Magnetic shell of the earth. Earth's magnetic field

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

Also in 1905, the French geophysicist Bernard Brunhes carried out measurements of 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 vector magnetic field(his compatriot P. David obtained similar results even a year earlier). Brunhes came to the conclusion that three quarters of a million years ago, during the outpouring of lava, the direction of the geomagnetic field lines was opposite to the modern one. This is how the effect of inversion (reversal of polarity) of the Earth's magnetic field was discovered. In the second half of the 1920s, Brunhes's conclusions were confirmed by P. L. Mercanton and Monotori Matuyama, but these ideas received recognition 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 have swapped places thousands of times (Brunhes and Matuyama studied the most recent reversal, which now bears their names). Sometimes the geomagnetic field maintains its orientation for tens of millions of years, and sometimes for no more than five hundred centuries. The inversion process itself usually takes several thousand years, and upon completion, the field strength, as a rule, does not return to its previous value, but changes by several percent.

Mechanism geomagnetic inversion is not entirely clear to this day, and even a hundred years ago it did not admit of 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 it was studied by such stars of European science as great traveler Alexander von Humboldt, the brilliant mathematician Carl Friedrich Gauss and the brilliant experimental physicist Wilhelm Weber. So Einstein truly 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 pole. Geographic poles are considered to be the points of intersection of the earth's axis with the surface of the planet. Because the Earth rotates like solid, there are only two such points and nothing else can be thought of. 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 field lines are perpendicular earth's surface. However, any magnetometer records not only the planetary magnetic field, but also the fields of local rocks, ionospheric electric currents, solar wind particles and other additional sources of magnetism (and their average share is not so small, on the order of several percent). The more accurate the device, the better it does this - and therefore makes it increasingly 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 pole coordinates determined using direct measurement, are not stable even over 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. To a first approximation, our planet can be considered a geocentric magnetic dipole, the axis of which passes through its center. Currently, the angle between it and the earth's axis is 10 degrees (several decades ago it was more than 11 degrees). With more accurate modeling, it turns out that the dipole axis is shifted relative to the center of the Earth towards the northwestern part of the Pacific Ocean by about 540 km (this is an eccentric dipole). There are other definitions.

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

Poles in reverse

Many people know that common names The poles are exactly the opposite. In the Arctic there is a pole to which the northern end of the magnetic needle points - therefore, it should be considered southern (like poles repel, opposite poles attract!). Likewise, the magnetic north pole is based at high latitudes in the Southern Hemisphere. However, traditionally we name the poles according to geography. Physicists have long agreed that lines of force come out of the north pole of any magnet and enter the south. It follows that the lines of earth's magnetism leave the south geomagnetic pole and are drawn towards the north. This is the convention, and you shouldn’t violate it (it’s time to remember Panikovsky’s sad experience!).

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

As Lawrence Newitt, the former head of the geomagnetic laboratory of the Canadian Geological Research Service, told Popular Mechanics, the true pole is now 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 end up in Siberia. According to the reconstruction carried out several years ago by the same Newitt, in the 17th and XVIII centuries The magnetic north pole moved predominantly to the southeast and only turned to the northwest around 1860. 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 even come from? One possible explanation is simply glaring. The Earth has an inner solid iron-nickel core, the radius of which is 1220 km. Since these metals are ferromagnetic, why not assume that the inner core has 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. Polar migration and geomagnetic field reversals are more difficult to explain, but we can probably try.

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

Let's consider another possibility. Our planet also has a liquid outer core approximately 2,300 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

“To explain the appearance of the poloidal field, it is necessary to take into account the vertical flows of matter in the nucleus. They are formed due to convection: heated iron-nickel melt floats up from the lower part of the core towards the mantle. These jets are twisted by the Coriolis force like air currents of cyclones. In the Northern Hemisphere, updrafts rotate clockwise, while in the Southern Hemisphere they rotate counterclockwise, explains University of California professor Gary Glatzmeier. - When approaching the mantle, the core material cools down and begins to move back inward. The magnetic fields of the ascending and descending flows cancel each other, 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, the field lines, which faced west before convective ascent, rotate clockwise by 90 degrees and are oriented 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 emergence of the poloidal field, it is considered the most likely.”

This is precisely the scheme that geophysicists discussed 80 years ago. They believed that the flows of the conducting fluid of the outer core, due to their kinetic energy, generate electric currents, covering the earth's axis. These currents generate a magnetic field of predominantly dipole type, the field lines of which on the Earth's surface are elongated along the meridians (such a field is called poloidal). This mechanism evokes an association with the operation of a dynamo, hence its name.

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

“We don’t know exactly when Earth’s magnetism arose, but it could have happened soon after the formation of the mantle and outer core,” says David Stevenson, one of the leading experts on planetary magnetism, a 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 taken on 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. If there is such a field and circular motion flows of conducting fluid, the launch of the intraplanetary dynamo became simply inevitable.”

Magnetic protection

Earth's magnetism is monitored using an extensive network of geomagnetic observatories, the creation of which began in the 1830s.

For the same purposes, shipborne, aviation and space instruments are used (for example, scalar and vector magnetometers of the Danish Ørsted satellite, operating since 1999).

Geomagnetic field strengths range from approximately 20,000 nanoteslas off the coast of Brazil to 65,000 nanoteslas near the south magnetic pole. Since 1800, its dipole component has decreased by almost 13% (and since the mid-16th century by 20%), while its quadrupole component has increased slightly. Paleomagnetic studies show that for several thousand years before the beginning of our era, the intensity of the geomagnetic field persistently 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, the results of paleomagnetic measurements were published indicating that 3.5 billion years ago the Earth’s magnetic field was half as strong as it is today). This means that the whole story human societies from the emergence of the first states to our time fell on a local maximum of the earth's magnetic field. It is interesting to think about whether this has affected the progress of civilization. This assumption ceases to seem fantastic if we consider that the magnetic field protects the biosphere from cosmic radiation.

And here is one more circumstance that is worth noting. In our planet’s youth and even adolescence, all the matter in its core was in the liquid phase. The solid inner core formed relatively recently, perhaps only a billion years ago. When this happened, the convection currents became more orderly, which led to 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 had a beneficial effect on the evolution of living organisms. In particular, the strengthening of geomagnetism improved the protection of the biosphere from cosmic radiation and thereby facilitated the exit of life from the ocean to land.

Here is the generally accepted explanation for such a launch. For simplicity, let the seed field be almost parallel to the Earth's rotation axis (in fact, it is sufficient if it has a non-zero component in this direction, which is almost inevitable). The speed of rotation of the material 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 force lines of the seed field will bend, going forward at greater depths and falling 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 span 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, there has long been an adequate explanation for geomagnetism mathematical apparatus- equations of magnetic hydrodynamics 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's exactly what Roberts and I did. A run on a supercomputer made it possible to construct a self-consistent description of the long-term evolution of the speed, temperature and pressure of matter flows in the outer core and the associated evolution of magnetic fields. We also found out that if we play the simulation over time intervals of the order of tens and hundreds of thousands of years, then geomagnetic field inversions inevitably occur. So in this respect, our model does a good job of conveying the planet's magnetic history. However, there is a difficulty that has not yet been resolved. The parameters of the material 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 would not be enough. In fact, this is not the case; there is every reason to believe that it almost coincides with the viscosity of water. Our current models are powerless to take into account turbulence, which undoubtedly occurs. But computers are gaining strength every year, and in ten years there will be much more realistic simulations.”

“The operation of a geodynamo is inevitably associated with chaotic changes in the flow of iron-nickel melt, which result in fluctuations in magnetic fields,” adds Professor Stevenson. - Inversions of terrestrial magnetism are simply the strongest possible fluctuations. Since they are stochastic in nature, they can hardly be predicted in advance - at least we don’t know how to do so.”

IN last days appeared on scientific information sites a large number of news about the Earth's magnetic field. For example, news that it has been changing significantly recently, or that the magnetic field contributes to the leakage of oxygen from the earth’s atmosphere, or even that cows in pastures are oriented along the lines of the magnetic field. What is a magnetic field and how important is all this news?

The Earth's magnetic field is the area around our planet where magnetic forces operate. The question of the origin of the magnetic field has not yet been completely 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 interior and a liquid exterior. The rotation of the Earth creates constant currents in the liquid core. As the reader may remember from physics lessons, motion electric charges leads to the appearance of 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 maintenance of 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 its north pole, respectively, is at the South Pole. In fact, the geographic and magnetic poles of the Earth do not coincide not only in “direction”. The magnetic field axis is tilted relative to the Earth's rotation axis by 11.6 degrees. Since the difference is not very significant, we can use a compass. Its arrow points precisely to the Earth's South Magnetic Pole and almost exactly to the North Geographic Pole. If the compass had been invented 720 thousand 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) solar wind particles. The magnetic field changes the trajectory of their movement, directing the particles along the field lines. The necessity of a magnetic field for the existence of life narrows the range of potentially habitable planets (if we proceed from the assumption that hypothetically possible life forms are similar to terrestrial inhabitants).

Scientists do not rule out that some terrestrial planets do not have a metallic core and, accordingly, lack a magnetic field. Until now, planets made of solid rock, like Earth, were thought to contain three main layers: a solid crust, a viscous mantle, and a solid or molten iron core. In a recent paper, scientists from the Massachusetts Institute of Technology proposed the formation of "rocky" planets without a core. If the theoretical calculations of the 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, it will be necessary to rewrite them.

Earthlings may also lose their magnetic protection. True, geophysicists cannot yet say exactly when this will happen. The fact is that the Earth's magnetic poles are not constant. Periodically they change places. Not long ago, researchers found that the Earth “remembers” the reversal of the poles. 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 occurred was about 720 thousand years ago.

The change of poles is accompanied by a change in the configuration of the magnetic field. During the “transition period,” significantly more cosmic particles that are dangerous to living organisms penetrate to Earth. One of the hypotheses explaining the disappearance of dinosaurs states that the giant reptiles became extinct precisely during the next pole change.

In addition to the “traces” of planned activities to change the poles, researchers noticed dangerous shifts in the Earth’s magnetic field. An analysis of data on his condition over several years showed that in recent months, things began to happen to 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 area does not exceed a third of the "normal" one. Researchers have long noticed this “hole” in the Earth’s magnetic field. Data collected over 150 years show that the field here has weakened by ten percent over this period.

On this moment It’s hard to say what threat this poses to humanity. One of the consequences of weakening the field strength may be an increase (albeit insignificant) in the oxygen content in 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 explaining how exactly they sense the field. One of the latest 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 an analysis of satellite photographs presented as part of the Google Earth project showed, cows. After studying photographs of 8,510 cows in 308 areas of the world, scientists concluded that these animals preferentially (or from south to north). Moreover, the “reference points” for cows are not geographical, but rather the magnetic poles of the Earth. The mechanism by which cows perceive the magnetic field and the reasons for this particular reaction to it remain unclear.

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

The magnetic field was not ignored by supporters of one of the “conspiracy theories” - the theory of a 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 the moon landings believe that astronauts would have received a lethal dose of radiation during their flight through the radiation belts.

The Earth's magnetic field is an amazing consequence of the laws of physics, a protective shield, a landmark and the creator of auroras. If it weren't for it, life on Earth might have looked completely different. In general, if there were no magnetic field, it would have to be invented.

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

The magnetic field extends to an altitude 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 sunlit side of the Earth, the magnetosphere is limited spherical surface with a radius of approximately 10-15 Earth radii, and on the opposite side it is extended like a comet’s 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 relative to the earth's rotation axis by 12°. It is located approximately 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 Earth's magnetic poles do not coincide with the true geographic poles. Currently, the coordinates of the magnetic poles are as follows: north - 77° north latitude. 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

Lines of force running from one magnetic pole to another are called magnetic meridians. An angle is formed between the magnetic and geographic meridians, called magnetic declination. Every place on Earth has its own declination angle. In the Moscow region the declination angle is 7° to the east, and in Yakutsk it is 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 geographical one. If you move north of the magnetic equator, the northern end of the needle will gradually descend. 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 its northern end down, and at the South Magnetic Pole its southern 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, it moves 15 km in one year. IN last years the speed of movement of the magnetic poles increased sharply. 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.

For geological history Our planet's magnetic field has changed its polarity more than 100 times.

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

There are daily variations in the Earth's magnetic field. The reason for these changes in the Earth's magnetic field is electric currents flowing in the atmosphere at high altitudes. They are caused by solar radiation. Under the influence of the solar wind, the Earth's magnetic field is distorted and acquires a “trail” in the direction from the Sun, which extends for hundreds of thousands of kilometers. The main cause of the solar wind, as we already know, is the enormous ejections of matter from the solar corona. As they move towards the Earth, they turn into magnetic clouds and lead to strong, sometimes extreme disturbances on the Earth. Particularly strong disturbances of the Earth's magnetic field - magnetic storms. Some magnetic storms begin suddenly and almost simultaneously across the entire Earth, while others develop gradually. They can last for several hours or even days. Often magnetic storms occur 1-2 days after 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 latitude 66-67° (in the aurora zone) and occur simultaneously with 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. Over 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 dayside penetrates into the magnetosphere and then into the upper atmosphere. During magnetic storms, particles from the tail of the magnetosphere rush here, reaching the boundaries upper atmosphere in high latitudes of 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 creating permanent magnetism 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 caused by sources located in the depths of the Earth. They can be roughly divided into two groups. The main part of them is associated with processes in the earth's core, where, due to continuous and regular movements of electrically conductive matter, a system of electric currents is created. The other is due to the fact that rocks earth's crust, magnetized by the main electric field(field of the core), create their own magnetic field, which is summed with the magnetic field of the core.

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

Gravitational 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 the shape of an ellipsoid of revolution and 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 a gravity anomaly. Different material composition and density of rocks cause these anomalies. But other reasons are also possible. They can be explained by the following process - the equilibrium 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, movement lithospheric plates and thereby create the macrorelief of the Earth. Gravity holds the atmosphere, hydrosphere, people, animals on Earth. Gravity must be taken into account when studying processes in geographical envelope. The term " geotropism" are the growth movements of plant organs, which, under the influence of the force of gravity, always ensure the vertical direction of growth of the primary root perpendicular to the surface of the Earth. Gravity biology uses plants as experimental subjects.

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, impossible further development astronomy, physics and other sciences.

What the Earth's magnetic field is needed for, you will learn from this article.

What is the value of the Earth's magnetic field?

First of all, it protects artificial satellites and the inhabitants of the planet from the action of particles from space. These include charged, ionized particles of the solar wind. When they enter our atmosphere, the magnetic field changes their trajectory and directs them along the field line.

In addition, we entered the era of new technologies thanks to our magnetic field. All modern, advanced devices that operate using a variety of memory storage devices (disks, cards) depend directly on the magnetic field. Its tension and stability directly affects absolutely all information, computer systems, since all the information necessary for their proper operation is located on magnetic media.

Therefore, we can say with confidence that prosperity modern civilization, the “viability” of its technologies closely depends on the state of the magnetic field of our planet.

What is the Earth's magnetic field?

Earth's magnetic field is the area around the planet where magnetic forces act.

As for its origin, this issue has not yet been finally resolved. But most of Researchers are inclined to believe that our planet owes its magnetic field to its core. It consists of an inner solid and an outer liquid part. The rotation of the Earth contributes to constant currents in the liquid core. And this leads to the emergence of a magnetic field around them.

Most of the planets solar system have magnetic fields to varying degrees. If you place them in a row in order of decreasing magnetic dipole moment, you will get the following picture: Jupiter, Saturn, Earth, Mercury and Mars. The main reason for its occurrence is the presence of a liquid core.

Structure and characteristics of the Earth's magnetic field

At a small distance from the Earth's surface, about three of its radii, magnetic field lines have a dipole-like arrangement. This area is called plasmasphere Earth.

As you move away from the Earth's surface, the influence of the solar wind increases: from the side of the Sun, the geomagnetic field is compressed, and from the opposite, night side, it stretches into a long “tail”.

Plasmosphere

Currents in the ionosphere have a noticeable effect on the magnetic field on the Earth's surface. This is the region of the upper atmosphere, extending from altitudes of about 100 km and above. Contains a large number of ions. The plasma is held by the Earth's magnetic field, but its state is determined by the interaction of the Earth's magnetic field with the solar wind, which explains the connection between magnetic storms on Earth and solar flares.

Field Options

Points on the Earth at which the magnetic field strength has a vertical direction are called magnetic poles. There are two such points on Earth: the north magnetic pole and the south magnetic pole.

The straight line passing through the magnetic poles is called the Earth's magnetic axis. The great circle in a plane that is perpendicular to the magnetic axis is called the magnetic equator. The magnetic field vector at points of the magnetic equator has an approximately horizontal direction.

The Earth's magnetic field is characterized by disturbances called geomagnetic pulsations due to the excitation of hydromagnetic waves in the Earth's magnetosphere; The frequency range of ripples extends from millihertz to one kilohertz.

Magnetic meridian

Magnetic meridians are the projections of the Earth's magnetic field lines onto its surface; complex curves converging at the Earth's north and south magnetic poles.

Hypotheses about the nature of the Earth's magnetic field

Recently, a hypothesis has been developed that links the emergence of the Earth's magnetic field with the flow of currents in the liquid metal core. It is estimated that the zone in which the “magnetic dynamo” mechanism operates is located at a distance of 0.25-0.3 Earth radii. A similar field generation mechanism may take place on other planets, in particular, in the cores of Jupiter and Saturn (according to some assumptions, consisting of liquid metallic hydrogen).

Changes in the Earth's magnetic field

This is confirmed by the current increase in the opening angle of the cusps (polar gaps in the magnetosphere in the north and south), which reached 45° by the mid-1990s. Radiation material from the solar wind, interplanetary space and cosmic rays, as a result of which more matter and energy enter the polar regions, which can lead to additional heating of the polar caps.

Geomagnetic coordinates (McIlwain coordinates)

Cosmic ray physics widely uses specific coordinates in the geomagnetic field, named after the scientist Carl McIlwain ( Carl McIlwain), who was the first to propose their use, since they are based on the invariants of particle motion in a magnetic field. A point in a dipole field is characterized by two coordinates (L, B), where L is the so-called magnetic shell, or the McIlwain parameter. L-shell, L-value, McIlwain L-parameter ), B - magnetic field induction (usually in G). The parameter of the magnetic shell is usually taken to be the value L, equal to the ratio of the average distance of the real magnetic shell from the center of the Earth in the plane of the geomagnetic equator to the radius of the Earth. .

History of research

The ability of magnetized objects to be located in a certain direction was known to the Chinese several thousand years ago.

In 1544, the German scientist Georg Hartmann discovered magnetic inclination. Magnetic inclination is the angle by which the needle, under the influence of the Earth's magnetic field, deviates from the horizontal plane down or up. In the hemisphere north of the magnetic equator (which does not coincide with the geographic equator), the northern end of the arrow deviates downward, in the southern - vice versa. At the magnetic equator itself, the magnetic field lines are parallel to the Earth's surface.

The first assumption about the presence of the Earth's magnetic field, which causes such behavior of magnetized objects, was made by the English physician and natural philosopher William Gilbert. William Gilbert) in 1600 in his book “On the Magnet” (“De Magnete”), in which he described an experiment with a ball of magnetic ore and a small iron arrow. Gilbert came to the conclusion that the Earth is a large magnet. Observations of the English astronomer Henry Gellibrand. Henry Gellibrand) showed that the geomagnetic field is not constant, but changes slowly.

The angle by which the magnetic needle deviates from the north-south direction is called magnetic declination. Christopher Columbus discovered that magnetic declination does not remain constant, but changes with changes in geographic coordinates. Columbus's discovery gave impetus to a new study of the Earth's magnetic field: information about it was needed by sailors. The Russian scientist M.V. Lomonosov in 1759, in his report “Discussion on the great accuracy of the sea route,” gave valuable advice, allowing you to increase the accuracy of compass readings. To study terrestrial magnetism, M.V. Lomonosov recommended organizing a network of permanent points (observatories) in which to carry out systematic magnetic observations; Such observations must be carried out widely at sea. Lomonosov's idea of ​​organizing magnetic observatories was realized only 60 years later in Russia.

In 1831, the English polar explorer John Ross discovered the magnetic pole in the Canadian archipelago - the region where the magnetic needle occupies a vertical position, that is, the inclination is 90°. In 1841, James Ross (nephew of John Ross) reached the other magnetic pole of the Earth, located in Antarctica.

Carl Gauss (German) Carl Friedrich Gauß) put forward a theory about the origin of the Earth's magnetic field and in 1839 proved that the main part of it comes out of the Earth, and the reason for small, short deviations in its values ​​must be sought in the external environment.

see also

• Intermagnet ( English)

Notes

Literature

• Sivukhin D.V. General course physics. - Ed. 4th, stereotypical. - M.: Fizmatlit; Publishing house MIPT, 2004. - T. III. Electricity. - 656 s. - ISBN 5-9221-0227-3; ISBN 5-89155-086-5.
• Koshkin N.I., Shirkevich M.G. Handbook of elementary physics. - M.: Science, 1976.
• N. V. Koronovsky Magnetic field of the Earth's geological past. Soros Educational Journal, N5, 1996, p. 56-63

Links

Maps of the displacement of the Earth's magnetic poles for the period from 1600 to 1995

Other information on the topic

• Magnetic field reversals in the geological history of the Earth
• The influence of magnetic field reversal on climate and the evolution of life on Earth

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See what “Earth’s magnetic field” is in other dictionaries: To distances? 3R= (R= radius of the Earth) corresponds approximately to the field of a uniformly magnetized ball with field strength? 55 7 A/m (0.70 Oe) at the magnetic poles of the Earth and 33.4 A/m (0.42 Oe) at the magnetic equator. At distances 3R magnetic field... ...

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