In 1905, Einstein named the cause of terrestrial magnetism as one of the five main mysteries of contemporary physics.

Also in 1905, the French geophysicist Bernard Brunhes measured the magnetism of Pleistocene lava deposits in the southern department of Cantal. The magnetization vector of these rocks was almost 180 degrees with the planetary magnetic field vector (his compatriot P. David obtained similar results even a year earlier). Brunhes concluded that three-quarters of a million years ago, during an outpouring of lava, the direction of the geomagnetic field lines was opposite to the modern one. So the effect of inversion (reversal of polarity) of the Earth's magnetic field was discovered. In the second half of the 1920s, Brunhes' conclusions were confirmed by P. L. Mercanton and Monotori Matuyama, but these ideas were recognized only by the middle of the century.

We now know that the geomagnetic field has existed for at least 3.5 billion years, and during this time the magnetic poles exchanged places thousands of times (Brunhes and Matuyama studied the last reversal, which now bears their names). Sometimes the geomagnetic field retains its orientation for tens of millions of years, and sometimes for no more than five hundred centuries. The reversal process itself usually takes several millennia, and after its completion, the field strength, as a rule, does not return to its previous value, but changes by several percent.

The mechanism of geomagnetic reversal is not quite clear even today, and even a hundred years ago it did not allow a reasonable explanation at all. Therefore, the discoveries of Brunhes and David only reinforced Einstein's assessment - indeed, terrestrial magnetism was extremely mysterious and incomprehensible. But by that time it had been studied for over three hundred years, and in the 19th century such stars of European science as the great traveler Alexander von Humboldt, the brilliant mathematician Carl Friedrich Gauss and the brilliant experimental physicist Wilhelm Weber were engaged in it. So Einstein really looked at the root.

How many magnetic poles do you think our planet has? Almost everyone will say that two are in the Arctic and Antarctic. In fact, the answer depends on the definition of the concept of a pole. Intersection points are considered geographic poles. earth's axis with the surface of the planet. As the earth rotates like solid, there are only two such points and nothing else can be invented. But with magnetic poles, the situation is much more complicated. For example, a pole can be considered a small area (ideally again a point) where the magnetic lines of force are perpendicular to the earth's surface. However, any magnetometer registers not only the planetary magnetic field, but also the fields of local rocks, electric currents of the ionosphere, solar wind particles, and other additional sources of magnetism (and their average share is not so small, on the order of a few percent). The more accurate the device, the better it does this - and therefore it becomes more and more difficult to isolate the true geomagnetic field (it is called the main one), the source of which is located in the depths of the earth. Therefore, the coordinates of the pole, determined using direct measurement, are not stable even for a short period of time.

You can act differently and establish the position of the pole on the basis of certain models of terrestrial magnetism. In the first approximation, our planet can be considered a geocentric magnetic dipole, the axis of which passes through its center. At present, the angle between it and the earth's axis is 10 degrees (a few decades ago it was more than 11 degrees). With more accurate modeling, it turns out that the dipole axis is offset from the center of the Earth in the direction of the northwest Pacific Ocean by about 540 km (this is an eccentric dipole). There are other definitions as well.

But that is not all. The terrestrial magnetic field does not really have dipole symmetry and therefore has multiple poles, and in huge numbers. If we consider the Earth as a magnetic quadrupole, a quadrupole, we will have to introduce two more poles - in Malaysia and in the southern part of the Atlantic Ocean. The octupole model specifies the eight poles, and so on. The most advanced modern models of terrestrial magnetism operate with as many as 168 poles. It should be noted that only the dipole component of the geomagnetic field temporarily disappears during the inversion, while the others change much more weakly.

The poles are reversed

Many people know that the generally accepted names for the poles are exactly the opposite. There is a pole in the Arctic, to which the north end of the magnetic needle points, - therefore, it should be considered south (poles of the same name repel, opposite ones attract!). Likewise, the north magnetic pole is based at high latitudes in the southern hemisphere. However, traditionally we name the poles according to geography. Physicists have long agreed that the lines of force come out of the north pole of any magnet and enter the south. It follows from this that the lines of terrestrial magnetism leave the south geomagnetic pole and are drawn to the north. This is the convention, and it is not worth breaking it (it's time to recall the sad experience of Panikovsky!).

The magnetic pole, no matter how you define it, does not stand still. The north pole of the geocentric dipole in 2000 had coordinates of 79.5 N and 71.6 W, and in 2010 - 80.0 N and 72.0 W. The true North Pole (the one that physical measurements reveal) has shifted since 2000 from 81.0 N and 109.7 W to 85.2 N and 127.1 W. For almost the entire 20th century, he did not exceed 10 km per year, but after 1980 he suddenly began to move much faster. In the early 1990s, its speed exceeded 15 km per year and continues to grow.

As he told Popular Mechanics former leader Geomagnetic Laboratory of the Canadian Geological Survey Lawrence Newitt, now the true pole is migrating to the northwest, moving 50 km annually. If the vector of its movement does not change for several decades, then by the middle of the 21st century it will be in Siberia. According to a reconstruction made a few years ago by the same Newitt, in the 17th and 18th centuries, the north magnetic pole mainly shifted to the southeast, and only about 1860 turned to the northwest. The true south magnetic pole has been moving in the same direction for the last 300 years, and its average annual displacement does not exceed 10–15 km.

Where does the Earth's magnetic field come from? One of the possible explanations is simply striking. The Earth has an internal solid iron-nickel core, the radius of which is 1220 km. Since these metals are ferromagnetic, why not assume that the inner core has a static magnetization, which ensures the existence of the geomagnetic field? The multipolarity of terrestrial magnetism can be attributed to the asymmetry of the distribution of magnetic domains inside the core. The migration of the poles and the reversal of the geomagnetic field is more difficult to explain, but perhaps one can try.

However, nothing comes of it. All ferromagnets remain ferromagnets (that is, they retain spontaneous magnetization) only below a certain temperature - the Curie point. For iron, it is 768°C (for nickel, much lower), and the temperature of the Earth's inner core is much higher than 5000 degrees. Therefore, we have to part with the hypothesis of static geomagnetism. However, it is possible that in space there are cooled planets with ferromagnetic cores.

Let's consider another possibility. Our planet also has a liquid outer core approximately 2300 km thick. It consists of a melt of iron and nickel with an admixture of lighter elements (sulfur, carbon, oxygen, and possibly radioactive potassium - no one knows for sure). The temperature of the lower part of the outer core almost coincides with the temperature of the inner core, and in the upper zone at the boundary with the mantle it drops to 4400°C. Therefore, it is quite natural to assume that due to the rotation of the Earth, circular currents are formed there, which may be the cause of the emergence of terrestrial magnetism.

convective dynamo

“In order to explain the emergence of a poloidal field, it is necessary to take into account the vertical flows of matter in the nucleus. They are formed due to convection: a heated iron-nickel melt emerges from the lower part of the core towards the mantle. These jets are twisted by the Coriolis force like the air currents of cyclones. Updrafts rotate clockwise in the Northern Hemisphere and counter-clockwise in the Southern Hemisphere, explains University of California professor Gary Glatzmayer. - When approaching the mantle, the substance of the core cools down and begins a reverse movement in depth. The magnetic fields of the updrafts and downdrafts cancel each other out, and therefore the field is not established vertically. But in the upper part of the convection jet, where it forms a loop and moves horizontally for a short time, the situation is different. In the Northern Hemisphere, field lines that faced west before the convection ascent turn 90 degrees clockwise and orient themselves to the north. In the Southern Hemisphere, they turn counterclockwise from the east and also head north. As a result, a magnetic field is generated in both hemispheres, pointing from south to north. Although this is by no means the only possible explanation for the occurrence of the poloidal field, it is considered the most probable.

It was this scheme that geophysicists discussed about 80 years ago. They believed that the flows of the conductive liquid of the outer core, due to their kinetic energy, generate electric currents that envelop the earth's axis. These currents generate a magnetic field predominantly of the dipole type, the lines of force of which on the Earth's surface are elongated along the meridians (such a field is called poloidal). This mechanism is associated with the operation of a dynamo, hence its name.

The described scheme is beautiful and illustrative, but, unfortunately, it is erroneous. It is based on the assumption that the motion of matter in the outer core is symmetrical about the earth's axis. However, in 1933, the English mathematician Thomas Cowling proved a theorem according to which no axisymmetric flows can ensure the existence of a long-term geomagnetic field. Even if it appears, its age will be short, tens of thousands of times less than the age of our planet. We need a more complex model.

“We don't know exactly when terrestrial magnetism arose, but it could have happened shortly after the formation of the mantle and outer core,” says David Stevenson, one of the leading experts in planetary magnetism, professor at the California Institute of Technology. - To turn on the geodynamo, an external seed field is required, and not necessarily a powerful one. This role, for example, could be assumed by the magnetic field of the Sun or the fields of currents generated in the core due to the thermoelectric effect. Ultimately, this is not too important, there were enough sources of magnetism. In the presence of such a field and the circular motion of the flow of conductive fluid, the launch of an intraplanetary dynamo became simply inevitable.”

Magnetic protection

Monitoring of terrestrial magnetism is carried out using an extensive network of geomagnetic observatories, the creation of which began in the 1830s.

For the same purposes, ship, aviation and space instruments are used (for example, the scalar and vector magnetometers of the Danish Oersted satellite, which have been operating since 1999).

The geomagnetic field strength varies from approximately 20,000 nanotesla near the coast of Brazil to 65,000 nanotesla near the south magnetic pole. Since 1800, its dipole component has decreased by almost 13% (and by 20% since the middle of the 16th century), while its quadrupole component has slightly increased. Paleomagnetic studies show that for several millennia before the beginning of our era, the intensity of the geomagnetic field stubbornly climbed up, and then began to decline. Nevertheless, the current planetary dipole moment is significantly higher than its average value over the past hundred and fifty million years (in 2010, paleomagnetic measurements were published, indicating that 3.5 billion years ago, the Earth's magnetic field was twice as weak as the current one). This means that the entire history of human societies from the emergence of the first states to our time fell on the local maximum of the earth's magnetic field. It is interesting to think about whether this influenced the progress of civilization. Such an assumption ceases to seem fantastic, given that the magnetic field protects the biosphere from cosmic radiation.

And here is another circumstance that is worth noting. In the youth and even adolescence of our planet, all the substance of its core was in the liquid phase. The solid inner core formed relatively recently, perhaps as little as a billion years ago. When this happened, the convection currents became more ordered, resulting in a more stable operation of the geodynamo. Because of this, the geomagnetic field has gained in magnitude and stability. It can be assumed that this circumstance favorably affected the evolution of living organisms. In particular, the increase in geomagnetism has improved the protection of the biosphere from cosmic radiation and thus facilitated the emergence of life from the ocean to land.

Here is the generally accepted explanation for such a launch. Let, for simplicity, the seed field be almost parallel to the Earth's rotation axis (in fact, it is sufficient if it has a nonzero component in this direction, which is almost inevitable). The speed of rotation of the substance of the outer core decreases as the depth decreases, and due to its high electrical conductivity, the magnetic field lines move with it - as physicists say, the field is "frozen" into the medium. Therefore, the lines of force of the seed field will bend, moving forward at greater depths and lagging behind at shallower ones. Eventually they will stretch and deform so much that they will give rise to a toroidal field, circular magnetic loops that wrap around the earth's axis and point in opposite directions in the northern and southern hemispheres. This mechanism is called the w-effect.

According to Professor Stevenson, it is very important to understand that the toroidal field of the outer core arose due to the poloidal seed field and, in turn, gave rise to a new poloidal field observed at the earth's surface: "Both types of planetary geodynamo fields are interconnected and cannot exist without each other" .

15 years ago, Gary Glatzmeier, together with Paul Roberts, published a very beautiful computer model of the geomagnetic field: “In principle, to explain geomagnetism, there has long been an adequate mathematical apparatus - the equations of magnetohydrodynamics plus equations describing the force of gravity and heat flows inside the earth's core. Models based on these equations are very complex in their original form, but they can be simplified and adapted for computer calculations. That is exactly what Roberts and I did. A supercomputer run made it possible to construct a self-consistent description of the long-term evolution of the velocity, temperature, and pressure of the matter flows in the outer core and the evolution of magnetic fields associated with them. We also found that if we play the simulation over time intervals of the order of tens and hundreds of thousands of years, then geomagnetic field reversals inevitably occur. So in this respect, our model does a pretty good job of conveying the magnetic history of the planet. However, there is a problem that has not yet been resolved. The parameters of the substance of the outer core, which are included in such models, are still too far from real conditions. For example, we had to accept that its viscosity is very high, otherwise the resources of the most powerful supercomputers will not be enough. In fact, this is not so, there is every reason to believe that it almost coincides with the viscosity of water. Our current models are powerless to take into account the turbulence, which undoubtedly takes place. But computers are gaining momentum every year, and in ten years there will be much more realistic simulations.

“The work of the geodynamo is inevitably associated with chaotic changes in the flows of the iron-nickel melt, which turn into fluctuations in magnetic fields,” adds Professor Stevenson. - Inversions of the earth's magnetism are simply the strongest possible fluctuations. Since they are stochastic in nature, they can hardly be predicted in advance - in any case, we cannot.”

In recent days, a large amount of news on the Earth's magnetic field has appeared on scientific information sites. For example, the news that recent times it changes significantly, or that the magnetic field contributes to the leakage of oxygen from the earth's atmosphere, and even about the fact that cows orient themselves along the lines of the magnetic field in pastures. What is the magnetic field and how important is all of the above news?

The Earth's magnetic field is the area around our planet where magnetic forces. The question of the origin of the magnetic field has not yet been finally resolved. However, most researchers agree that the presence of the Earth's magnetic field is at least partly due to its core. The Earth's core consists of a solid inner and liquid outer parts. The rotation of the Earth creates constant currents in the liquid core. As the reader may remember from physics lessons, motion electric charges creates a magnetic field around them.

One of the most common theories explaining the nature of the field, the theory of the dynamo effect, assumes that convective or turbulent movements of a conducting fluid in the core contribute to self-excitation and maintaining the field in a stationary state.

The earth can be considered as a magnetic dipole. Its south pole is located at the geographic North Pole, and the north, respectively, at the South. In fact, the geographical and magnetic poles of the Earth do not coincide not only in "direction". The axis of the magnetic field is tilted with respect to the axis of rotation of the Earth by 11.6 degrees. Due to the fact that the difference is not very significant, we can use a compass. Its arrow points exactly to the south magnetic pole of the Earth and almost exactly to the geographic north. If the compass had been invented 720,000 years ago, it would have pointed to both the geographic and magnetic north poles. But more on that below.

The magnetic field protects the inhabitants of the Earth and artificial satellites from the harmful effects of cosmic particles. Such particles include, for example, ionized (charged) particles of the solar wind. The magnetic field changes the trajectory of their movement, directing the particles along the field lines. The need for a magnetic field for the existence of life narrows the range of potentially habitable planets (if we start from the assumption that hypothetically possible life forms are similar to earthly inhabitants).

Scientists do not exclude that some of the terrestrial planets do not have a metallic core and, accordingly, are devoid of a magnetic field. Until now, it was believed that the planets, consisting of solid rocks, like the Earth, contain three main layers: a solid crust, a viscous mantle, and a solid or molten iron core. In recent work, MIT scientists have proposed the formation of "rocky" planets without a core. If the theoretical calculations of researchers are confirmed by observations, then in order to calculate the probability of meeting humanoids in the Universe, or at least something resembling illustrations from a biology textbook, they will have to be rewritten.

Earthlings can also lose their magnetic protection. True, geophysicists cannot yet say exactly when this will happen. The fact is that the magnetic poles of the Earth are unstable. Periodically they change places. Not so long ago, researchers found that the Earth "remembers" the change of poles. An analysis of such "memories" showed that over the past 160 million years, magnetic north and south have changed places about 100 times. The last time this event happened about 720 thousand years ago.

The change of poles is accompanied by a change in the configuration of the magnetic field. In time " transition period"Significantly more cosmic particles that are dangerous to living organisms penetrate the Earth. One of the hypotheses explaining the disappearance of dinosaurs claims that the giant reptiles died out precisely during the next change of poles.

In addition to the "traces" of planned activities to change the poles, the researchers noticed dangerous shifts in the Earth's magnetic field. An analysis of the data on his condition over several years showed that in recent months they began to occur in him. Scientists have not recorded such sharp "movements" of the field for a very long time. The area of ​​concern to researchers is located in the South Atlantic Ocean. The "thickness" of the magnetic field in this region does not exceed a third of the "normal" one. Researchers have long paid attention to this "hole" in the Earth's magnetic field. The data collected over 150 years show that the field here has weakened by ten percent over this period.

At the moment it is difficult to say how this threatens humanity. One of the consequences of the weakening of the field strength may be an increase (albeit insignificant) in the oxygen content in the Earth's atmosphere. The connection between the Earth's magnetic field and this gas was established using the Cluster satellite system, a project of the European Space Agency. Scientists have found that the magnetic field accelerates oxygen ions and "throws" them into outer space.

Despite the fact that the magnetic field cannot be seen, the inhabitants of the Earth feel it well. Migratory birds, for example, find their way, focusing on it. There are several hypotheses that explain exactly how they feel the field. One of the latter suggests that birds perceive a magnetic field. Special proteins - cryptochromes - in the eyes of migratory birds are able to change their position under the influence of a magnetic field. The authors of the theory believe that cryptochromes can act as a compass.

In addition to birds, sea turtles use the Earth's magnetic field instead of GPS. And, as shown by the analysis of satellite photographs presented as part of the Google Earth project, cows. After studying photographs of 8510 cows in 308 regions of the world, scientists concluded that these animals are preferred (or from south to north). Moreover, the “reference points” for cows are not geographic, but precisely the magnetic poles of the Earth. The mechanism of the cows' perception of the magnetic field and the reasons for such a reaction to it remain unclear.

In addition to the listed remarkable properties, the magnetic field contributes. They arise as a result of abrupt field changes occurring in remote regions of the field.

The magnetic field has not been ignored by supporters of one of the "conspiracy theories" - the theory of lunar hoax. As mentioned above, the magnetic field protects us from cosmic particles. The "collected" particles accumulate in certain parts of the field - the so-called Van Alen radiation belts. Skeptics who do not believe in the reality of landings on the moon believe that during the flight through the radiation belts, the astronauts would receive a lethal dose of radiation.

The Earth's magnetic field is an amazing consequence of the laws of physics, a protective shield, landmark and creator of the auroras. Without it, life on Earth might look very different. In general, if there were no magnetic field, it would have to be invented.

Most of the planets in the solar system have magnetic fields to some extent.
A special branch of geophysics that studies the origin and nature of the Earth's magnetic field is called geomagnetism. Geomagnetism considers the problems of the emergence and evolution of the main, constant component of the geomagnetic field, the nature of the variable component (about 1% of the main field), as well as the structure of the magnetosphere - the uppermost magnetized plasma layers of the earth's atmosphere that interact with the solar wind and protect the Earth from penetrating cosmic radiation . An important task is to study the patterns of geomagnetic field variations, since they are caused by external influences associated primarily with solar activity.

It may be surprising, but today there is no single point of view on the mechanism of the origin of the magnetic field of the planets, although the magnetic hydrodynamo hypothesis, based on the recognition of the existence of a conductive liquid outer core, is almost universally recognized. Thermal convection, that is, the mixing of matter in the outer core, contributes to the formation of ring electric currents. The speed of movement of matter in the upper part of the liquid core will be somewhat less, and the lower layers - more relative to the mantle in the first case and solid core- in the second. Such slow currents cause the formation of annular (toroidal) electric fields closed in shape, which do not go beyond the core. Due to the interaction of toroidal electric fields with convective currents, a total magnetic field of a dipole nature arises in the outer core, the axis of which approximately coincides with the axis of rotation of the Earth. To “start” such a process, an initial, even if very weak, magnetic field is required, which can be generated by the gyromagnetic effect when a rotating body is magnetized in the direction of its axis of rotation.

Not the last role is played by the solar wind - the flow of charged particles, mainly protons and electrons coming from the Sun. For the Earth, the solar wind is a stream of charged particles in a constant direction, and this is nothing more than an electric current.

According to the definition of the direction of the current, it is directed in the direction opposite to the movement of negatively charged particles (electrons), i.e. from the Earth to the Sun. Particles that form the solar wind, having mass and charge, are carried away by the upper layers of the atmosphere in the direction of the Earth's rotation. In 1958, the Earth's radiation belt was discovered. This is a huge zone in space, covering the Earth at the equator. In the radiation belt, the main charge carriers are electrons. Their density is 2-3 orders of magnitude higher than the density of other charge carriers. And thus there is an electric current caused by the directed circular motion of the particles of the solar wind, carried away by the circular motion of the Earth, generating an electromagnetic “vortex” field.

It should be noted that the magnetic flux caused by the current of the solar wind also penetrates the flow of red-hot lava inside it, which rotates with the Earth. As a result of this interaction, an electromotive force is induced in it, under the action of which a current flows, which also creates a magnetic field. As a result, the Earth's magnetic field is the resulting field from the interaction of the ionospheric current and the lava current.

The actual picture of the Earth's magnetic field depends not only on the configuration of the current sheet, but also on the magnetic properties of the Earth's crust, as well as on the relative location of magnetic anomalies. Here we can draw an analogy with a circuit with current in the presence of a ferromagnetic core and without it. It is known that a ferromagnetic core not only changes the configuration of the magnetic field, but also significantly enhances it.

It is reliably established that the Earth's magnetic field reacts to solar activity, however, if we associate the occurrence of the magnetic field of planets only with current sheets in the liquid core interacting with the solar wind, then we can conclude that the planets of the solar system with the same direction of rotation must have the same direction magnetic fields. However, for example, Jupiter refutes this assertion.

Interestingly, when the solar wind interacts with the excited magnetic field of the Earth, the Earth is affected by a torque directed in the direction of the Earth's rotation. Thus, the Earth with respect to the solar wind behaves similarly to a DC motor with self-excitation. The source of energy (generator) in this case is the Sun. Since both the magnetic field and the torque acting on the earth depend on the current of the Sun, and the latter on the degree of solar activity, with an increase in solar activity, the torque acting on the Earth should increase and the speed of its rotation should increase.

Components of the geomagnetic field

The Earth's own magnetic field (geomagnetic field) can be divided into the following three main parts - the main (internal) magnetic field of the Earth, including world anomalies, magnetic fields of local regions of outer shells, alternating (external) magnetic field of the Earth.

1. MAIN MAGNETIC FIELD OF THE EARTH (internal) , which experiences slow changes in time (secular variations) with periods from 10 to 10,000 years, concentrated in the intervals of 10–20, 60–100, 600–1200 and 8000 years. The latter is associated with a change in the dipole magnetic moment by a factor of 1.5–2.

Magnetic lines of force created on a computer model of the geodynamo show how simpler the structure of the Earth's magnetic field is outside of it than inside the core (tangled tubes in the center). On the surface of the Earth, most of the magnetic field lines exit from the inside (long yellow tubes) at the South Pole and enter inward (long blue tubes) near the North.

Most people don't usually wonder why a compass needle points north or south. But the planet's magnetic poles weren't always aligned the way they are today.

Studies of minerals show that the Earth's magnetic field has changed its orientation from north to south and back hundreds of times over 4-5 billion years of the planet's existence. However, during the last 780 thousand years, nothing of the kind has happened, despite the fact that the average period of the change of magnetic poles is 250 thousand years. In addition, the geomagnetic field has weakened by almost 10% since it was first measured in the 1930s. 19th century (i.e., almost 20 times faster than if, having lost its source of energy, it would naturally reduce its strength). Is the next pole shift coming?

The source of magnetic field oscillations is hidden in the center of the Earth. Our planet, like other bodies of the solar system, creates its magnetic field with the help of an internal generator, the principle of which is the same as that of a conventional electric generator, which converts the kinetic energy of its moving particles into an electromagnetic field. In an electric generator, movement occurs in the turns of a coil, and inside a planet or a star - in a conductive liquid substance. A huge mass of molten iron with a volume 5 times the size of the Moon circulates in the core of the Earth, forming the so-called geodynamo.

Over the past ten years, scientists have developed new approaches to the study of the operation of the geodynamo and its magnetic properties. Satellites transmit clear snapshots of the geomagnetic field on the Earth's surface, and modern methods computer simulations and physical models created in laboratories help to interpret data from orbital observations. The experiments carried out prompted scientists to a new explanation of how the polarization reversal occurred in the past and how it can begin in the future.

In the internal structure of the Earth, a molten outer core is released, where complex turbulent convection generates a geomagnetic field.

Geodynamo Energy

What drives the geodynamo. By the 40s. of the last century, physicists recognized three necessary conditions for the formation of the planet's magnetic field, and subsequent scientific constructions proceeded from these provisions. The first condition is a large volume of electrically conductive liquid mass saturated with iron, which forms the outer core of the Earth. Below it is the inner core of the Earth, consisting of almost pure iron, and above it - 2900 km of solid rocks of the dense mantle and thin earth's crust, which form the continents and the ocean floor. The pressure on the core created by the earth's crust and mantle is 2 million times higher than on the surface of the earth. The temperature of the core is also extremely high - about 5000o Celsius, as is the temperature of the surface of the Sun.

The above parameters of the extreme environment predetermine the second requirement for the operation of the geodynamo: the need for an energy source to set the liquid mass in motion. Internal energy, partly of thermal, partly of chemical origin, creates conditions of expulsion inside the nucleus. The core heats up more at the bottom than at the top. (High temperatures have been “walled” inside it since the formation of the Earth.) This means that the hotter, less dense metal component of the core tends to rise. When the liquid mass reaches the upper layers, it loses some of its heat, giving it to the overlying mantle. The liquid iron then cools, becoming denser than the surrounding mass, and sinks. The process of moving heat by raising and lowering a liquid mass is called thermal convection.

The third necessary condition for maintaining a magnetic field is the rotation of the Earth. The resulting Coriolis force deflects the movement of the rising liquid mass inside the Earth in the same way as it turns ocean currents and tropical cyclones, whose eddies are visible on satellite images. At the center of the Earth, the Coriolis force twists the rising liquid mass into a corkscrew or spiral, like a broken spring.

The Earth has an iron-saturated liquid mass concentrated in its center, energy sufficient to maintain convection, and the Coriolis force that twists the convection currents. This factor is extremely important for maintaining the operation of the geodynamo for millions of years. But new knowledge is needed to answer the question of how the magnetic field is formed and why the poles change places from time to time.

Repolarization

Scientists have long wondered why the Earth's magnetic poles change places from time to time. Recent studies of the vortex movements of molten masses inside the Earth allow us to understand how polarization reversal occurs.

A magnetic field, much more intense and more complex than the field of the core, within which magnetic oscillations are formed, was found at the boundary between the mantle and the core. Electric currents arising in the core prevent direct measurements of its magnetic field.

It is important that most of the geomagnetic field is formed only in four vast areas at the boundary between the core and the mantle. Although the geodynamo produces a very strong magnetic field, only 1% of its energy propagates outside the core. The general configuration of the magnetic field measured at the surface is called a dipole, which most of the time is oriented along the earth's axis of rotation. As in the field of a linear magnet, the main geomagnetic flux is directed from the center of the Earth in the Southern Hemisphere and towards the center in the Northern Hemisphere. (The compass needle points to the geographic north pole, since the south magnetic pole of the dipole is nearby.) Space observations have shown that the magnetic flux has an uneven global distribution, the greatest intensity can be traced on the Antarctic coast, under North America and Siberia.

Ulrich R. Christensen of the Max Planck Solar System Research Institute in Katlenburg-Lindau, Germany, believes that these vast tracts of earth have existed for thousands of years and are maintained by an ever-evolving convection within the core. Could similar phenomena be the cause of the pole reversal? Historical geology testifies that the pole changes occurred in relatively short periods of time - from 4 thousand to 10 thousand years. If the geodynamo ceased its work, then the dipole would have existed for another 100 thousand years. A rapid reversal of polarity gives reason to believe that some unstable position violates the original polarity and causes a new change of poles.

In some cases, the mysterious instability can be explained by some chaotic change in the structure of the magnetic flux, which only accidentally leads to polarization reversal. However, the frequency of polarity reversal, which has become more and more stable over the past 120 million years, indicates the possibility of external regulation. One of the reasons for it may be a temperature drop in the lower layer of the mantle, and as a result, a change in the nature of the effusions of the core.

Some symptoms of polarization reversal were revealed in the analysis of maps that were made from the Magsat and Oersted satellites. Gauthier Hulot and his colleagues at the Geophysical Institute of Paris noted that long-term changes in the geomagnetic field occur at the core-mantle boundary in places where the direction of the geomagnetic flux is reversed from normal for a given hemisphere. The largest of the so-called sections of the reverse magnetic field stretches from the southern tip of Africa west to South America. In this area, the magnetic flux is directed inward, towards the core, while most of it in the Southern Hemisphere is directed from the center.

Areas where the magnetic field is directed in the opposite direction for a given hemisphere arise when twisted and winding lines of the magnetic field accidentally break through the Earth's core. Plots of a reverse magnetic field can significantly weaken the magnetic field on the Earth's surface, called a dipole, and indicate the beginning of a change in the earth's poles. They appear when a rising liquid mass pushes horizontal magnetic lines up in the molten outer core. Such a convective outpouring sometimes twists and squeezes out the magnetic line (a). At the same time, the forces of the Earth's rotation cause a helical circulation of the melt, which can tighten the loop on the extruded magnetic line (b). When the buoyant force is strong enough to throw the loop out of the core, a pair of magnetic flux patches forms at the core-mantle interface.

The most significant discovery made when comparing the latest measurements from Oersted and those made in 1980 was that new regions of reversed magnetic fields continue to form, for example, at the core-mantle interface under the east coast of North America and the Arctic. Moreover, the previously identified areas have grown and moved slightly towards the poles. At the end of the 80s. 20th century David Gubbins of the University of Leeds in England, studying old maps of the geomagnetic field, noted that the spread, growth and shift towards the poles of reversed magnetic fields explains the decrease in the strength of the dipole in historical time.

According to the theoretical provisions on power magnetic lines, arising in the liquid medium of the nucleus under the influence of the Coriolis force, small and large vortices twist the lines of force into a knot. Each turn collects more and more lines of force in the core, thus amplifying the energy of the magnetic field. If the process continues unhindered, then the magnetic field increases indefinitely. However, electrical resistance dissipates and aligns the turns of the field lines to such an extent as to stop the spontaneous growth of the magnetic field and continue the reproduction of internal energy.

Areas with intense magnetic normal and reverse fields form at the core-mantle boundary, where small and large eddies interact with east-west magnetic fields, described as toroidal, that penetrate the core. Turbulent fluid motions can twist toroidal field lines into loops, called poloidal fields, with a north-south orientation. Sometimes twisting occurs when a fluid mass rises. If such an outpouring is powerful enough, then the top of the poloidal loop is pushed out of the nucleus (see inset on the left). As a result of this expulsion, two sections are formed, where the loop crosses the core-mantle boundary. On one of them, the direction of the magnetic flux arises, coinciding with the general direction of the dipole field in the given hemisphere; in the other section, the flow is directed oppositely.

When the rotation brings the region of the reverse magnetic field closer to the geographic pole than the region with normal flux, there is a weakening of the dipole, which is most vulnerable near its poles. In this way, the reverse magnetic field in southern Africa can be explained. With a global onset of a reversal of the poles, sections of the reverse magnetic field can grow throughout the region near the geographic poles.

Contour maps of the Earth's magnetic field at the core-mantle boundary, compiled from satellite measurements, show that most of the magnetic flux is directed from the center of the Earth in the Southern Hemisphere and towards the center in the Northern Hemisphere. But in some areas, the picture is reversed. Reverse magnetic fields grew in number and size between 1980 and 2000. If they fill the entire space at both poles, then a polarization reversal can occur.

Pole reversal models

The magnetic field maps show how, with normal polarity, most of the magnetic flux is directed from the center of the Earth ( yellow) in the Southern Hemisphere and towards its center (light blue) in the Northern Hemisphere (a). The beginning of polarization reversal is marked by the appearance of several areas of the reversed magnetic field (blue in the Southern Hemisphere and yellow in the Northern Hemisphere), reminiscent of the formation of its sections at the core-mantle boundary. For about 3 thousand years, they reduced the strength of the dipole field, which was replaced by a weaker, but more complex transitional field at the core-mantle boundary (b). The change of poles became a frequent phenomenon after 6 thousand years, when sections of the reverse magnetic field began to prevail at the core-mantle boundary (c). By this time, a complete reversal of poles had also manifested itself on the surface of the Earth. But only after another 3 thousand years there was a complete replacement of the dipole, including the core of the Earth (d).

What happens to the internal magnetic field today?

Most of us know that the geographic poles are constantly making complex looping movements in the direction daily rotation Earth (precession of the axis with a period of 25776 years). Typically, these movements occur near the imaginary axis of rotation of the Earth and do not lead to noticeable climate change. Read more about pole shift. But few people noticed that at the end of 1998 the overall component of these movements shifted. Within a month, the pole shifted towards Canada by 50 kilometers. At present, the north pole is “creeping” along the 120th parallel of the western longitude. It can be assumed that if the current trend in the movement of the poles continues until 2010, then the north pole can move 3-4 thousand kilometers. The end point of the drift is the Great Bear Lakes in Canada. South Pole, respectively, will shift from the center of Antarctica to the Indian Ocean.

The shift of the magnetic poles has been recorded since 1885. Over the past 100 years, the magnetic pole in the southern hemisphere has moved almost 900 km and Indian Ocean. The latest data on the state of the Arctic magnetic pole (moving towards the East Siberian world magnetic anomaly through the Arctic Ocean): showed that from 1973 to 1984 its run was 120 km, from 1984 to 1994. - more than 150 km. It is characteristic that these data are calculated, but they were confirmed by specific measurements of the north magnetic pole. According to the data at the beginning of 2002, the drift velocity of the north magnetic pole increased from 10 km / year in the 70s to 40 km / year in 2001 year.

In addition, the strength of the earth's magnetic field is decreasing, and very unevenly. Thus, over the past 22 years, it has decreased by an average of 1.7 percent, and in some regions - for example, in the South Atlantic Ocean - by 10 percent. However, in some places on our planet, the magnetic field strength, contrary to the general trend, even increased slightly.

We emphasize that the acceleration of the movement of the poles (by an average of 3 km/year per decade) and their movement along the corridors of magnetic pole reversal (more than 400 paleoinversions made it possible to identify these corridors) makes us suspect that this movement of the poles should not be seen as an excursion, and the polarity reversal of the Earth's magnetic field.

Acceleration can bring the movement of the poles up to 200 km per year, so that the reversal will be carried out much faster than is expected by researchers who are far from professional estimates of the real processes of polarity reversal.

In the history of the Earth, changes in the position of the geographic poles have occurred repeatedly, and this phenomenon is primarily associated with the glaciation of vast areas of land and cardinal changes in the climate of the entire planet. But echoes in human history received only last disaster, most likely associated with a pole shift that occurred about 12 thousand years ago. We all know that Mammoths are extinct. But everything was much more serious.

The extinction of hundreds of animal species is undeniable. There are discussions about the Flood and the Destruction of Atlantis. But one thing is certain - the echoes of the greatest catastrophe in the memory of mankind have a real basis. And it is caused, most likely, by a pole shift of only 2000 km.

The model below shows the magnetic field inside the nucleus (a bunch of field lines in the center) and the appearance of a dipole (long curved lines) 500 years (a) before the middle of the repolarization (b) of the magnetic dipole and 500 years later at the stage of its completion (c).

The magnetic field of the Earth's geological past

Over the past 150 million years, polarization reversal has occurred hundreds of times, as evidenced by minerals magnetized by the Earth's field during the heating of rocks. Then the rocks cooled down, and the minerals retained their former magnetic orientation.

Scales of magnetic field reversals: I – for the last 5 million years; II - for the last 55 million years. Black color - normal magnetization, white color - reverse magnetization (according to W.W. Harland et al., 1985)

Magnetic field reversals are a change in the sign of the axes of a symmetrical dipole. In 1906, B. Brun, measuring the magnetic properties of relatively young Neogene lavas in central France, found that their magnetization is opposite in direction to the modern geomagnetic field, that is, the North and South magnetic poles, as it were, changed places. The presence of reversely magnetized rocks is not a consequence of some unusual conditions at the time of its formation, but the result of the inversion of the Earth's magnetic field at the moment. The polarity reversal of the geomagnetic field is the most important discovery in paleomagnetology, which made it possible to create new science magnetostratigraphy, which studies the division of rock deposits on the basis of their direct or reversed magnetization. And the main thing here is to prove the synchronism of these sign conversions within the entire globe. In this case, a very effective method of correlation of deposits and events is in the hands of geologists.

In the real magnetic field of the Earth, the time during which the sign of the polarity changes can be either short, up to a thousand years, or even millions of years.
Time intervals of the predominance of any one polarity are called geomagnetic epochs, and some of them are named after the outstanding geomagnetologists Brunness, Matuyama, Gauss and Gilbert. Within the epochs, shorter intervals of one polarity or another are distinguished, called geomagnetic episodes. The most effective identification of intervals of direct and reverse polarity of the geomagnetic field was carried out for geologically young lava flows in Iceland, Ethiopia and other places. The disadvantage of these studies is that the process of lava outpouring was an intermittent process, so it is quite possible to miss any magnetic episode.

When the opportunity arose for selected breeds of the same age, but taken on different continents, to determine the position of the paleomagnetic poles of the time interval of interest to us, it turned out that the calculated averaged pole, say, for the Upper Jurassic rocks (170 - 144 million years) of North America and the same pole for the same rocks of Europe will be located in different places. It turned out, as it were, two North Poles, which cannot be with a dipole system. In order for the North Pole to be one, it was necessary to change the position of the continents on the surface of the Earth. In our case, this meant the convergence of Europe and North America until their shelf edges coincide, that is, to an ocean depth of about 200 m. In other words, it is not the poles that move, but the continents.

The use of the paleomagnetic method made it possible to carry out detailed reconstructions of the opening of the relatively young Atlantic, Indian, and Arctic oceans and to understand the history of the development of the older Pacific Ocean. The current arrangement of the continents is the result of the breakup of the supercontinent Pangea, which began about 200 million years ago. The linear magnetic field of the oceans makes it possible to determine the speed of plate movement, and its pattern provides the best information for geodynamic analysis.

Thanks to paleomagnetic studies, it was established that the split of Africa and Antarctica occurred 160 million years ago. The most ancient anomalies with an age of 170 million years (Middle Jurassic) were found along the edges of the Atlantic near the coasts of North America and Africa. This is the time of the beginning of the disintegration of the supercontinent. The South Atlantic arose 120 - 110 million years ago, and the North much later (80 - 65 million years ago), etc. Similar examples one can cite any of the oceans and, as if “reading” the paleomagnetic record, reconstruct the history of their development and the movement of lithospheric plates.

World anomalies– deviations from the equivalent dipole up to 20% of the intensity of individual regions with characteristic dimensions up to 10,000 km. These anomalous fields experience secular variations leading to changes over time over many years and centuries. Examples of anomalies: Brazilian, Canadian, Siberian, Kursk. In the course of secular variations, world anomalies shift, disintegrate and reappear. At low latitudes, there is a westerly drift in longitude at a rate of 0.2° per year.

2. MAGNETIC FIELDS OF LOCAL REGIONS outer shells with a length of several to hundreds of kilometers. They are due to the magnetization of rocks in the upper layer of the Earth, which make up the earth's crust and are located close to the surface. One of the most powerful is the Kursk magnetic anomaly.

3. EARTH'S VARIABLE MAGNETIC FIELD (also called external) is determined by sources in the form of current systems located outside the earth's surface and in its atmosphere. The main sources of such fields and their changes are corpuscular flows of magnetized plasma coming from the Sun together with the solar wind and forming the structure and shape of the Earth's magnetosphere.

First of all, it can be seen that this structure has a "layered" form. However, sometimes one can observe a "break" of the upper layers, apparently occurring under the influence of an increase in the solar wind. For example like here:

At the same time, the degree of “heating” depends on the speed and density of the Solar wind at such a moment, it is reflected in the color range from yellow to purple, which actually reflects the pressure on the magnetic field in this zone (upper right figure).

The structure of the magnetic field of the earth's atmosphere (external magnetic field of the Earth)

The earth's magnetic field is influenced by the flow of magnetized solar plasma. As a result of interaction with the Earth's field, the outer boundary of the near-Earth magnetic field is formed, called magnetopause. It limits the earth's magnetosphere. Due to the influence of solar corpuscular flows, the size and shape of the magnetosphere are constantly changing, and an alternating magnetic field arises, determined by external sources. Its variability owes its origin to the current systems developing at different heights from the lower layers of the ionosphere to the magnetopause. Changes in the Earth's magnetic field over time, caused by various reasons, are called geomagnetic variations, which differ both in their duration and localization on the Earth and in its atmosphere.

The magnetosphere is a region of near-Earth space controlled by the Earth's magnetic field. The magnetosphere is formed as a result of the interaction of the solar wind with the plasma of the upper atmosphere and the Earth's magnetic field. The shape of the magnetosphere is a cavity and a long tail, which repeat the shape of magnetic field lines. The subsolar point is on average at a distance of 10 Earth radii, and the magnetotail extends beyond the orbit of the Moon. The topology of the magnetosphere is determined by the regions of intrusion of the solar plasma into the magnetosphere and by the character of the current systems.

The tail of the magnetosphere is formed by the lines of force of the Earth's magnetic field, emerging from the polar regions and elongated under the action of the solar wind for hundreds of Earth radii from the Sun to the night side of the Earth. As a result, the plasma of the solar wind and solar corpuscular streams, as it were, flow around the Earth's magnetosphere, giving it a peculiar tailed shape.
In the magnetotail, at large distances from the Earth, the intensity of the Earth's magnetic field, and hence their protective properties, are weakened, and some particles of the solar plasma are able to penetrate and get into the Earth's magnetosphere and magnetic traps of the radiation belts. Penetrating into the head part of the magnetosphere into the area of ​​aurora ovals under the influence of the changing pressure of the solar wind and the interplanetary field, the tail serves as a place for the formation of streams of precipitating particles that cause auroras and auroral currents. The magnetosphere is separated from interplanetary space by the magnetopause. Along the magnetopause, particles of corpuscular streams flow around the magnetosphere. The influence of the solar wind on the earth's magnetic field is sometimes very strong. The magnetopause is the outer boundary of the Earth's (or planet's) magnetosphere, on which the dynamic pressure of the solar wind is balanced by the pressure of its own magnetic field. With typical solar wind parameters, the subsolar point is 9–11 Earth radii away from the center of the Earth. During the period of magnetic disturbances on Earth, the magnetopause can go beyond geostationary orbit(6.6 Earth radii). When the solar wind is weak, the subsolar point is at a distance of 15–20 Earth radii.

Geomagnetic variations

Changes in the Earth's magnetic field over time under the influence of various factors are called geomagnetic variations. The difference between the observed value of the magnetic field strength and its average value over any long period of time, for example, a month or a year, is called geomagnetic variation. According to observations, geomagnetic variations change continuously in time, and such changes are often periodic.

daily variations Geomagnetic fields occur regularly, mainly due to currents in the Earth's ionosphere caused by changes in the illumination of the Earth's ionosphere by the Sun during the day.

Daily geomagnetic variation for the period 19.03.2010 12:00 to 21.03.2010 00:00

The Earth's magnetic field is described by seven parameters. To measure the earth's magnetic field at any point, we must measure the direction and strength of the field. Parameters describing the direction of the magnetic field: declination (D), inclination (I). D and I are measured in degrees. The strength of the general field (F) is described by the horizontal component (H), the vertical component (Z), and the northern (X) and eastern (Y) components of the horizontal strength. These components can be measured in oersteds (1 oersted = 1 gauss), but usually in nanoteslas (1nT x 100,000 = 1 oersted).

irregular variations magnetic fields arise due to the impact of the solar plasma flow (solar wind) on the Earth's magnetosphere, as well as changes within the magnetosphere and the interaction of the magnetosphere with the ionosphere.

The figure below shows (from left to right) images of the current - magnetic field, pressure, convection currents in the ionosphere, as well as graphs of changes in the speed and density of the solar wind (V, Dens) and the values ​​of the vertical and eastern components of the Earth's external magnetic field.

27 day variations exist as a tendency to repeat the increase in geomagnetic activity every 27 days, corresponding to the period of rotation of the Sun relative to the earthly observer. This pattern is associated with the existence of long-lived active regions on the Sun, observed during several rotations of the Sun. This pattern manifests itself in the form of a 27-day recurrence of magnetic activity and magnetic storms.

Seasonal variations of magnetic activity are confidently detected on the basis of monthly average data on magnetic activity obtained by processing observations over several years. Their amplitude increases with the growth of the total magnetic activity. It is found that the seasonal variations of magnetic activity have two maxima, corresponding to the periods of equinoxes, and two minima, corresponding to the periods of solstices. The reason for these variations is the formation of active regions on the Sun, which are grouped in zones from 10 to 30° of northern and southern heliographic latitudes. Therefore, during the periods of equinoxes, when the planes of the earth's and solar equators coincide, the Earth is most exposed to the action of active regions on the Sun.

11 year variations. The relationship between solar activity and magnetic activity manifests itself most clearly when comparing long series of observations that are multiples of 11 summer periods solar activity. The best known measure of solar activity is the number of sunspots. It was found that during the years of the maximum number of sunspots, the magnetic activity also reaches its maximum value, however, the increase in magnetic activity lags somewhat in relation to the growth of the solar one, so that, on average, this delay is one year.

Age Variations - slow variations of the elements of terrestrial magnetism with periods of several years or more. Unlike diurnal, seasonal, and other variations of external origin, secular variations are associated with sources lying inside the earth's core. The amplitude of secular variations reaches tens of nT/year; changes in the average annual values ​​of such elements are called the secular variation. The isolines of secular variations are concentrated around several points - the centers or foci of the secular variation, in these centers the magnitude of the secular variation reaches its maximum values.

Magnetic storm - impact on the human body

The local characteristics of the magnetic field change and fluctuate sometimes for many hours, and then are restored to the previous level. This phenomenon is called a magnetic storm. Magnetic storms often start suddenly and all over the globe at the same time.

A shock wave of the solar wind reaches the Earth's orbit a day after the solar flare and a magnetic storm begins. Seriously ill patients clearly react from the first hours after the outbreak on the Sun, the rest - from the moment the storm began on Earth. Common to all is the change in biorhythms during these hours. The number of cases of myocardial infarction increases the next day after the outbreak (about 2 times more compared to magnetically quiet days). On the same day, a magnetospheric storm caused by a flare begins. In absolutely healthy people, the immune system is activated, there may be an increase in working capacity, an improvement in mood.

Note: geomagnetic calm, lasting several days or more in a row, acts on the body of a city dweller, in many ways, like a storm - depressingly, causing depression and weakening of the immune system. A slight "bounce" of the magnetic field within Kp = 0 - 3 helps to more easily endure changes in atmospheric pressure and other meteorological factors.

The following gradation of Kp-index values ​​was adopted:

Kp = 0-1 - geomagnetic situation is calm (calm);

Kp = 1-2 - geomagnetic environment from calm to slightly disturbed;

Kp = 3-4 - from slightly perturbed to perturbed;

Kp = 5 and above – weak magnetic storm (level G1);

Kp = 6 and above – average magnetic storm (level G2);

Kp = 7 and above – strong magnetic storm (level G3); accidents are possible, deterioration of health in weather-dependent people

Kp = 8 and above – very strong magnetic storm (level G4);

Kp = 9 – extremely strong magnetic storm (G5 level) – the maximum possible value.

Online monitoring of the state of the magnetosphere and magnetic storms here:

As a result of numerous studies carried out at the Institute space research(IKI), Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation (IZMIRAN), Medical Academy. THEM. Sechenov and the Institute of Medical and Biological Problems of the Russian Academy of Sciences, it turned out that during geomagnetic storms in patients with pathology of the cardiovascular system, especially in those who had myocardial infarction, blood pressure jumped, blood viscosity increased markedly, its flow rate in capillaries slowed down, and vascular tone changed. and stress hormones are activated.

In the body of some healthy people, changes also occurred, but they mainly caused fatigue, weakening of attention, headaches, dizziness and did not pose a serious danger. The body of the cosmonauts reacted somewhat more strongly to the changes: they developed arrhythmias and changed vascular tone. Experiments in orbit also showed that it is electromagnetic fields that negatively affect the human condition, and not other factors that act on Earth, but are excluded in space. In addition, another “risk group” was identified – healthy people with an overstressed adaptive system associated with exposure to additional stress (in this case, weightlessness, which also affects the cardiovascular system).

The researchers came to the conclusion that geomagnetic storms cause the same adaptive stress as a sharp change in time zones, knocking down the biological daily rhythms of a person. Sudden flares on the Sun and other manifestations of solar activity dramatically change the relatively regular rhythms of the Earth's geomagnetic field, which causes animals and humans to malfunction in their own rhythms and generates adaptive stress.

Healthy people cope with it relatively easily, but for people with pathology of the cardiovascular system, with an overstrained adaptive system, and for newborns, it is potentially dangerous.

It is impossible to predict the response. It all depends on many factors: on the human condition, on the nature of the storm, on the frequency spectrum electromagnetic oscillations etc. It is still unknown how changes in the geomagnetic field affect the biochemical and biophysical processes occurring in the body: what are the receivers of geomagnetic signals-receptors, whether a person reacts to electromagnetic radiation with the whole body, individual organs or even individual cells. At present, in order to study the influence of solar activity on people, a laboratory of heliobiology is being opened at the Institute of Space Research.

9. N.V. Koronovsky. THE MAGNETIC FIELD OF THE GEOLOGICAL PAST OF THE EARTH // Lomonosov Moscow State University. M.V. Lomonosov. Soros Educational Journal, N5, 1996, p. 56-63

According to modern concepts, it was formed about 4.5 billion years ago, and from that moment our planet is surrounded by a magnetic field. Everything on Earth, including people, animals and plants, is affected by it.

The magnetic field extends up to a height of about 100,000 km (Fig. 1). It deflects or captures solar wind particles that are harmful to all living organisms. These charged particles form the Earth's radiation belt, and the entire region of near-Earth space in which they are located is called magnetosphere(Fig. 2). On the side of the Earth illuminated by the Sun, the magnetosphere is bounded by a spherical surface with a radius of approximately 10-15 Earth radii, and on the opposite side it is elongated like a cometary tail over a distance of up to several thousand Earth radii, forming a geomagnetic tail. The magnetosphere is separated from the interplanetary field by a transition region.

Earth's magnetic poles

The axis of the earth's magnet is inclined with respect to the axis of rotation of the earth by 12°. It is located about 400 km away from the center of the Earth. The points at which this axis intersects the surface of the planet are magnetic poles. The magnetic poles of the Earth do not coincide with the true geographic poles. At present, the coordinates of the magnetic poles are as follows: north - 77 ° N.L. and 102° W; southern - (65 ° S and 139 ° E).

Rice. 1. The structure of the Earth's magnetic field

Rice. 2. Structure of the magnetosphere

The lines of force that run from one magnetic pole to the other are called magnetic meridians. An angle is formed between the magnetic and geographic meridians, called magnetic declination. Every place on Earth has its own angle of declination. In the Moscow region, the declination angle is 7° to the east, and in Yakutsk, about 17° to the west. This means that the northern end of the compass needle in Moscow deviates by T to the right of the geographic meridian passing through Moscow, and in Yakutsk - by 17 ° to the left of the corresponding meridian.

A freely suspended magnetic needle is located horizontally only on the line of the magnetic equator, which does not coincide with the geographic one. If you move north of the magnetic equator, then the northern end of the arrow will gradually drop. The angle formed by a magnetic needle and a horizontal plane is called magnetic inclination. At the North and South magnetic poles, the magnetic inclination is greatest. It is equal to 90°. At the North Magnetic Pole, a freely suspended magnetic needle will be installed vertically with the north end down, and at the South Magnetic Pole, its south end will go down. Thus, the magnetic needle shows the direction of the magnetic field lines above the earth's surface.

Over time, the position of the magnetic poles relative to the earth's surface changes.

The magnetic pole was discovered by explorer James C. Ross in 1831, hundreds of kilometers from its current location. On average, he moves 15 km per year. AT last years the speed of movement of the magnetic poles has increased dramatically. For example, the North Magnetic Pole is currently moving at a speed of about 40 km per year.

The reversal of the Earth's magnetic poles is called magnetic field inversion.

Throughout the geological history of our planet, the earth's magnetic field has changed its polarity more than 100 times.

The magnetic field is characterized by intensity. In some places on the Earth, magnetic field lines deviate from the normal field, forming anomalies. For example, in the region of the Kursk Magnetic Anomaly (KMA), the field strength is four times higher than normal.

There are diurnal changes in the Earth's magnetic field. The reason for these changes in the Earth's magnetic field is the electric currents flowing in the atmosphere for high altitude. They are caused by solar radiation. Under the action of the solar wind, the Earth's magnetic field is distorted and acquires a "tail" in the direction from the Sun, which extends for hundreds of thousands of kilometers. The main reason for the emergence of the solar wind, as we already know, is the grandiose ejections of matter from the corona of the Sun. When moving towards the Earth, they turn into magnetic clouds and lead to strong, sometimes extreme disturbances on the Earth. Especially strong perturbations of the Earth's magnetic field - magnetic storms. Some magnetic storms begin unexpectedly and almost simultaneously throughout the Earth, while others develop gradually. They can last for hours or even days. Often, magnetic storms occur 1-2 days after a solar flare due to the passage of the Earth through a stream of particles ejected by the Sun. Based on the delay time, the speed of such a corpuscular flow is estimated at several million km/h.

During strong magnetic storms, the normal operation of the telegraph, telephone and radio is disrupted.

Magnetic storms are often observed at a latitude of 66-67° (in the aurora zone) and occur simultaneously with the auroras.

The structure of the Earth's magnetic field varies depending on the latitude of the area. The permeability of the magnetic field increases towards the poles. Above the polar regions, the magnetic field lines are more or less perpendicular to the earth's surface and have a funnel-shaped configuration. Through them, part of the solar wind from the day side penetrates into the magnetosphere, and then into the upper atmosphere. Particles from the tail of the magnetosphere rush here during magnetic storms, reaching the boundaries upper atmosphere at high latitudes in the northern and southern hemispheres. It is these charged particles that cause the auroras here.

So, magnetic storms and daily changes in the magnetic field are explained, as we have already found out, by solar radiation. But what is the main reason that creates the permanent magnetism of the Earth? Theoretically, it was possible to prove that 99% of the Earth's magnetic field is caused by sources hidden inside the planet. The main magnetic field is due to sources located in the depths of the Earth. They can be roughly divided into two groups. Most of them are associated with processes in the earth's core, where, as a result of continuous and regular movements of the electrically conductive substance, a system of electric currents is created. The other is connected with the fact that the rocks of the earth's crust, being magnetized by the main electric field(field of the nucleus), create their own magnetic field, which is added to the magnetic field of the nucleus.

In addition to the magnetic field around the Earth, there are other fields: a) gravitational; b) electrical; c) thermal.

Gravity field The earth is called the gravity field. It is directed along a plumb line perpendicular to the surface of the geoid. If the Earth had an ellipsoid of revolution and the masses were evenly distributed in it, then it would have a normal gravitational field. The difference between the intensity of the real gravitational field and the theoretical one is the anomaly of gravity. Different material composition, density of rocks cause these anomalies. But other reasons are also possible. They can be explained by the following process - the balance of the solid and relatively light earth's crust on the heavier upper mantle, where the pressure of the overlying layers is equalized. These currents cause tectonic deformations, the movement of lithospheric plates and thereby create the Earth's macrorelief. Gravity keeps the atmosphere, hydrosphere, people, animals on Earth. The force of gravity must be taken into account when studying processes in a geographic envelope. The term " geotropism” called the growth movements of plant organs, which, under the influence of the force of gravity, always provide a vertical direction of growth of the primary root perpendicular to the surface of the Earth. Gravitational biology uses plants as experimental objects.

If gravity is not taken into account, it is impossible to calculate the initial data for launching rockets and spaceships, make gravimetric exploration of ore minerals and, finally, the further development of astronomy, physics and other sciences is impossible.

The content of the article

THE MAGNETIC FIELD OF THE EARTH. Most of the planets in the solar system have magnetic fields to some extent. In decreasing dipole magnetic moment, Jupiter and Saturn are in the first place, followed by the Earth, Mercury and Mars, and in relation to the Earth's magnetic moment, the value of their moments is 20,000, 500, 1, 3/5000 3/10000. The dipole magnetic moment of the Earth in 1970 was 7.98·10 25 G/cm 3 (or 8.3·10 22 A.m 2), decreasing over the decade by 0.04·10 25 G/cm 3 . The average field strength on the surface is about 0.5 Oe (5 10 -5 T). The shape of the main magnetic field of the Earth to distances less than three radii is close to the field of an equivalent magnetic dipole. Its center is displaced relative to the center of the Earth in the direction of 18° N. latitude. and 147.8° E. e. The axis of this dipole is inclined to the axis of rotation of the Earth by 11.5°. At the same angle, the geomagnetic poles are separated from the corresponding geographic poles. At the same time, the south geomagnetic pole is located in the northern hemisphere. It is currently located near the northern geographic pole Lands in North Greenland. Its coordinates are j = 78.6 + 0.04° T NL, l = 70.1 + 0.07° T W, where T is the number of decades since 1970. At the north magnetic pole, j = 75° S, l = 120.4°E (in Antarctica). The real magnetic field lines of the Earth's magnetic field are on average close to the lines of force of this dipole, differing from them in local irregularities associated with the presence of magnetized rocks in the crust. As a result of secular variations, the geomagnetic pole precesses relative to the geographic pole with a period of about 1200 years. At large distances, the Earth's magnetic field is asymmetric. Under the influence of the plasma flow (solar wind) emanating from the Sun, the Earth's magnetic field is distorted and acquires a "tail" in the direction from the Sun, which extends for hundreds of thousands of kilometers, going beyond the orbit of the Moon.

A special section of geophysics that studies the origin and nature of the Earth's magnetic field is called geomagnetism. Geomagnetism considers the problems of the emergence and evolution of the main, constant component geomagnetic field, the nature of the variable component (about 1% of the main field), as well as the structure of the magnetosphere - the uppermost magnetized plasma layers of the earth's atmosphere interacting with the solar wind and protecting the Earth from cosmic penetrating radiation. An important task is to study the patterns of geomagnetic field variations, since they are caused by external influences associated primarily with solar activity. .

Origin of the magnetic field.

The observed properties of the Earth's magnetic field are consistent with the concept of its origin due to the hydromagnetic dynamo mechanism. In this process, the initial magnetic field is strengthened as a result of movements (usually convective or turbulent) of electrically conductive matter in the liquid core of the planet or in the plasma of the star. At a temperature of a substance of several thousand K, its conductivity is high enough so that convective movements occurring even in a weakly magnetized medium can excite changing electric currents that, in accordance with the laws of electromagnetic induction, can create new magnetic fields. The damping of these fields either creates thermal energy (according to Joule's law) or leads to the emergence of new magnetic fields. Depending on the nature of the motions, these fields can either weaken or strengthen the original fields. To strengthen the field, a certain asymmetry of movements is sufficient. Thus, a necessary condition for a hydromagnetic dynamo is the very presence of motions in a conducting medium, and a sufficient condition is the presence of a certain asymmetry (helicity) of the internal flows of the medium. When these conditions are met, the amplification process continues until the Joule heat losses, which increase with increasing current strength, balance the influx of energy due to hydrodynamic movements.

Dynamo effect - self-excitation and maintenance of magnetic fields in a stationary state due to the movement of a conductive liquid or gas plasma. Its mechanism is similar to the generation of electric current and magnetic field in a self-excited dynamo. The dynamo effect is associated with the origin of the own magnetic fields of the Sun of the Earth and planets, as well as their local fields, for example, the fields of spots and active regions.

Components of the geomagnetic field.

The Earth's own magnetic field (geomagnetic field) can be divided into the following three main parts.

1. The main magnetic field of the Earth, experiencing slow changes in time (secular variations) with periods from 10 to 10,000 years, concentrated in the intervals of 10–20, 60–100, 600–1200 and 8000 years. The latter is associated with a change in the dipole magnetic moment by a factor of 1.5–2.

2. World anomalies - deviations from the equivalent dipole up to 20% of the intensity of individual areas with characteristic sizes up to 10,000 km. These anomalous fields experience secular variations leading to changes over time over many years and centuries. Examples of anomalies: Brazilian, Canadian, Siberian, Kursk. In the course of secular variations, world anomalies shift, disintegrate and reappear. At low latitudes, there is a westerly drift in longitude at a rate of 0.2° per year.

3. Magnetic fields of local regions of outer shells with a length from several to hundreds of kilometers. They are due to the magnetization of rocks in the upper layer of the Earth, which make up the earth's crust and are located close to the surface. One of the most powerful is the Kursk magnetic anomaly.

4. The alternating magnetic field of the Earth (also called external) is determined by sources in the form of current systems located outside the earth's surface and in its atmosphere. The main sources of such fields and their changes are corpuscular flows of magnetized plasma coming from the Sun together with the solar wind and forming the structure and shape of the Earth's magnetosphere.

The structure of the magnetic field of the earth's atmosphere.

The earth's magnetic field is influenced by the flow of magnetized solar plasma. As a result of interaction with the Earth's field, the outer boundary of the near-Earth magnetic field is formed, called the magnetopause. It limits the earth's magnetosphere. Due to the impact of solar corpuscular flows, the size and shape of the magnetosphere are constantly changing, and an alternating magnetic field arises, determined by external sources. Its variability owes its origin to the current systems developing at different heights from the lower layers of the ionosphere to the magnetopause. Changes in the Earth's magnetic field over time, caused by various reasons, are called geomagnetic variations, which differ both in their duration and localization on the Earth and in its atmosphere.

The magnetosphere is a region of near-Earth space controlled by the Earth's magnetic field. The magnetosphere is formed as a result of the interaction of the solar wind with the plasma of the upper atmosphere and the Earth's magnetic field. The shape of the magnetosphere is a cavity and a long tail, which repeat the shape of magnetic field lines. The subsolar point is on average at a distance of 10 Earth radii, and the magnetotail extends beyond the orbit of the Moon. The topology of the magnetosphere is determined by the regions of intrusion of the solar plasma into the magnetosphere and by the character of the current systems.

The tail of the magnetosphere is formed the lines of force of the Earth's magnetic field, emerging from the polar regions and elongated under the action of the solar wind for hundreds of Earth radii from the Sun to the night side of the Earth. As a result, the plasma of the solar wind and solar corpuscular streams, as it were, flow around the Earth's magnetosphere, giving it a peculiar tailed shape. In the magnetotail, at large distances from the Earth, the intensity of the Earth's magnetic field, and hence their protective properties, are weakened, and some particles of the solar plasma are able to penetrate and get into the Earth's magnetosphere and magnetic traps of the radiation belts. Penetrating into the head part of the magnetosphere into the region of aurora ovals under the influence of the changing pressure of the solar wind and the interplanetary field, the tail serves as a place for the formation of streams of precipitating particles that cause auroras and auroral currents. The magnetosphere is separated from interplanetary space by the magnetopause. Along the magnetopause, particles of corpuscular streams flow around the magnetosphere. The influence of the solar wind on the earth's magnetic field is sometimes very strong. magnetopause – the outer boundary of the Earth's (or planet's) magnetosphere, on which the dynamic pressure of the solar wind is balanced by the pressure of its own magnetic field. With typical solar wind parameters, the subsolar point is 9–11 Earth radii away from the center of the Earth. During the period of magnetic disturbances on the Earth, the magnetopause can go beyond the geostationary orbit (6.6 Earth radii). When the solar wind is weak, the subsolar point is at a distance of 15–20 Earth radii.

Sunny wind -

outflow of solar corona plasma into interplanetary space. At the level of the Earth's orbit average speed particles of the solar wind (protons and electrons) are about 400 km/s, the number of particles is several tens per 1 cm 3 .

Magnetic storm.

The local characteristics of the magnetic field change and fluctuate sometimes for many hours, and then are restored to the previous level. This phenomenon is called magnetic storm. Magnetic storms often start suddenly and all over the globe at the same time.

geomagnetic variations.

Changes in the Earth's magnetic field over time under the influence of various factors are called geomagnetic variations. The difference between the observed value of the magnetic field strength and its average value over any long period of time, for example, a month or a year, is called geomagnetic variation. According to observations, geomagnetic variations change continuously in time, and such changes are often periodic.

daily variations. Daily variations in the geomagnetic field occur regularly, mainly due to currents in the Earth's ionosphere caused by changes in the illumination of the Earth's ionosphere by the Sun during the day.

irregular variations. Irregular variations in the magnetic field arise due to the influence of the solar plasma flow (solar wind) on the Earth's magnetosphere, as well as changes within the magnetosphere and the interaction of the magnetosphere with the ionosphere.

27 day variations. 27-day variations exist as a tendency to repeat the increase in geomagnetic activity every 27 days, corresponding to the period of rotation of the Sun relative to the Earth observer. This pattern is associated with the existence of long-lived active regions on the Sun, observed during several rotations of the Sun. This pattern manifests itself in the form of a 27-day recurrence of magnetic activity and magnetic storms.

Seasonal variations. Seasonal variations in magnetic activity are confidently revealed on the basis of monthly average data on magnetic activity obtained by processing observations over several years. Their amplitude increases with the growth of the total magnetic activity. It is found that the seasonal variations of magnetic activity have two maxima, corresponding to the periods of equinoxes, and two minima, corresponding to the periods of solstices. The reason for these variations is the formation of active regions on the Sun, which are grouped in zones from 10 to 30° of northern and southern heliographic latitudes. Therefore, during the periods of equinoxes, when the planes of the earth's and solar equators coincide, the Earth is most exposed to the action of active regions on the Sun.

11 year variations. The connection between solar activity and magnetic activity manifests itself most clearly when comparing long series of observations that are multiples of 11 year periods of solar activity. The best known measure of solar activity is the number of sunspots. It was found that during the years of the maximum number of sunspots, the magnetic activity also reaches its maximum value, however, the increase in magnetic activity lags somewhat in relation to the growth of the solar one, so that, on average, this delay is one year.

Age Variations- slow variations of the elements of terrestrial magnetism with periods of several years or more. Unlike diurnal, seasonal, and other variations of external origin, secular variations are associated with sources lying inside the earth's core. The amplitude of secular variations reaches tens of nT/year; changes in the average annual values ​​of such elements are called the secular variation. The isolines of secular variations are concentrated around several points - the centers or foci of the secular variation, in these centers the magnitude of the secular variation reaches its maximum values.

Radiation belts and cosmic rays.

The radiation belts of the Earth are two regions of the nearest near-Earth space, which surround the Earth in the form of closed magnetic traps.

They contain huge streams of protons and electrons captured by the dipole magnetic field of the Earth. The Earth's magnetic field has a strong influence on electrically charged particles moving in the near-Earth outer space. There are two main sources of these particles: cosmic rays, i.e. energetic (from 1 to 12 GeV) electrons, protons and nuclei of heavy elements, arriving at almost light speeds, mainly from other parts of the Galaxy. And corpuscular streams of less energetic charged particles (10 5 -10 6 eV) ejected by the Sun. In a magnetic field, electrical particles move in a spiral; the trajectory of the particle, as it were, winds around the cylinder, along the axis of which passes field line. The radius of this imaginary cylinder depends on the field strength and particle energy. The greater the energy of the particle, the larger the radius (it is called the Larmor radius) for a given field strength. If the Larmor radius is much smaller than the radius of the Earth, the particle does not reach its surface, but is captured by the Earth's magnetic field. If the Larmor radius is much greater than the radius of the Earth, the particle moves as if there were no magnetic field, the particles penetrate the Earth's magnetic field in the equatorial regions if their energy is greater than 10 9 eV. Such particles invade the atmosphere and, upon collision with its atoms, cause nuclear transformations, which produce certain amounts of secondary cosmic rays. These secondary cosmic rays are already being registered on the Earth's surface. To study cosmic rays in their original form (primary cosmic rays), equipment is raised on rockets and artificial earth satellites. Approximately 99% of the energetic particles that "pierce" the Earth's magnetic screen are cosmic rays of galactic origin, and only about 1% is formed on the Sun. The Earth's magnetic field holds a huge number of energetic particles, both electrons and protons. Their energy and concentration depend on the distance to the Earth and geomagnetic latitude. Particles fill, as it were, huge rings or belts covering the Earth around the geomagnetic equator.

Edward Kononovich