How does the earth's magnetic field work. Magnetic field What determines the change in the geomagnetic field of the earth

Let's understand together what a magnetic field is. After all, many people live in this field all their lives and do not even think about it. Time to fix it!

A magnetic field

A magnetic field is a special kind of matter. It manifests itself in the action on moving electric charges and bodies that have their own magnetic moment (permanent magnets).

Important: a magnetic field does not act on stationary charges! A magnetic field is also created by moving electric charges, or by a time-varying electric field, or by the magnetic moments of electrons in atoms. That is, any wire through which current flows also becomes a magnet!

A body that has its own magnetic field.

A magnet has poles called north and south. The designations "northern" and "southern" are given only for convenience (as "plus" and "minus" in electricity).

The magnetic field is represented by force magnetic lines. The lines of force are continuous and closed, and their direction always coincides with the direction of the field forces. If metal shavings are scattered around a permanent magnet, the metal particles will show a clear picture of the magnetic field lines emerging from the north and entering the south pole. Graphical characteristic of the magnetic field - lines of force.

Magnetic field characteristics

The main characteristics of the magnetic field are magnetic induction, magnetic flux And magnetic permeability. But let's talk about everything in order.

Immediately, we note that all units of measurement are given in the system SI.

Magnetic induction B - vector physical quantity, which is the main power characteristic of the magnetic field. Denoted by letter B . The unit of measurement of magnetic induction - Tesla (Tl).

Magnetic induction indicates how strong a field is by determining the force with which it acts on a charge. This force is called Lorentz force.

Here q - charge, v - its speed in a magnetic field, B - induction, F is the Lorentz force with which the field acts on the charge.

F- a physical quantity equal to the product of magnetic induction by the area of the contour and the cosine between the induction vector and the normal to the plane of the contour through which the flow passes. Magnetic flux is a scalar characteristic of a magnetic field.

We can say that the magnetic flux characterizes the number of magnetic induction lines penetrating a unit area. The magnetic flux is measured in Weberach (Wb).

Magnetic permeability is the coefficient that determines the magnetic properties of the medium. One of the parameters on which the magnetic induction of the field depends is the magnetic permeability.

Our planet has been a huge magnet for several billion years. The induction of the Earth's magnetic field varies depending on the coordinates. At the equator, it is about 3.1 times 10 to the minus fifth power of Tesla. In addition, there are magnetic anomalies, where the value and direction of the field differ significantly from neighboring areas. One of the largest magnetic anomalies on the planet - Kursk And Brazilian magnetic anomaly.

The origin of the Earth's magnetic field is still a mystery to scientists. It is assumed that the source of the field is the liquid metal core of the Earth. The core is moving, which means that the molten iron-nickel alloy is moving, and the movement of charged particles is the electric current that generates the magnetic field. The problem is that this theory geodynamo) does not explain how the field is kept stable.

The earth is a huge magnetic dipole. The magnetic poles do not coincide with the geographic ones, although they are in close proximity. Moreover, the Earth's magnetic poles are moving. Their displacement has been recorded since 1885. For example, over the past hundred years, the magnetic pole in the Southern Hemisphere has shifted by almost 900 kilometers and is now in the Southern Ocean. The pole of the Arctic hemisphere is moving across the Arctic Ocean towards the East Siberian magnetic anomaly, the speed of its movement (according to 2004 data) was about 60 kilometers per year. Now there is an acceleration of the movement of the poles - on average, the speed is growing by 3 kilometers per year.

What is the significance of the Earth's magnetic field for us? First of all, the Earth's magnetic field protects the planet from cosmic rays and the solar wind. Charged particles from deep space do not fall directly to the ground, but are deflected by a giant magnet and move along its lines of force. Thus, all living things are protected from harmful radiation.

During the history of the Earth, there have been several inversions(changes) of magnetic poles. Pole inversion is when they change places. The last time this phenomenon occurred about 800 thousand years ago, and there were more than 400 geomagnetic reversals in the history of the Earth. Some scientists believe that, given the observed acceleration of the movement of the magnetic poles, the next pole reversal should be expected in the next couple of thousand years.

Fortunately, no reversal of poles is expected in our century. So, you can think about the pleasant and enjoy life in the good old constant field of the Earth, having considered the main properties and characteristics of the magnetic field. And so that you can do this, there are our authors, who can be entrusted with some of the educational troubles with confidence in success! and other types of work you can order at the link.

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 about 10-15 Earth radii, and on the opposite side it is elongated like a cometary tail to 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 in Moscow deviates by T to the right of the geographical 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. In recent 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 electric currents flowing in the atmosphere at 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 also rush here during magnetic storms, reaching the boundaries of the upper atmosphere at 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 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 core), create their own magnetic field, which is added to the magnetic field of the core.

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”call 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 spacecraft, to make a gravimetric exploration of ore minerals, and, finally, the further development of astronomy, physics and other sciences is impossible.

Always wondered how the compass works? And today we will talk about such a thing as the MAGNETIC FIELD of the EARTH. And since, unfortunately, the editor is limited in time, and I want to give something interesting, we will tell you about “terrestrial magnetism” using several different sources.

So:

The Earth's magnetic field has long been a mystery, because there are no stone magnets, right? But as soon as you discover that there is a colossal amount of iron inside the Earth, everything seems to fall into place. Iron does not form a "permanent" magnet, like those attached to plastic piglets and bear cubs, which we ourselves, without knowing why, buy to attach to the refrigerator. The bowels of the earth are more like a dynamo. By the way, this is what is called - geomagnetic dynamo. As we have already mentioned, the iron in the core of the Earth is mostly in a molten state, with the exception of a solid, dense "ball" in the very center. The liquid part still continues to heat up. Previously, this phenomenon was explained by the fact that radioactive elements, being denser than anything else in the chemical composition of the planet, plunged into the very center, being locked there, and the radioactive energy emitted by them gives heat. The modern theory offers a completely different explanation: the liquid part of the nucleus heats up, since the solid part cools down. Molten iron on contact with a solid core solidifies itself little by little, while heat is released. That heat has to go somewhere, it can't just disappear like a puff of warm air around a thousand miles of solid rock. Heat is transferred to the molten layer of the core, heating it.

It may surprise you that the part that comes into contact with the solid core can cool and solidify and, at the same time, heat up during this solidification. The explanation is simple: hot molten iron rises as it heats up. Remember the balloon. When you heat air, it rises. This is because when heated, the air expands, becomes less dense, and less dense substances float above denser ones. The balloon holds the air in a huge silk bag, often brightly colored and emblazoned with bank or real estate emblems, and rises with the air. Hot iron is unpainted, but rises in the same way as hot air, moving away from a solid core. It floats slowly, cooling down, and then, when it gets too cold, more precisely relatively cold, begins to sink into the depths again. As a result, the earth's core is in constant motion, heating up inside and cooling down outside. It cannot rise all at once, that is, some areas of the core rise, while others sink again. This kind of circulating heat transfer is called convection.

According to physicists, under certain three conditions, moving liquids can create a magnetic field. First, the liquid must conduct electricity, and iron does an excellent job of this. Secondly, at least a small magnetic field must initially be present, and there are good reasons to believe that our Earth, then still very young, had a certain amount of personal magnetism. Thirdly, something must rotate this liquid, distorting the original magnetic field, and for the Earth such rotation occurs due to the Coriolis force, similar to centrifugal force, but acting more weakly and resulting from the rotation of the Earth around its axis. Roughly speaking, the rotation distorts the initially weak magnetic field, twisting it like spaghetti on a fork. Then the magnetism rises up, caught by the floating masses of the iron core. As a result of all this rotation, the magnetic field becomes much stronger.

Yes, in a sense, you can say that the Earth behaves as if it has a huge magnet inside it, but in fact, everything is much more complicated. To flesh out the picture a little, let's recall that there are at least seven other factors that determine the presence of a magnetic field in the Earth. So, some components of the earth's crust can be permanent magnets. Like a compass needle pointing north, they gradually lined up along the stronger geomagnetic dynamo, further strengthening it. In the upper layers of the atmosphere there is a layer of charged ionized gas. Before satellites were invented, the ionosphere played a critical role in radio communications: radio waves bounced off charged gas instead of escaping into space. The ionosphere is in motion, and moving electricity creates a magnetic field. At an altitude of about 15,000 miles (24,000 km), a ring current flows, a layer of low-density ionized particles that forms a huge torus. This slightly weakens the strength of the Earth's magnetic field.

The next two factors are the so-called magnetopause and the magnetic tail, which have arisen under the influence of the solar wind on the Earth's magnetosphere. The solar wind is a constant stream of particles emitted by a hyperactive Sun. The magnetopause is the bow wave of the earth's magnetic field, going against the solar wind, and the magnetic tail is the trace of this wave from the opposite side of the planet, where the Earth's own magnetic field "leaks" outward, besides being destroyed under the influence of the solar wind. In addition, the solar wind causes a kind of thrust along the Earth's orbit, creating an additional distortion of the magnetic field lines, known as field-aligned current in the magnetosphere. And finally, there are auroral flows. The Northern Lights, or aurora borealis, are delightful, mysterious sheets of pale light shimmering in the northern polar sky. A similar spectacle, aurora australis, can be seen near the South Pole. Auroras are created by two bands of electric current flowing from the magnetopause into the magnetic tail. This, in turn, creates new magnetic fields and two electrical currents - western and eastern.

So you're saying the Earth is just a big magnet? Well, yes, and the ocean is a bowl of water.

Magnetic materials found in ancient rocks testify that from time to time the Earth's magnetic field changes its polarity, the north magnetic pole becomes south and vice versa. This happens about once every half a million years, although a strict pattern could not be traced. No one knows exactly why this happens, but mathematical models show that the Earth's magnetic field can be oriented equally likely in both directions, and neither direction is stable. Any position sooner or later loses stability and passes the baton to the opposite one. The transitions occur quickly, over about 5 thousand years, while the periods between them are a hundred times longer.

Most planets have magnetic fields, and this fact is even more difficult to explain than the earth's field. We still have a lot to learn about planetary magnetism.

Alfred Wegener

One of the most impressive properties of our planet was discovered in 1912, but was not taken into account until the 60s. The most convincing evidence in its favor was precisely the change of magnetic poles. We are talking about the fact that the earth's continents do not stand still, but slowly drift on the surface of the planet. According to the German scientist Alfred Wegener, who first published his theory, the current separate continents used to be one supercontinent, which he called Pangea(i.e. "All the earth"). It existed about 300 million years ago.

Surely Wegener was not the first to think of this. His idea, at least in part, arose under the influence of the amazing similarity of the outlines of the coasts of Africa and South America. On the map, this is especially evident. Naturally, Wegener relied on other data as well. He was not a geologist, but a meteorologist, a specialist in ancient climate, and he was surprised that in regions with a cold climate, rocks are found that clearly arose in regions with a warm one, and vice versa. For example, in the Sahara you can still find the remains of ancient glaciers, which are 420 million years old, and in Antarctica - petrified ferns. In those days, anyone would have told him that the climate had simply changed. However, Wegener was convinced that the climate remained practically the same, with the exception of the ice age, but that the continents themselves had changed, that is, moved. He assumed that they separated as a result of convection in the earth's mantle, but he was not sure.

This idea was considered insane, especially since it was not proposed by a geologist, and besides, Wegener ignored all the facts that did not fit into his theory. And the fact that the similarities between Africa and South America are not so perfect, and that the drift of the continents could not be explained. Convection obviously has nothing to do with it, since it is too weak. Great A'Tuin(suspects that A'Tuin is a girl), he may carry the whole world on his back, but he is just a fiction, and in the real world, it seems that such forces are simply unthinkable.

The word "unthinkable" we used not by chance. Many brilliant and respected scientists often repeat the same mistake. They confuse the expression "I don't understand how this can be" with "It's completely impossible." One of those, ashamed to admit one of us two, was a mathematician, and an excellent one, but when his calculations showed that the earth's mantle could not move the continents, it did not even occur to him that the theories on which the calculations were based were erroneous. His name was Sir Harold Jeffreys, and his problem was that he obviously lacked a flight of fancy, because not only did the outlines of the continents on both sides of the Atlantic coincide. From the point of view of geology and paleontology, too, everything converged. Take, for example, the petrified remains of a beast named mesosaurus, who lived 270 million years ago simultaneously in South America and Africa. It is unlikely that the mesosaurus swam across the Atlantic Ocean; rather, he simply lived on Pangea, having managed to settle on both continents when they were not yet separated.

However, in the 60s of the twentieth century, Wegener's idea was recognized, and his theory of "continental drift" was established in science. At a meeting of leading geologists, a young man named Edward Ballard, who closely resembled Pondering Toops, and two of his colleagues demonstrated the capabilities of the then new device called a computer. They instructed the machine to find the best match not only between Africa and South America, but also North America and Europe, given possible, but small changes. Instead of taking the current coastline, which was not a very bright idea from the beginning, allowing drift opponents to argue that the continents did not coincide, the young scientists used a contour corresponding to a depth of 3200 feet (1000 m) below sea level, because, according to in their opinion, it was less eroded. The contours fit well and the geology is just so great. And although the people at the conference still did not come to a consensus, the theory of continental drift finally received some recognition.

Today we have much more evidence and a clear understanding of the drift mechanism. In the central part of the Atlantic Ocean, halfway between South America and Africa, one of the mid-ocean ridges stretches from south to north (there are such, by the way, in all other oceans). Volcanic materials rise from the bowels along the entire ridge, and then spread along its slopes. And this has been happening for 200 million years. You can even send a submarine and just watch the process. Of course, the whole human life is not long enough to notice this, but America is moving away from Africa at a rate of 3/4 inch (2 cm) per year. Our nails grow at about the same rate, however, modern equipment is able to register these changes.

The most striking evidence of continental drift comes from the Earth's magnetic field: the rocks on both sides of the ranges have a curious pattern of magnetic stripes that reverse polarity from north to south and back, with the pattern on both slopes symmetrical. This means that the strips were frozen in the magnetic field as they cooled. When from time to time the earth's dynamo changed its polarity, the rocks of the ridge became magnetized in its field. Then, after the separation of the magnetized rocks, the same patterns appeared on opposite sides of the ridge.

The surface of the Earth is not a solid sphere. Both the continents and the ocean floor float on huge, especially hard plates that can move apart when magma seeps between them. (More often than not, this is due to convection in the mantle. It's just that Jeffreys didn't know everything we know about mantle movement.) There are about a dozen plates, ranging in width from six hundred (1,000 km) to six thousand (10,000 km) miles, and they keep turning. Where their boundaries touch, rub and slide, earthquakes and volcanic eruptions are constantly occurring. Especially in the Pacific Fire Belt, which stretches along the entire perimeter of the Pacific Ocean and includes the western coast of Chile, Central America, the USA and beyond the Japanese Islands and New Zealand. All of them are on the edge of one giant plate. Where plates collide, mountains arise: one plate is under another and lifts it, crushing and crushing its edge. India is not part of the Asian continent at all, it just crashed into it, creating the highest mountains in the world - the Himalayas. She accelerated so much that she still continues her movement, and the Himalayas are growing.

(c) Discworld Science, Terry Pratchett, Jack Cohen, Ian Stewart(Actually, read this book, you won’t find a better entertaining aid (but before that, in principle, read Pratchett’s “Flat World” series in bibliographic NOT AS POPULAR order)).

Video of the Magnetic field from Roskosmos:

How the compass works

Who hasn't seen a compass? A small thing that looks like a clock with one hand. You twist it, turn it, and the arrow stubbornly turns in one direction. The compass needle is a magnet that rotates freely on the needle. The principle of operation of a magnetic compass is based on the attraction-repulsion of two magnets. Opposite poles of magnets attract, like poles repel. Our planet is also such a magnet. Its strength is not great, it is not enough to manifest itself on a heavy magnet. However, a light compass needle, balanced on a needle, also turns under the influence of a small magnetic field.

sports compass

So that the compass needle does not hang out, but clearly shows the direction, regardless of the shaking, it must be sufficiently strongly magnetized. In sports compasses, a flask with an arrow is filled with liquid. Non-aggressive for plastic and metal parts, does not freeze in winter temperatures. The air bubble left in the flask carries the functions of a level indicator to orient the compass in a horizontal plane.

The primacy in the study of the Earth's magnetic field belongs to the English scientist William Gilbert. In his book "On the Magnet, Magnetic Bodies, and the Great Magnet - the Earth", published in 1600, he presented the Earth as a giant permanent magnet, the axis of which does not coincide with the axis of rotation of the Earth. The angle between the rotation axis and the magnetic axis is called the magnetic declination.

As a result of this discrepancy, it is not entirely correct to say that the compass needle always points to the north. It points to a point located at a distance of 2100 km from the North Pole, on Somerset Island (its coordinates are 75 °.6 N, 101 ° W - data for 1965). The Earth's magnetic poles drift slowly. In addition to such an error in the direction of the arrow (we will call it systematic), one should also not forget about other reasons for the compass to work incorrectly:

Metal objects or magnets near the compass will deflect the needle.
Electronic devices that are sources of electromagnetic fields
Deposits of minerals - metal ores
Magnetic storms that occur during years of strong solar activity distort the Earth's magnetic field.

And now, try to answer the questions for the savvy:

In the meantime, I'll give you some interesting facts about the Earth's magnetic field.

It turns out that it weakens by about 0.5% every 10 years. According to various estimates, it will disappear in 1-2 thousand years. It is assumed that at this moment there will be a polarity reversal of the magnet - the Earth. After that, the field will begin to grow again, but the north and south magnetic poles will change places. It is believed that this has happened to our planet a huge number of times.

It turns out that migratory birds also navigate “by compass”, more precisely, the Earth’s magnetic field serves as a guide for them. Recently, scientists have learned that birds have a small magnetic “compass” in the eye area - a tiny tissue field in which magnetite crystals are located, which have the ability to be magnetized in a magnetic field.

The simplest compass can be made independently. To do this, leave a sewing needle next to the magnet for several days. After that, the needle will be magnetized. After moistening it with fat or oil, gently lower the needle onto the surface of the water poured into the cup. Fat will not let her drown, and the needle will turn from north to south (well, or vice versa :).

Impressed? Now, you can check your answers to the questions:

Where do you think the compass needle would point if you were between the geographic north pole and the magnetic north pole?
- The northern end of the arrow will point .. to the south, and the southern end - to the north!
Where does the arrow point when the compass is in the region of the magnetic pole?
- it turns out that an arrow suspended on a thread in the region of the magnetic pole tends to turn around ... down, along the magnetic lines of the Earth!
If, guided by a compass, for a very long time to go all the time strictly to the northeast, then where will you come?
- you will come to the north magnetic pole! Try to trace your path on the globe, it turns out a very interesting route.

and this could look like a marine compass on the ship Columbus

We hope you enjoyed this article. If yes, then we will make more of these different ones!

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The 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 effect of the solar wind increases: from the side of the Sun, the geomagnetic field is compressed, and from the opposite, night side, it is pulled into a long "tail".

plasmasphere

A noticeable effect on the magnetic field on the Earth's surface is exerted by currents in the ionosphere. This is a 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 of magnetic storms on Earth with solar flares.

Field Options

The points of 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 circumference of a great circle in a plane that is perpendicular to the magnetic axis is called the magnetic equator. The magnetic field vector at the 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 the ripples extends from millihertz to one kilohertz.

magnetic meridian

Magnetic meridians are the projections of the lines of force of the Earth's magnetic field on 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 relates the emergence of the Earth's magnetic field to the flow of currents in a 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 of the Earth's radius. A similar mechanism of field generation can also take place on other planets, in particular, in the cores of Jupiter and Saturn (according to some assumptions, they consist of liquid metallic hydrogen).

Changes in the Earth's magnetic field

This is also confirmed by the current increase in the opening angle of the cusps (polar slots in the magnetosphere in the north and south), which reached 45° by the mid-1990s. The radiation material of the solar wind, interplanetary space and cosmic rays rushed into the widened gaps, as a result of which a greater amount of matter and energy enters the polar regions, which can lead to additional heating of the polar caps.

Geomagnetic coordinates (McIlwain coordinates)

In the physics of cosmic rays, specific coordinates in the geomagnetic field are widely used, 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 McIlwain parameter (eng. L-shell, L-value, McIlwain L-parameter ), B is the magnetic field induction (usually in G). The value L is usually taken as the parameter of the magnetic shell, 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. .

Research history

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

In 1544, German scientist Georg Hartmann discovered magnetic inclination. Magnetic inclination is the angle at which the arrow under the influence of the Earth's magnetic field deviates from the horizontal plane up or down. 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.

For the first time, the assumption about the presence of the Earth's magnetic field, which causes such a behavior of magnetized objects, was made by the English physician and natural philosopher William Gilbert (Eng. 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. The observations of the English astronomer Henry Gellibrand Henry Gellibrand) showed that the geomagnetic field is not constant, but changes slowly.

The angle at 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 undergoes changes with changes in geographic coordinates. The discovery of Columbus served as an impetus for a new study of the Earth's magnetic field: sailors needed information about it. The Russian scientist M. V. Lomonosov in 1759, in his report “Discourse on the Great Accuracy of the Sea Route,” gave valuable advice to increase the accuracy of the compass readings. To study terrestrial magnetism, M. V. Lomonosov recommended organizing a network of permanent points (observatories) in which to make systematic magnetic observations; such observations should be widely carried out at sea as well. 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 area 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 its main part comes out of the Earth, and the cause of small, short deviations in its values must be sought in the external environment.

Notes

Literature

Sivukhin D.V. General course of physics. - Ed. 4th, stereotypical. - M .: Fizmatlit; MIPT Publishing House, 2004. - Vol. III. Electricity. - 656 p. - ISBN 5-9221-0227-3; ISBN 5-89155-086-5.
Koshkin N.I., Shirkevich M.G. Handbook of elementary physics. - M .: Nauka, 1976.
N. V. Koronovsky The magnetic field of the geological past of the Earth. 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 related information

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

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See what the "Magnetic field of the Earth" is in other dictionaries:

To distance? 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 of 3R, the magnetic field ... ... Big Encyclopedic Dictionary

The space around the globe in which the power of terrestrial magnetism is found. The Earth's magnetic field is characterized by a strength vector, magnetic inclination and magnetic declination. Edwart. Explanatory Naval Dictionary, 2010 ... Marine Dictionary

earth's magnetic field- — [Ya.N. Luginsky, M.S. Fezi Zhilinskaya, Yu.S. Kabirov. English Russian Dictionary of Electrical Engineering and Power Engineering, Moscow, 1999] Electrical engineering topics, basic concepts EN Earth s magnetic field ... Technical Translator's Handbook

Reference

Gauss (Russian designation Gs, international - G) is a unit of measurement of magnetic induction in the CGS system. It is named after the German physicist and mathematician Carl Friedrich Gauss.

1 Gs = 100 μT;

1 T = 104 Gs.

It can be expressed in terms of the basic units of the CGS system as follows: 1 Gs = 1 g 1/2 .cm −1/2 .s −1 .

Experience

Source: physics textbooks on magnetism, Berkeley course.

Subject: m magnetic fields in matter.

Target: find out how different substances react to a magnetic field.

Imagine some experiments with a very strong field. Suppose we have made a solenoid with an inner diameter of 10 cm and a length of 40 cm.

1. The design of the coil that creates a strong magnetic field. The cross section of the winding through which the cooling water flows is shown. 2. The curve of the magnitude of the field B 2 on the axis of the coil.

Its outer diameter is 40 cm and most of the space is filled with copper winding. Such a coil will provide a constant field of 30,000 gs in the center, if you bring 400 to it kW electrical power and supply water for about 120 l per minute for heat dissipation.

These particular data are given to show that although the instrument is nothing out of the ordinary, it is still a fairly respectable laboratory magnet.

The magnitude of the field at the center of the magnet is about 105 times greater than the earth's magnetic field, and probably 5 or 10 times stronger than the field near any magnetic iron rod or horseshoe magnet!

Near the center of the solenoid, the field is fairly uniform and decreases by about half on the axis near the ends of the coil.

conclusions

So, as experiments show, in such magnets, the magnitude of the field (that is, induction or intensity) both inside the magnet and outside is almost five orders of magnitude greater than the magnitude of the Earth's field.

Also, only twice - not "at times!" - it is smaller outside the magnet.

And at the same time, 5-10 times the strength of an ordinary permanent magnet.

The average field strength of the earth on the surface is about 0.5 Oe (5.10 -5 T)

However, already a few hundred meters (if not tens) from such a magnet, the magnetic needle of the compass does not respond to either turning on or turning off the current.

At the same time, it responds well to the field of the earth or its anomalies at the slightest change in position. What does it say?

First of all, about the obviously underestimated figure of the induction of the earth's magnetic field - that is, not the induction itself, but how we measure it.

We measure the reaction of the loop with current, the angle of its rotation in the earth's magnetic field.

Any magnetometer is built on the principle of measuring not directly, but indirectly:

Only by the nature of the change in the value of tension;

Only on the surface of the earth, near it in the atmosphere and in near space.

We do not know the source of the field with a specific maximum. We measure only the difference in field strength at different points, and the strength gradient does not change too much with height. No mathematical calculations with the definition of the maximum when using the classical approach do not work here.

The influence of the magnetic field - experiments

It is known that even strong magnetic fields have practically no effect on chemical and biochemical processes. You can put your hand (no watch!) in the solenoid with a field of 30 kgf without any noticeable effects. It is difficult to say which class of substances your hand belongs to - paramagnetic or diamagnetic, but the force acting on it will, in any case, be no more than a few grams. Entire generations of mice have been bred and raised in strong magnetic fields that have had no noticeable effect on them. Other biological experiments also did not reveal any noteworthy magnetic effects on biological processes.

Important to remember!

It would be wrong to assume that weak effects always pass without consequences. Such reasoning might lead to the conclusion that gravity has no energetic significance on the molecular scale, but trees on a hillside grow vertically nonetheless. The explanation, apparently, lies in the total force acting on a biological object, the dimensions of which are much larger than the dimensions of the molecule. Indeed, a similar phenomenon ("tropism") has been experimentally demonstrated in the case of seedlings growing in the presence of a very non-uniform magnetic field.

Incidentally, if you place your head in a strong magnetic field and shake it, you will "taste" an electrolytic current in your mouth, which is proof of the presence of an induced electromotive force.

When interacting with matter, the roles of magnetic and electric fields are different. Because atoms and molecules are composed of slowly moving electrical charges, electrical forces in molecular processes dominate over magnetic ones.

conclusions

The impact of the magnetic field of such a magnet on biological objects is nothing more than a mosquito bite. Any living being or plant is constantly under the influence of much stronger terrestrial magnetism.

Therefore, the effect of an incorrectly measured field is not noticeable.

Calculations

1 gauss = 1 10 -4 tesla.

The SI unit of geomagnetic field strength (T) is ampere per meter (A/m). In magnetic exploration, another unit of Oersted (E) or gamma (G), equal to 10 -5 Oe, was also used. However, the practically measured parameter of the magnetic field is magnetic induction (or magnetic flux density). The unit of magnetic induction in the C system is the tesla (T). In magnetic exploration, a smaller unit of nanotesla (nT) is used, equal to 10 -9 T. Since for most media in which the magnetic field is studied (air, water, the vast majority of non-magnetic sedimentary rocks), the Earth's magnetic field can be quantitatively measured either in units of magnetic induction (in nT) or in the corresponding field strength - gamma.

The figure shows the total intensity of the Earth's magnetic field for the epoch of 1980. Isolines T are drawn through 4 μT (from P. Sharma's book "Geophysical methods in regional geology").

Thus

At the poles, the vertical components of the magnetic induction are approximately equal to 60 μT, and the horizontal components are zero. At the equator, the horizontal component is approximately 30 µT and the vertical component is zero.

It is in this way that the modern science of geomagnetism has long abandoned the basic principle of magnetism, two magnets placed flat against each other tend to connect with opposite poles.

That is, judging by the last phrase at the equator, there is no force (vertical component) that attracts a magnet to the earth! How repulsive!

Do these two magnets attract each other? That is, there is no attraction force, but there is a stretching force? Nonsense!

But at the poles with this arrangement of the magnet, it is, but the horizontal force disappears.

Moreover, the difference is only 2 times between these components!

We simply take two magnets and make sure that in a similar position, the magnet first unfolds and then attracts. SOUTH POLE to NORTH POLE!