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"Life with a star" – part 1: solar activity / SurprizingFacts

The night from the 1st to the 2nd of September, 1859 marked the largest polar aurora, in the history of astronomical observations – its Could be observed throughout the Earth. In the circumpolar regions, with its light, it was possible to read, it was so bright that it woke gold-diggers in the Rocky Mountains. Most telegraphs in Europe and North America were out of order, and on telegraph poles – witnesses observed sparks. Evaluation of the consequences of such an event (if it is in the modern world, with centralized electric grids) gives the magnitude of the damage in 0,6-2,6 trillion dollars, only for the United States. Such was the most destructive manifestation of cosmic weather at the moment, fixed by mankind.

In the first part of the article – I will describe the phenomena of solar activity that underlie "cosmic weather" and for this, in turn – we need to go deeper into the structure of the Sun, looking like this:

The solar core – occupies the zone from the center to 0.25 of the radius of the Sun. Here is the zone with the maximum temperature (about 15 million K), pressure (about 250 billion atmospheres), and density (reaching 150 g / cm 3 ). Since the rate of thermonuclear reactions strongly depends on temperature – the main part of the energy release in the Sun, occurs precisely in this region. However, even at such rates, the rate of thermonuclear reactions is not very high (on the order of 275 Watt / m 3 ), therefore thermonuclear reactors, such as ITER – require an order of magnitude higher temperatures in order to have reasonable indicators for the volume / power ratio.

The zone of radiative transfer – extends from a depth of 0.25, to about 0.7 the radius of the Sun. It is called so – because the main way to transfer energy in it is the sequential emission and absorption of photons. This is a fairly calm zone, in which the main type of motion is rotational: the Sun makes about one revolution in 25.6 days along the equator line (for the observer on Earth, taking into account our rotation around the Sun – about 28 days), and for 33.5 Day – at the level of the poles. The radiant zone, in this case, has a roughly averaged (between these two) velocities.

Tahoklin is a transition region located between the radiant and convective zones, its thickness is about 0.04 of the radius of the Sun . In this region, there is a transition from radiant (quiet) heat transfer to convective (turbulent), and from "solid-state rotation" (when the layers rotate at a uniform frequency) to differential (differing in polar and equatorial regions)

The reasons for such a transition are as follows: at the boundary of about 0.7 the radius of the Sun, the gradual drop in temperature and pressure of the solar layers leads to the fact that the physical conditions no longer permit the maintenance of plasma atoms without electrons (singly ionized atoms in Orodes and doubly – helium). Accordingly, the photoelectric effect begins to act, and the substance ceases to be transparent. Radiation transfer loses its effectiveness, and convective heat transfer comes first.

The explanation of the source of the second effect is a much more complex task, and its solution has not been given to scientists for a long time. But in 2013, using the data of the Solar Dynamics Observatory, the connection between the convective motion on the Sun (which is of a chaotic nature on small scales) and the stable, differential rotation of the Sun was also shown:

The following factors are the key factors in understanding the processes taking place on the Sun:

1) The source of energy for the emergence of all processes recorded by us on the Sun is turbulent convection (and already its source is the temperature gradient between solar And the surface of the Sun through which this energy is emitted.)

2) Almost all matter on the Sun (with the exception of a certain fraction of hydrogen in the photosphere) is in a state of plasma. For this reason, energy transfer occurs due to the kinetic energy of the convective currents, and due to the electromagnetic field. In this case, the energy can freely transfer from one species to another (the motion of the plasma can generate a magnetic field, and in the other case the magnetic field can accelerate the plasma streams).

The convective zone Located at a distance of about 0.7 radius, and directly to the most visible surface. For lack of other possibilities, the transfer of heat from this level begins to occur due to the mixing of the layers (that is, convection, why, in fact, this zone was so named). It is this zone that is responsible for all the phenomena that are commonly called "solar activity."

The basic structure of the convective zone (and the visible "surface" of the Sun) – consists of pellets (typical Diameter of 1000 km, and the time of existence – from 8 to 20 minutes), and supergranules (30 thousand kilometers in size, and a lifetime of about a day). Granular structure – consists of light areas (where matter rises from the depths of the Sun) and dark spaces between them (where matter is respectively lowered). The vertical velocity of the matter is 1-2 km / s, the depth of the granules is hundreds and thousands of kilometers.

Sunspots are regions in Which strong magnetic fields prevent the convective movement of matter. Despite the name – "spots" they can be called with a lot of tension: the temperature inside them is 3000-4500 K. And their apparent blackness is explained by the temperature of the surrounding substance (averaging – 5780 K), and correspondingly much smaller light emission "spots "On an external background. Practically from the beginning of systematic observations of sunspots in the sun in 1749, they became the main evidence of the existence of the 11-year cycle of solar activity (therefore, the zero cycle, from which the current date is being taken, was chosen: it began in 1745):

To be more precise, the cycle has an average duration of about 11.2 years, and varies from 7 to 17 years (with the shorter the cycle, the greater the strength It has). The stage of growth in the cycle takes a shorter period of time (4.6 years, versus 6.7 years – on average at the stage of decline). At the beginning of the cycle, the spots appear at latitudes of about ± 35-40 °, then shift to ± 15 ° during the peak period, and towards the end of the cycle, most of them occur at latitudes of ± 5-8 ° (the so-called Spherer law):

This cycle in behavior and the number of spots – is associated with the 11-year cycle of the change in the magnetic poles of the Sun (the full cycle for reversal of north / south polarity takes 22 years respectively). However, this 22-year period (the Hale cycle) has not been widely known, since in addition to the reversal of polarity, he himself practically does not manifest himself.

The presence of statistics for 400+ years – suggested the existence of a secular solar cycle Activity (the so-called cycle Gleisberg – lasting in the interval of 70-100 years, with an average value of 87 years). But to really prove its presence – it was possible only with the advent of radiocarbon analysis: the fact is that during solar maximum periods the solar wind becomes denser, and the heliosphere of the Sun expands slightly (this was based on the sequence of messages about Voyager-1 output beyond the solar system: 1, 2, 3, 4), while the flow of galactic cosmic rays – is reduced, and with it – the production of radioactive carbon-14 in the upper layers of the atmosphere is reduced. Traces of these changes over the past 11 thousand years are found in ice cores and annual rings of trees:

Sunspots are often formed in groups, with the leading spot – having the same polarity as And the current polarity of the hemisphere, and the back – the opposite. A group of spots can exist from a few hours to several months (this is the basis for a long-term, 27-day forecast – when spots that make one revolution return to the same position as now).

Solar Torches – are peculiar "spots on the revolution": in this case, the magnetic field acts as a convection enhancer, which in turn raises the temperature and luminosity of the "surface" of the Sun.

Prominences – The formation of a bizarre form, in a stable state – I remind you These are the halves of the torus resting on the "surface" of the Sun:

This form is due to the magnetic field that is their source: the flow of matter moving along the magnetic lines – From the depths of the Sun, then – describes the arc and falls back to the Sun. Such fountains of matter – can exist up to months. They can contain a huge energy that can be allocated in two physical phenomena, which will be discussed below.


The sun, a major prominence and Jupiter with the Earth are on a scale

Solar flares are giant energy spikes (the largest of which is described at the beginning of this article). In the course of a typical outbreak, an energy of the order of 10 20 J (about 10 gigatons in the TNT equivalent) can be released, in large bursts – about 10 25 J (about 1 billion megatons). Their source is the reconnection of magnetic fields on the Sun (when two magnetic "rings" come into contact with one another and change their structure dramatically):

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Accurate evidence of this process – were received very recently. In the course of a solar flare, energy is released in the entire spectrum of electromagnetic radiation, most of it is radiated in the hard ultraviolet, as well as X-rays and gamma rays (this is due to the fact that the magnetic fields warm up the plasma to tens of millions of degrees during the reconnection process). Only a small part of the energy is released in the visible light range, so in the usual situation – they are not visible. But in the case of the Carrington event, a flash could be observed even with the unaided eye.

The intensity flashes are divided into five classes: A, B, C, M, X. Each succeeding class is ten times stronger than the previous one. Each class is divided into a linear scale from 1.0 to 9.9, in class X there is no upper limit: at the moment the most powerful flash recorded since 1957 (when extra-atmospheric observations began and the total power across the entire spectrum of radiation became possible) – occurred November 4, 2003, and according to the specified data, it had class X45.

Flash class The intensity in gamma rays is 0.5-8 Å, W m 2
A to 10 -7
B from 10 -7 to 10 -6
C from 10 -6 to 10 -5
M from 10 -5 to 10 -4
X more than 10 -4

Coronal mass ejections are accompanying flashes (but not always), the process of ejection of huge masses of matter (which is reflected in the name of this process). On average, the emissions are about one billion tons, and flow at a high speed (about 500 km / s). The source of such masses are prominences. In the process of reconnection of the magnetic field – magnetic lines rush from the sun to infinity, followed by the masses of plasma moving along them:

Coronal emission model

The latest computer models describe the processes taking place on the Sun with high accuracy – this allows us to hope that soon a period of accurate forecasts for space weather can be obtained not for 3 days – but for a much longer period.

Comparison of the model with the real coronal ejection

The photosphere is the visible "surface" of the Sun. It is approximately 300 km in thickness, and it is in it that most of the visible spectrum is emitted. The density of this layer is from 10 -8 to 10 -9 g / cm 3 . It is here that the minimum temperature of the Sun is reached – 4300 K, but the average temperature of this region is closer to the temperature in 5777 K:

Actually being an extension of the convective zone – the photosphere is visible (for us) Phenomena and the structure that exists in the convective zone (which is described above).

Chromosphere is a layer of about 10 thousand km thick, located between the photosphere and the crown. Here the pressure begins to drop sharply, and the temperature starts to rise again:

Due to the fact that the pressure in this layer is very low, its luminosity (despite the temperature rise) Hundreds of times less than the photosphere. For this reason, for the first time it was discovered due to lunar eclipses (when the light from the photosphere did not interfere with the observation of this layer). It is in this region of the sun that Helium was first discovered.

The chromosphere consists mainly of spicules – objects of oblong form, having several thousand kilometers in diameter, and about a thousand in depth:

Rising from the photosphere – they transfer matter to the upper layers of the Sun. Another component of the chromosphere is fibrils. They are vertical loops of matter, entrained by a magnetic field (by the type of prominences).

The crown – starts from the visible radius of the Sun, and extends to 10-20 its diameters. It consists of a very rarefied and unevenly distributed substance with a temperature exceeding one million kelvin.

The source of such a high corona temperature, according to the latest data, is the chromospheric spicules, which feed it with high-energy particles . The structure of the corona greatly depends on the period of solar activity: during the maxima, it has a spherical shape, during minima it is elongated along the equatorial direction:

Solar wind Is a stream of highly rarefied solar matter, with a temperature close to coronal, moving at high speed (on the Earth's orbit – its velocity is 300-400 km / s):

This Substance – accelerates the magnetic fields of the Sun (from this – such a high difference in speed between the equator And poles). The pressure it produces – is on the Earth's orbit 1-6 nPa (depending on the period of the 11-year cycle, and the presence of coronal emissions). By the solar wind, the Sun loses about 10 -14 M C (this is several orders of magnitude less than that it loses due to radiation).

In the second part of the article – about space weather, apparatuses exploring the Sun and services that monitor its condition.

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