: in the absence of mass forces, the spherically-symmetric flow of gas from a point source can be either subsonic or supersonic everywhere. The presence of gravitational force in equation (4) (the right-hand side) leads to the appearance of solutions like curve 1 in Fig. 1, that is, with the transition through the speed of sound. Let us draw an analogy with the classical flow in the Laval nozzle, which is the basis of all supersonic jet engines. Schematically, this flow is shown in Fig. 2.

Fig. 2. Flow pattern in the Laval nozzle: 1 - a tank, called a receiver, into which very hot air is supplied at a low speed, 2 - the region of geometric compression of the channel to accelerate the subsonic gas flow, 3 - the region of geometric expansion of the channel to accelerate the supersonic flow.

A gas heated to a very high temperature is supplied to tank 1, called the receiver, at a very low speed (the internal energy of the gas is much greater than its kinetic energy of directional movement). By geometrically compressing the channel, the gas accelerates in region 2 (subsonic flow) until its speed reaches the speed of sound. To further accelerate it, it is necessary to expand the channel (region 3 of the supersonic flow). Across the entire flow region, gas accelerates due to its adiabatic (without heat input) cooling (the internal energy of chaotic motion transforms into the energy of directional motion).

In the problem of solar wind formation under consideration, the role of the receiver is played by the solar corona, and the role of the walls of the Laval nozzle by the gravitational force of solar attraction. According to Parker's theory, the transition through the speed of sound should occur somewhere at a distance of several solar radii. However, an analysis of the solutions obtained in the theory showed that the temperature of the solar corona is not enough for its gas to accelerate to supersonic speeds, as is the case in the theory of the Laval nozzle. There must be some additional source of energy. At present, such a source is considered to be the dissipation of wave motions always present in the solar wind (sometimes called plasma turbulence) superimposed on the average flow, and the flow itself is no longer adiabatic. A quantitative analysis of such processes still requires its study.

Interestingly, ground-based telescopes detect magnetic fields on the surface of the Sun. The average value of their magnetic induction B is estimated at 1 G, although in individual photospheric formations, for example, spots, the magnetic field can be orders of magnitude larger. Since plasma is a good conductor of electricity, it is natural that solar magnetic fields interact with its currents from the Sun. In this case, a purely gas-dynamic theory gives an incomplete description of the phenomenon under consideration. The influence of a magnetic field on the solar wind can only be considered within the framework of a science called magnetic hydrodynamics. What are the results of such considerations? According to pioneering work in this direction (see also), the magnetic field leads to the appearance of electric currents j in the solar wind plasma, which, in turn, leads to the appearance of the ponderomotive force j x B, which is directed in the direction perpendicular to the radial direction. As a result, the tangential velocity component appears in the solar wind. This component is almost two orders of magnitude less radial, but it plays a significant role in the removal of the moment of momentum from the Sun. It is believed that the latter circumstance can play a significant role in the evolution not only of the Sun, but also of other stars in which a "stellar wind" is detected. In particular, to explain the sharp decrease in the angular velocity of stars of the late spectral class, the hypothesis of the transfer of rotational moment to the planets forming around them is often used. The considered mechanism for the loss of the angular momentum of the Sun through the outflow of plasma from it opens up the possibility of revising this hypothesis.