How is the earth's magnetic field formed? What is the Earth's magnetic field

The Earth's magnetic field is a formation generated by sources inside the planet. It is the object of study in the corresponding section of geophysics. Next, let's take a closer look at what the Earth's magnetic field is and how it is formed.

general information

Not far from the Earth's surface, approximately at a distance of three of its radii, the lines of force from the magnetic field are located along a system of “two polar charges”. There is an area called the "plasma sphere" here. With distance from the surface of the planet, the influence of the flow of ionized particles from the solar corona increases. This leads to compression of the magnetosphere from the side of the Sun, and, on the contrary, the Earth’s magnetic field is stretched from the opposite, shadow side.

Plasma Sphere

The directional movement of charged particles in the upper layers of the atmosphere (ionosphere) has a noticeable effect on the Earth's surface magnetic field. The location of the latter is one hundred kilometers and above from the surface of the planet. The Earth's magnetic field holds the plasmasphere. However, its structure strongly depends on the activity of the solar wind and its interaction with the confining layer. And frequency magnetic storms on our planet is caused by solar flares.

Terminology

There is a concept "magnetic axis of the Earth". This is a straight line that passes through the corresponding poles of the planet. The "magnetic equator" is the large circle of the plane perpendicular to this axis. The vector on it has a direction close to horizontal. The average strength of the Earth's magnetic field is significantly dependent on geographical location. It is approximately equal to 0.5 Oe, that is, 40 A/m. At the magnetic equator, this same indicator is approximately 0.34 Oe, and near the poles it is close to 0.66 Oe. In some anomalies of the planet, for example, within the Kursk anomaly, the indicator is increased and amounts to 2 Oe. The field lines of the Earth’s magnetosphere with complex structure, projected onto its surface and converging at its own poles, are called “magnetic meridians”.

Nature of occurrence. Assumptions and conjectures

Not long ago, the assumption about the connection between the emergence of the Earth’s magnetosphere and the flow of current in the liquid metal core, located at a distance of a quarter to a third of the radius of our planet, gained the right to exist. Scientists also have an assumption about the so-called “telluric currents” flowing near earth's crust. It should be said that over time there is a transformation of formation. The Earth's magnetic field has changed several times over the past one hundred and eighty years. This is recorded in the oceanic crust, and this is evidenced by studies of remanent magnetization. By comparing areas on both sides of the ocean ridges, the time of divergence of these areas is determined.

Earth's magnetic pole shift

The location of these parts of the planet is not constant. The fact of their displacements has been recorded since the end of the nineteenth century. In the Southern Hemisphere, the magnetic pole shifted by 900 km during this time and ended up in the Indian Ocean. Similar processes are taking place in the Northern part. Here the pole moves towards the magnetic anomaly in Eastern Siberia. From 1973 to 1994, the distance by which the site moved here was 270 km. These pre-calculated data were later confirmed by measurements. According to the latest data, the speed of movement of the magnetic pole Northern Hemisphere has increased significantly. It grew from 10 km/year in the seventies of the last century to 60 km/year at the beginning of this century. At the same time, the strength of the earth's magnetic field decreases unevenly. So, over the past 22 years, in some places it has decreased by 1.7%, and somewhere by 10%, although there are also areas where it, on the contrary, has increased. The acceleration in the displacement of the magnetic poles (by approximately 3 km per year) gives reason to assume that their movement observed today is not an excursion, but another inversion.

This is indirectly confirmed by the increase in the so-called “polar gaps” in the south and north of the magnetosphere. Ionized material from the solar corona and space rapidly penetrates into the resulting expansions. From this, everything is collected in the circumpolar regions of the Earth large quantity energy, which in itself is fraught with additional heating of the polar ice caps.

Coordinates

In the science of cosmic rays, geomagnetic field coordinates are used, named after the scientist McIlwain. He was the first to propose the use of them, since they are based on modified versions of the activity of charged elements in a magnetic field. For a point, two coordinates are used (L, B). They characterize the magnetic shell (McIlwain parameter) and field induction L. The latter is a parameter equal to the ratio of the average distance of the sphere from the center of the planet to its radius.

"Magnetic inclination"

Several thousand years ago, the Chinese made an amazing discovery. They found that magnetized objects can be positioned in a certain direction. And in the middle of the sixteenth century, Georg Cartmann, a German scientist, made another discovery in this area. This is how the concept of “magnetic inclination” appeared. This name refers to the angle of deviation of the arrow up or down from the horizontal plane under the influence of the planet’s magnetosphere.

From the history of research

In the region of the northern magnetic equator, which is different from the geographic equator, the northern end moves downwards, and in the southern, on the contrary, upwards. In 1600, the English physician William Gilbert first made assumptions about the presence of the Earth's magnetic field, which causes a certain behavior of objects that were previously magnetized. In his book, he described an experiment with a ball equipped with an iron arrow. As a result of his research, he came to the conclusion that the Earth is a large magnet. The English astronomer Henry Gellibrant also conducted experiments. As a result of his observations, he came to the conclusion that the Earth's magnetic field is subject to slow changes.

José de Acosta described the possibility of using a compass. He also established how the Magnetic and North Poles differ, and in his famous History(1590) the theory of lines without magnetic deflection was substantiated. Christopher Columbus also made a significant contribution to the study of the issue under consideration. He was responsible for the discovery of the variability of magnetic declination. Transformations are made dependent on changes in geographic coordinates. Magnetic declination is the angle of deviation of the needle from the North-South direction. In connection with the discovery of Columbus, research intensified. Information about what the Earth's magnetic field is was extremely necessary for navigators. M.V. Lomonosov also worked on this problem. To study terrestrial magnetism, he recommended conducting systematic observations using permanent points (similar to observatories). It was also very important, according to Lomonosov, to do this at sea. This idea of the great scientist was realized in Russia sixty years later. The discovery of the Magnetic Pole on the Canadian archipelago belongs to the polar explorer Englishman John Ross (1831). And in 1841 he discovered another pole of the planet, but in Antarctica. The hypothesis about the origin of the Earth's magnetic field was put forward by Carl Gauss. He soon proved that most of it is fed from a source inside the planet, but the reason for its minor deviations is in the external environment.

LIPETSK STATE PEDAGOGICAL INSTITUTE

DEPARTMENT OF THEORETICAL AND GENERAL PHYSICS

Coursework in physics.

DETERMINATION OF THE HORIZONTAL COMPONENT OF THE EARTH'S MAGNETIC FIELD.

Completed by a student of the FPO-3 group

Kazantsev N.N.

Head Associate Professor of the Department of Pacific Physics

Gryzov Yu.V.

LIPETSK

A magnetic field.

A magnetic field is a special form of matter through which interaction occurs between moving electrically charged particles.

Basic properties of the magnetic field:

The magnetic field is generated by electric current (moving charges).

A magnetic field is detected by its action on electricity(moving charges).

The magnetic field was discovered in 1820 by the Danish physicist H.C. Oersted.

The magnetic field is directional and must be characterized by a vector quantity. This quantity is usually denoted by the letter IN . It would be logical by analogy with the electric field strength E name IN magnetic field strength. However, according to historical reasons the main force characteristic of the magnetic field was called magnetic induction . The name “magnetic field strength” turned out to be assigned to an auxiliary characteristic D electric field.

A magnetic field, unlike an electric one, does not affect a charge at rest. Force occurs only when the charge moves.

So, moving charges (currents) change the properties of the space surrounding them - they create a magnetic field in it. This manifests itself in the fact that forces (currents) move in it.

Experience gives. What is true for the magnetic, as well as for the electric? superposition principle:

fieldIN , generated by several moving charges (currents), is equal to the vector sum of the fieldsB I , generated by each charge (current) separately:

II. General characteristics of the earth's magnetic field.

The Earth as a whole is a huge spherical magnet. Humanity began to use the Earth's magnetic field a long time ago. Already at the beginning of the XII-XIII centuries. The compass is becoming widespread in navigation. However, in those days it was believed that the compass needle was oriented by the North Star and its magnetism. The assumption about the existence of the Earth's magnetic field was first expressed in 1600 by the English naturalist Gilbert.

At any point in the space surrounding the Earth and on its surface, the action of magnetic forces is detected. In other words, a magnetic field is created in the space surrounding the Earth, the field lines of which are shown in Fig. 1.

The Earth's magnetic and geographic poles do not coincide with each other. North magnetic pole N lies in southern hemisphere, near the coast of Antarctica, and the south magnetic pole S is located in the Northern Hemisphere, near the northern coast of Victoria Island (Canada). Both poles continuously move (drift) on earth's surface at a rate of about 5 per year due to the variability of the processes generating the magnetic field. In addition, the axis of the magnetic field does not pass through the center of the Earth, but lags behind it by 430 km. The Earth's magnetic field is not symmetrical. Due to the fact that the axis of the magnetic field passes at an angle of only 11.5 degrees to the axis of rotation of the planet, we can use a compass.

The main part of the Earth's magnetic field, according to modern views, is of intraterrestrial origin. The Earth's magnetic field is created by its core. The Earth's outer core is liquid and metallic. Metal is a current-conducting substance, and if there were constant currents in the liquid core, then the corresponding electric current would create a magnetic field. Due to the rotation of the Earth, such currents exist in the core, because The Earth, to some approximation, is a magnetic dipole, i.e. a kind of magnet with two poles: south and north.

A small part of the magnetic field (about 1%) is of extraterrestrial origin. The appearance of this part is attributed to electric currents flowing in the conducting layers of the ionosphere and the Earth's surface. This part of the Earth's magnetic field is subject to a slight change over time, called secular variation. The reasons for the existence of electric currents in secular variation are unknown.

In an ideal and hypothetical assumption, in which the Earth would be alone in outer space, the magnetic field lines of the planet were located in the same way as the field lines of an ordinary magnet from a school physics textbook, i.e. in the form of symmetrical arcs stretching from the south pole to the north. The line density (magnetic field strength) would decrease with distance from the planet. In fact, the Earth's magnetic field interacts with the magnetic fields of the Sun, the planets, and the streams of charged particles emitted in abundance by the Sun. If the influence of the Sun itself, and especially the planets, can be neglected due to their distance, then this cannot be done with particle flows, otherwise the solar wind. The solar wind is a stream of particles rushing at a speed of about 500 km/s emitted by sunny atmosphere. In moments solar flares, as well as during periods of formation of a group of large sunspots on the Sun, the number of free electrons that bombard the Earth’s atmosphere increases sharply. This leads to a disturbance in the currents flowing in the Earth's ionosphere and, due to this, a change in the Earth's magnetic field occurs. Magnetic storms occur. Such flows generate a strong magnetic field, which interacts with the Earth's field, greatly deforming it. Thanks to its magnetic field, the Earth retains captured solar wind particles in the so-called radiation belts, preventing them from passing into the Earth’s atmosphere, much less to the surface. Solar wind particles would be very harmful to all living things. When the mentioned fields interact, a boundary is formed, on one side of which there is a disturbed one (which has undergone changes due to external influences) the magnetic field of solar wind particles, on the other – the disturbed field of the Earth. This boundary should be considered as the limit of near-Earth space, the boundary of the magnetosphere and atmosphere. Beyond this boundary, the influence of external magnetic fields predominates. In the direction of the Sun, the Earth's magnetosphere is flattened under the influence of the solar wind and extends to only 10 radii of the planet. In the opposite direction, there is an elongation of up to 1000 Earth radii.

The bulk of the Earth's magnetic field exhibits anomalies in various areas of the Earth's surface. These anomalies, apparently, should be attributed to the presence of ferromagnetic masses in the earth's crust or to differences in the magnetic properties of rocks. Therefore, the study of magnetic anomalies is of practical importance in the study of minerals.

The existence of a magnetic field at any point on the Earth can be established using a magnetic needle. If you hang a magnetic needle N.S. on a thread l (Fig. 2) so that the suspension point coincides with the center of gravity of the arrow, then the arrow will be installed in the direction of the tangent to the line of force of the Earth’s magnetic field.

In the northern hemisphere - the southern end will be inclined towards the Earth and the arrow will line up with the horizon inclination angleQ (at the magnetic equator the inclination Q equals zero). The vertical plane in which the arrow is located is called the plane of the magnetic meridian. All planes of magnetic meridians intersect in a straight line N.S. , and traces of magnetic meridians on the earth’s surface converge at the magnetic poles N And S . Since the magnetic poles do not coincide with geographic poles, then the arrow will be deviated from the geographic meridian. The angle formed by a vertical plane passing through the arrow (i.e., the magnetic meridian) with the geographic meridian is called magnetic declination a(Fig. 2). Vector

The Earth's magnetic field strength fields can be decomposed into two components: horizontal and vertical (Fig. 3). The values of the inclination and declination angles, as well as the horizontal component, make it possible to determine the magnitude and direction of the total strength of the Earth’s magnetic field at a given point. If the magnetic needle can rotate freely only around a vertical axis, then it will be positioned under the influence of the horizontal component of the Earth's magnetic field in the plane of the magnetic meridian. Horizontal component, magnetic declination a and mood Q are called elements of terrestrial magnetism. All elements of earth's magnetism change over time.

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 the prosperity of 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, then this question has not yet been finally resolved. But most 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. main reason its occurrence is the presence of a liquid core.

Such a phenomenon as magnetism has been known to mankind for a very long time. It got its name from the city of Magnetia, which is located in Asia Minor. It was there that a huge amount of iron ore was discovered. We can find the very first mentions of unique ones in the works of Titus Lucretius Cara, who wrote about this in the poem “On the Nature of Things”, approximately in the 1st century BC.

Since ancient times, people have found use unique properties iron ore. One of the most common devices whose action was based on the attraction of metals was the compass. Now it is very difficult to imagine various industries that would not use simple magnets and electromagnets.

The Earth's magnetic field is the area around the planet that protects it from the harmful effects of radioactive radiation. Scientists still argue about the origin of this field. But most of them believe that it arose due to the Center of our planet having a liquid external and solid internal component. During rotation, the liquid part of the core moves, charged electrical particles move and a so-called magnetic field is formed.

The Earth's magnetic field is also called the magnetosphere. The concept of “magnetism” is a comprehensive and global property of nature. On this moment It is impossible to create a completely complete theory of solar and terrestrial gravity, but science is already trying to figure things out and it manages to give quite convincing explanations of various aspects of this complex phenomenon.

IN Lately Scientists and ordinary citizens are largely concerned that the Earth's magnetic field is gradually weakening its influence. It has been scientifically proven that over the past 170 years the magnetic field has been steadily weakening. This makes you think, since it is a certain kind of shield that protects the Earth and wildlife from the terrible radiation effects sun rays. resists the flow of all such particles that fly towards the poles. All these flows linger in the upper layer of the atmosphere at the poles, forming a wonderful phenomenon - the northern lights.

If suddenly the Earth’s magnetic field disappears or weakens significantly, then everything on the planet will be under the direct influence of cosmic and solar radiation. In turn, this will lead to radiation diseases and damage to all living organisms. The consequence of such a disaster will be terrible mutations or complete destruction. To our great relief, such a development is unlikely.

Paleomagnetologists were able to provide fairly reliable data that the magnetic field is constantly oscillating, and the period of such oscillations varies. They also compiled an approximate curve of field fluctuations and found that at the moment the field is in a descending position and will continue to decline for another couple of thousand years. Then it will begin to intensify again over the course of 4 thousand years. The last maximum value of the magnetic field attraction occurred at the beginning of the current era. The reasons for such instability have been put forward in a variety of ways, but there is no specific theory on this matter.

It has long been known that many magnetic fields have a negative effect on living organisms. For example, experiments carried out on animals have shown that an external magnetic field can delay development, slow down cell growth and even change the composition of the blood. That is why they lead to a deterioration in the health of weather-dependent people.

For humans, a safe magnetic field of the Earth is a field with a strength value of no more than 700 oersteds. It is worth noting that we're talking about not about the Earth’s magnetic field itself, but about the electromagnetic fields that are formed during the operation of any radio and electrical device.

The physical side of the process of the influence of the Earth’s magnetic field on humans is still not entirely clear. But we managed to find out that it affects plants: germination and further growth of seeds directly depend on their initial orientation in relation to the magnetic field. Moreover, its change can either accelerate or slow down the development of the plant. It is quite possible that someday this property will be used in agriculture.

Earth is the force of its attraction. It varies in some places, but the average is 0.5 oersted. In some places (in the so-called tension increases to 2E.

IN last days A large amount of news about the Earth's magnetic field has appeared on scientific information sites. 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?

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. His South Pole is located at the geographic North Pole, and the northern one, accordingly, 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 earthly inhabitants).

Scientists do not rule out that some of the planets earth type do not have a metal core and, accordingly, are devoid of 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 two possible mechanisms for the formation of “rocky” planets without a core. If the theoretical calculations of the researchers are confirmed by observations, then the formula for calculating the probability of meeting humanoids in the Universe, or at least something reminiscent of illustrations from a biology textbook, will have to be rewritten.

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. Last time this event occurred about 720 thousand years ago.

The change of poles is accompanied by a change in the configuration of the magnetic field. During " transition period"Significantly more cosmic particles, 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. Analysis of data on his condition over several years showed that in recent months Dangerous changes began to occur within 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 southern part 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.

At the moment, it is difficult 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, they find the road, focusing specifically on it. There are several hypotheses explaining how exactly they sense the field. One of the latest suggests that birds perceive the magnetic field visually. 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 the analysis showed satellite photos presented within the project Google Earth, cows. After studying photographs of 8,510 cows in 308 areas of the world, scientists concluded that these animals preferentially orient their bodies from north to south (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 to the appearance of auroras. 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. "Collected" particles accumulate in certain parts fields - 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, astronauts would receive lethal dose radiation.

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.

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 region is called the Earth's plasmasphere.

As you move away from the Earth's surface, the influence of the solar wind increases: on the side of the Sun, the geomagnetic field compresses, and on 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 region of the upper atmosphere extends 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 strength at points of the magnetic equator has an approximately horizontal direction.

The average field strength at the Earth's surface is about 0.5 Oe (40 A/m) and is highly dependent on geographic location. The magnetic field strength at the magnetic equator is about 0.34 Oe (Oersted), at the magnetic poles it is about 0.66 Oe. In some areas (in the so-called areas of magnetic anomalies), tension increases sharply. In the area of the Kursk magnetic anomaly it reaches 2 Oe.

The Earth's dipole magnetic moment in 1995 was 7.812x10 25 G cm 3 (or 7.812x10 22 A m 2), decreasing on average over recent decades by 0.004x10 25 G cm 3 or 1/4000 per year.

A common approximation of the Earth's magnetic field is in the form of a harmonic series - the Gaussian series.

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 pulsations 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 calculated that the zone in which the “magnetic dynamo” mechanism operates is located at a distance of 0.25-0.3 radii of the Earth. 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

Studies of remanent magnetization acquired by igneous rocks when they cool below the Curie point, indicate repeated inversions of the Earth's magnetic field, recorded in strip magnetic anomalies of the oceanic crust, parallel to the axes of the mid-ocean ridges.

Formation of strip magnetic anomalies during spreading.

Shift of the Earth's magnetic poles

The displacement of 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 reached Indian Ocean. The latest data on the state of the Arctic magnetic pole (moving towards the East Siberian world magnetic anomaly through Arctic Ocean) showed that from 1973 to 1984 its mileage was 120 km, from 1984 to 1994 - more than 150 km. Although these data are calculated, they are confirmed by measurements of the north magnetic pole. According to data at the beginning of 2007, the drift speed of the north magnetic pole increased from 10 km/year in the 70s to 60 km/year in 2004.

The strength of the earth's magnetic field is falling, and unevenly. Over the past 22 years, it has decreased by an average of 1.7%, and in some regions - for example, in the South Atlantic Ocean - by 10 percent. In some places, the magnetic field strength, contrary to the general trend, even increased.

The acceleration of the movement of the poles (on average by 3 km/year) and their movement along the corridors of magnetic pole inversion (more than 400 paleoinversions made it possible to identify these corridors) suggests that this movement of the poles should be seen not as an excursion, but as another inversion of 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-90s. 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.

In the past, magnetic pole reversals occurred many times and life was preserved. The question is at what cost. If, as some hypotheses state, the Earth's magnetosphere disappears for some time during a reversal of the poles, then a stream of cosmic rays will fall on the Earth, which poses a danger to land dwellers, and even more so if the disappearance of the magnetosphere is associated with depletion of the ozone layer. It is encouraging that during the reversal of the solar magnetic field that occurred in March 2001, the complete disappearance of the solar magnetosphere was not recorded. The full cycle of revolution of the Sun's magnetic field is 22 years.

Geomagnetic coordinates (McIlwain coordinates)

In cosmic ray physics, specific coordinates in the geomagnetic field, named after the scientist Carl McIlwain who first proposed their use, are widely used, since they are based on 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 McIlwain parameter (English L-shell, L-value, McIlwain L-parameter), B is the magnetic induction of the field (usually in Gs). 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 in 1600 in his book “On the Magnet” (“De Magnete”), in which he described the 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 by English astronomer Henry Gellibrand showed that the geomagnetic field is not constant, but changes slowly.

José de Acosta (one of the Founders of Geophysics, according to Humboldt) in his History (1590) first appeared the theory of four lines without magnetic declination (he described the use of a compass, the angle of deflection, the differences between Magnetic and North Pole; although deviations were known as early as the 15th century, he described the fluctuation of deviations from one point to another; he identified places with zero deviation: for example, in the Azores).

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 geographical coordinates. Columbus's discovery gave impetus to a new study of the Earth's magnetic field: information about it was needed by sailors. In 1759, the Russian scientist M.V. Lomonosov, in his report “Discourse on the Great Accuracy of the Sea Route,” gave valuable advice 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.