What are the theories of terrestrial magnetism. Terrestrial magnetism and its elements
Our Earth- the fifth largest among the nine planets circling in their orbits around the Sun, the nearest star. Every second, the Earth travels about 30 km, and it makes a complete revolution around the Sun during the year. In addition, the Earth rotates on its axis like a top, making a complete revolution in 24 hours. The earth is not a perfect sphere. Its diameter is 12756 km at the equator (a conditional line dividing the globe into the northern and southern hemispheres) and 12714 km at the poles. The circumference of the earth at the equator is 40075 km.
Moon- Earth's closest space neighbor. Its diameter is about four times less than the diameter of the Earth and is equal to 3475 km. The rocks that make up the moon are less dense than those of the earth, so the moon weighs 8 times less than the earth.
Earth is the third planet from the Sun, consisting mainly of stony rocks.
"Questionnaire" of our planet, or what we firmly know about the Earth
Today we firmly know about the planet on which humanity lives, that its average radius is 6371 km. However, in the plane of the equator, it is slightly larger - about 6378 km, and the distance from the center of the Earth to the pole is less, almost 6357 km.
The surface of the Earth is 510 million km2, of which 71% is ocean, and the rest is land. Perhaps, in general, it would be more correct to call our planet the Ocean, since there is much less land on Earth?
The volume of the globe is indicated by the number of cubic kilometers that ends in twelve zeros. Each cubic meter of the material that makes up the Earth weighs a little more than 5.5 tons on average. So, if some giant managed to place the planet on gigantic scales, it would “pull” six and twenty-one zero tons!
The internal composition of the planet is dominated by iron - almost 35% of it; then comes oxygen (about 30%), then silicon (15%) and magnesium (12%). But this is on average.
Over the 4.6 billion years of the Earth's existence, gravity has pulled heavier rocks deeper into the earth, and left lighter ones closer to the surface. This "sorting" was also helped by the heat of the earth's interior - in the very middle of the Earth, the temperature is from 5000 to 6000 ° C. Therefore, the body of the planet became heterogeneous both in physical properties and in chemical composition. In the core is the core of the planet; it is surrounded by a mantle, and on top of everything is the earth's crust.
The planet Earth has its own magnetism - it is surrounded by an invisible field of magnetic forces that we do not feel, but it acts on materials containing iron or some other metals. You can detect the magnetic field using a compass. The compass needle is a long thin magnet. Interacting with earth's magnetism, it turns and points north and south.
1. Magnetic field lines, 2. Earth
It is most pronounced at the North and South magnetic poles. There, the magnetic lines of force are directed vertically.
Probably, the Earth's magnetic field is due to forces generated by its outer core - an iron shell, which is located at a depth of about 2900 km below the surface. The pressure at such a depth is very high, and the temperature exceeds 4000 °C. At this temperature, iron is in liquid state. Due to the rotation of the Earth, the streams of molten iron spin like a corkscrew, their movement generates electricity, and this, in turn, creates a magnetic field that surrounds the globe and protects us from radiation from high-energy particles that the Sun bombards the Earth with. However, some particles are attracted by the magnetic poles, causing flashes in the night sky - the aurora.
The magnetic field propagates into outer space and forms the magnetosphere. High-energy solar particles, the "solar wind", bombard the magnetosphere and cause it to take on a teardrop shape.
Enormous flows of thermal energy inside the Earth and the rotation of the planet around its axis make semi-liquid boulders move in spirals. These spiral currents excite electric currents that generate a magnetic field.
TERRESTRIAL MAGNETISM, a department of geophysics that studies the earth's magnetic field. Let the tension magnetic field at this point is represented by the vector F (Fig. 1). The vertical plane containing this vector is called the magnetic meridian plane. The angle D between the planes of the geographic and magnetic meridians is called declination. There are eastern and western declinations. It is customary to mark eastern declensions with a plus sign, western ones with a minus sign. The angle I formed by the vector F with the horizon plane is called inclination. The projection H of the vector F onto the horizontal plane is called the horizontal component, and the projection Z onto the vertical line is denoted by the term vertical component.
At present, the main instruments for measuring the elements of terrestrial magnetism are the magnetic theodolite and various systems of inclinators. The purpose of the magnetic theodolite is to measure the horizontal component of the magnetic field and declination. A horizontally located magnet, which can rotate about a vertical axis, is installed under the influence of the earth's magnetic field with its axis in the plane of the magnetic meridian. If it is taken out of this equilibrium position and then left to itself, then it will begin to oscillate around the plane of the magnetic meridian with a period T, determined by the formula:
where K is the moment of inertia of the oscillating system (magnet and frame) and M is the magnetic moment of the magnet. Having determined the value of K from special observations, it is possible to find the value of the product MH from the observed period T. Then a magnet is placed, the oscillation period of which is determined, at some distance from another, auxiliary magnet, which also has the ability to rotate about the vertical axis, and the first magnet is oriented so that the center of the second magnet is on the continuation of the magnetic axis of the first. In this case, in addition to H, the auxiliary magnet will also be affected by the field of the magnet M, which can be. found by formula:
where B is the distance between the centers of both magnets, a, b, ... are some constants. The magnet will leave the plane of the magnetic meridian and become in the direction of the resultant of these two forces. Without changing the relative arrangement of the parts of the installation, they find such a position of the deflecting magnet, in which the named resultant will be perpendicular to it (Fig. 2). By measuring the deflection angle v for this case, it is possible to find the value of the ratio from the relation sin v = f / H. From the obtained values of MH and H / M determine the horizontal component H. In the theory of terrestrial magnetism, the unit denoted by the symbol γ, equal to 0.00001 gauss, is widespread. A magnetic theodolite can be used as a declinator, a device for measuring declination. Combining the sighting plane with the direction of the magnetic axis of the magnet suspended on the thread, bring it into coincidence with the plane of the magnetic meridian. To get a reading on the circle corresponding to pointing the sighting device to the geographical north, it is enough to point at any object whose true azimuth is known. The difference between the readings of the geographic and magnetic meridians gives the value of the declination.
An inclinator is a device for measuring I. Modern magnetometry has two types of devices for measuring inclination - pointer and induction inclinators. The first device has a magnetic needle rotating about a horizontal axis placed in the center of the vertical limb. The plane of movement of the arrow is combined with the plane of the magnetic meridian; in this case, under ideal conditions, the magnetic axis of the arrow in the equilibrium position will coincide with the direction of the magnetic voltage at this point, and the angle between the direction of the magnetic axis of the arrow and the horizontal line will give the value I. The design of the induction inclinator is based on ( earth inductor) the phenomenon of induction in a conductor moving in a magnetic field is assumed. The essential feature of the device is the coil, which rotates about one of its diameters. When such a coil rotates in the earth's magnetic field, no EMF appears in it only if its axis of rotation coincides with the direction of the field. This position of the axis, marked by the absence of current in the galvanometer to which the coil is closed, is measured on a vertical circle. The angle between the direction of the axis of rotation of the coil and the horizon will be the angle of inclination.
The devices mentioned above are currently the most common. Special mention should be made of Ogloblinsky's magnetic theodolite, which determines the H/M value by the method of H compensation by the magnet field, for which the oscillation period is determined.
AT recent times the so-called. electrical methods for measuring H, in which deviations are made not with the help of a deflecting magnet, but with the help of the magnetic field of the coils. To achieve the accuracy required from magnetic measurements (0.2-0.02% of full voltage), the operating current is compared with the current from normal cells (potentiometer compensation).
Measurements made at various points on the earth's surface show that the magnetic field varies from point to point. In these changes, one can notice some regularities, the nature of which is best understood from an examination of the so-called. magnetic cards (Fig. 3 and 4).
If lines are plotted on a topographic basis connecting points of equal values of any element of terrestrial magnetism, then such a map will present a clear picture of the distribution of this element on the ground. According to the various elements of terrestrial magnetism, there are maps with various systems isolines. These isolines have special names depending on what element they depict. So, lines connecting points of equal declinations are called isogons (the line of zero declinations is called the agonic line), lines of equal inclinations are isoclines and lines of equal stresses are isodynes. There are isodynamics of the horizontal, vertical components, etc. If you build such maps for the entire surface of the globe, then you can notice the following features on them. In the equatorial regions, the greatest values of the horizontal force are observed (up to 0.39 gauss); the horizontal component decreases towards the poles. The opposite nature of the changes takes place for the vertical component. The line of zero values of the vertical component is called magnetic equator. Points with zero horizontal force are called magnetic poles earth. They do not coincide with geographic ones and have coordinates: the north magnetic pole is 70.5 ° N. sh. and 96.0°W D. (1922), south magnetic pole - 71.2 ° S. sh. and 151.0° E. D. (1912). All isogons intersect at the earth's magnetic poles.
A detailed study of the earth's magnetic field reveals that the isolines are far from being as smooth as the general picture suggests. On each such curve there are curvatures that disturb its smooth course. In some areas, these curvatures reach such large values that it is necessary to separate this area magnetically from the overall picture. Such regions are called anomalous, and in them one can observe values of magnetic elements that are many times greater than the normal field. Study magnetic anomalies clarified their close relationship with the geological structure of the upper parts of the earth's crust, Ch. arr. in relation to the content of magnetic minerals in them, and gave rise to a special branch of magnetometry, which has applied significance and sets as its task the application of magnetometry, measurements to mining exploration. Such anomalous regions, already of great industrial importance, are located in the Urals, in the Kursk district, in Krivoy Rog, in Sweden, in Finland, and in other places. To study the magnetic field of such regions, special equipment has been developed (the Tyberg-Thalen magnetometer, local calvariometers, etc.), which makes it possible to quickly obtain desired results measurements. The study of the earth's magnetic field at any one point reveals the fact of changes in this field over time. A detailed study of these temporal variations of the elements of terrestrial magnetism led to the establishment of their connection with the life of the globe as a whole. Variations reflect the rotation of the earth about its axis, the movement of the earth in relation to the sun, and a number of other phenomena of a cosmic order. The study of variations is carried out by special magnetic observatories equipped, in addition to precise instruments for measuring the elements of the earth's magnetic field, with special installations for continuous recording of temporal changes in magnetic elements. Such devices are called variometers, or magnetographs, and usually serve to record variations D, H and Z. A device for recording declination variations (variometer D, or unifilar) has a magnet with a mirror attached to it, freely hanging on a thin thread. Variations in declination, consisting in rotations of the plane of the magnetic meridian, cause the magnet suspended in this way to rotate. A beam thrown from a special illuminator, reflected from a magnet mirror, gives a moving light spot, which leaves a trace in the form of a curve on photosensitive paper, screwed onto a rotating drum or descending vertically. The line drawn by a ray reflected from a fixed mirror and the time marks make it possible to find the change in D for any moment of time from the obtained magnetogram. If you twist the thread, rotating the upper point of its attachment, then the magnet will leave the plane of the magnetic meridian; by proper twisting, you can put it in a position perpendicular to the original. In the new equilibrium position, on the one hand, H will act on the magnet, and on the other, the moment of the twisted thread. Any change in the horizontal component will cause a change in the equilibrium position of the magnet, and such a device will note variations in the horizontal component (variometer H, or bifilar, if the magnet is suspended on two parallel threads). These variations are recorded in the same way as declination changes are recorded. Finally, the third device, which serves to record variations in the vertical component (Lloyd's scales, variometer Z), has a magnet oscillating, like a balance beam, about a horizontal axis. By properly moving the center of gravity with the help of a movable weight, the magnet of this device is brought into a position close to horizontal, and usually set so that the plane of movement of the magnet is directed perpendicular to the plane of the magnetic meridian. In this case, the equilibrium position of the magnet is determined by the action of Z and the weight of the system. A change in the first value will cause some tilt of the magnet proportional to the change in the vertical component. These tilt changes are recorded, like the previous one, by photographic means and provide material for judgments about the variations in the vertical component.
If we subject the curves recorded by magnetographs (magnetograms) to analysis, we can find a whole series of features on them, of which, first of all, a clearly pronounced diurnal variation will catch the eye. The position of the maxima and minima of the diurnal variation, as well as their values, change from day to day within small limits, and therefore, to characterize the diurnal variation, some average curves are drawn up over a certain time interval. In FIG. Figure 5 shows the curves of changes in D, H, and Z for the observatory in Slutsk in September 1927, in which the diurnal variations of the elements are clearly visible.
The most illustrative way of depicting variations is the so-called. vector diagram, representing the movement of the end of the vector F over time. Two projections of the vector diagram on the yz and xy planes are given in Fig. 6. From this FIG. It can be seen how the time of the year affects the nature of the daily course: in the winter months, the fluctuations of magnetic elements are much less than in the summer.
In addition to variations due to the diurnal variation, magnetograms sometimes show sharp changes, often reaching very large values. Such abrupt changes in the magnetic elements are accompanied by a number of other phenomena, such as auroras in the arctic regions, the appearance of induced currents in telegraph and telephone lines, etc., and are called magnetic storms. There is a fundamental difference between variations due to the normal course and variations due to storms. While normal changes occur for each observation point in local time, variations caused by storms occur simultaneously for the entire globe. This circumstance points to the different nature of the variations of both types.
The desire to explain the distribution of elements of terrestrial magnetism observed on the ground surface led Gauss to construct a mathematical theory of geomagnetism. The study of the elements of terrestrial magnetism since the first geomagnetic measurements revealed the existence of the so-called. the secular course of the elements, and further development Gaussian theory included, among other things, taking into account these secular variations. As a result of the work of Peterson, Neumeier, and other investigators, there is now a formula for the potential that also takes into account this secular variation.
Among the hypotheses proposed to explain the daily and annual variation of geomagnetic elements, one should note the hypothesis proposed by Balfour-Stewart and developed by Schuster. According to these researchers, in the high electrically conductive layers of the atmosphere, under the thermal action of the sun's rays, movements of gas masses occur. The magnetic field of the earth in these moving conducting masses induces electric currents, the magnetic field of which manifests itself in the form of daily variations. This theory explains well the decrease in the amplitude of variations in the winter months and elucidates the prevailing role of local time. As for magnetic storms, the next study showed their close connection with the activity of the sun. The elucidation of this connection led to the following generally recognized theory of magnetic perturbations at the present time. The sun, at the moments of its most intense activity, throws out streams of electrically charged particles (for example, electrons). Such a flow, falling into the upper layers of the atmosphere, ionizes it and creates the possibility of the flow of intense electric currents, the magnetic field of which is those perturbations that we call magnetic storms. Such an explanation of the nature of magnetic storms is in good agreement with the results of the theory of auroras developed by Shtermer.
Terrestrial magnetism geomagnetism, magnetic field of the Earth and near-Earth space; a branch of geophysics that studies the distribution in space and changes in time of the geomagnetic field, as well as the geophysical processes associated with it in the Earth and the upper atmosphere. At each point in space, the geomagnetic field is characterized by the intensity vector T, the magnitude and direction of which are determined by 3 components X, Y, Z(north, east and vertical) in a rectangular coordinate system ( rice. one
) or 3 earth elements: the horizontal component of the tension H, magnetic declination D (See. Magnetic declination) (the angle between H and the plane of the geographic meridian) and magnetic inclination I(angle between T and the horizon plane). The Earth's magnetism is due to the action of constant sources located within the Earth, which experience only slow secular changes (variations), and external (variable) sources located in the Earth's magnetosphere and the ionosphere. Accordingly, the main (main, Earth magnetism 99%) and variable (Earth magnetism 1%) geomagnetic fields are distinguished. Main (permanent) geomagnetic field. To study the spatial distribution of the main geomagnetic field, the values measured in different places H, D, I put on the maps (Magnetic maps) and connect the points of equal values of the elements with lines. Such lines are called isodynamics, isogones, and isoclines, respectively. Line (isoclinic) I= 0, i.e., the magnetic equator does not coincide with the geographic equator. With increasing latitude, the value I increases to 90° at the magnetic poles (See Magnetic Pole). Full tension T (rice. 2
) from the equator to the pole increases from 33.4 to 55.7 a/m(from 0.42 to 0.70 Oe). Coordinates of the north magnetic pole for 1970: longitude 101.5° W. D., latitude 75.7 ° N. sh.; south magnetic pole: longitude 140.3° E D., latitude 65.5 ° S. sh. A complex picture of the distribution of the geomagnetic field in the first approximation can be represented by the field of a dipole (See Dipole) (eccentric, with an offset from the center of the Earth by approximately 436 km) or a homogeneous magnetized sphere, the magnetic moment of which is directed at an angle of 11.5 ° to the axis of rotation of the Earth. Geomagnetic poles (poles of a uniformly magnetized ball) and magnetic poles define, respectively, a system of geomagnetic coordinates (geomagnetic latitude, geomagnetic meridian, geomagnetic equator) and magnetic coordinates (magnetic latitude, magnetic meridian). Deviations of the actual distribution of the geomagnetic field from the dipole (normal) are called magnetic anomalies (See Magnetic anomalies). Depending on the intensity and size of the occupied area, global anomalies of deep origin are distinguished, for example, East Siberian, Brazilian, etc., as well as regional and local anomalies. The latter can be caused, for example, by uneven distribution in earth's crust ferromagnetic minerals. The influence of world anomalies affects up to the heights Earth's magnetism 0.5 R3 above the surface of the earth ( R3- radius of the earth). The main geomagnetic field has a dipole character up to altitudes Earth's magnetism3 R3. It experiences secular variations, not the same for everything. the globe. In places of the most intense secular variation, the variations reach 150γ per year (1γ
= 10 -5 e). There is also a systematic westward drift of magnetic anomalies at a rate of about 0.2° per year and a change in the magnitude and direction of the Earth's magnetic moment at a rate of 20γ per year. Due to secular variations and insufficient knowledge of the geomagnetic field over large areas (oceans and polar regions), it becomes necessary to re-compile magnetic maps. For this purpose, global magnetic surveys are carried out on land, in the oceans (on non-magnetic ships), in airspace(aeromagnetic survey) and in outer space (using artificial satellites Earth). For measurements, they use: Magnetic compass, Magnetic theodolite, magnetic scales, inclinator, magnetometer, aeromagnetometer and other devices. The study of Z. m. and the compilation of maps of all its elements plays important role for sea and air navigation, in geodesy, mine surveying. The study of the geomagnetic field of past eras is carried out according to the residual magnetization of rocks (see Paleomagnetism), and for the historical period - according to the magnetization of baked clay products (bricks, ceramic dishes, etc.). Paleomagnetic studies show that the direction of the Earth's main magnetic field has repeatedly reversed in the past. The last such change took place about 0.7 million years ago. A. D. Shevnin.
Origin of the main geomagnetic field. To explain the origin of the main geomagnetic field, many different hypotheses have been put forward, including even hypotheses about the existence of a fundamental law of nature, according to which any rotating body has a magnetic moment. Attempts have been made to explain the main geomagnetic field by the presence of ferromagnetic materials in the Earth's crust or in its core; movement electric charges, which, participating in the daily rotation of the Earth, create an electric current; the presence in the Earth's core of currents caused by the thermoelectromotive force at the boundary between the core and the mantle, etc., and, finally, the action of the so-called hydromagnetic dynamo in the liquid metal core of the Earth. Modern data on secular variations and multiple changes in the polarity of the geomagnetic field are satisfactorily explained only by the hypothesis of a hydromagnetic dynamo (HD). According to this hypothesis, fairly complex and intense movements can occur in the electrically conductive liquid core of the Earth, leading to self-excitation of the magnetic field, similar to how the current and magnetic field are generated in a self-excited dynamo. The action of the HD is based on electromagnetic induction in a moving medium, which, in its motion, crosses the lines of force of the magnetic field. Research into HD is based on magnetohydrodynamics (see Magnetohydrodynamics). If we assume that the velocity of matter in the liquid core of the Earth is given, then we can prove the fundamental possibility of generating a magnetic field during motions different kind, both stationary and non-stationary, regular and turbulent. The average magnetic field in the core can be represented as the sum of two components - the toroidal field ATφ and fields VR, whose lines of force lie in meridional planes ( rice. 3
). Field lines of a toroidal magnetic field ATφ are closed inside the earth's core and do not go outside. According to the most common terrestrial HD scheme, the field Bφ is hundreds of times stronger than the field penetrating out of the nucleus In r, which has a predominantly dipole form. The inhomogeneous rotation of the electrically conductive fluid in the Earth's core deforms the field lines In r and forms field lines from them AT(. In turn, the field In r is generated due to the inductive interaction of a conducting fluid moving in a complex way with the field ATφ. To ensure field generation In r from ATφ fluid motion should not be axisymmetric. As for the rest, as the kinetic theory of HD shows, motions can be very diverse. The movements of the conducting fluid are created in the process of generation, in addition to the field In r, as well as other slowly changing fields, which, penetrating outward from the core, cause secular variations in the main geomagnetic field. The general theory of HD, investigating both the generation of the field and the "engine" of the terrestrial HD, i.e., the origin of motions, is still at the initial stage of development, and much is still hypothetical in it. As causes of motions, the Archimedean forces, due to small density inhomogeneities in the nucleus, and the forces of inertia are put forward (See Force of inertia).
The former can be associated either with the release of heat in the core and thermal expansion of the liquid (thermal convection), or with the inhomogeneity of the composition of the core due to the release of impurities at its boundaries. The latter can be caused by acceleration due to precession (See Precession) earth's axis. The proximity of the geomagnetic field to the field of a dipole with an axis almost parallel to the axis of the Earth's rotation indicates a close relationship between the Earth's rotation and the origin of the Earth's m. Rotation creates a Coriolis force (See Coriolis force) ,
who can play essential role in the Earth's HD mechanism. The dependence of the magnitude of the geomagnetic field on the intensity of the movement of matter in the earth's core is complex and has not yet been studied enough. According to paleomagnetic studies, the magnitude of the geomagnetic field fluctuates, but on average, in order of magnitude, it remains unchanged for a long time - about hundreds of million years. The functioning of the Earth's HD is associated with many processes in the Earth's core and mantle; therefore, the study of the main geomagnetic field and the Earth's HD is an essential part of the entire complex of geophysical studies of the internal structure and development of the Earth. S. I. Braginsky.
Variable geomagnetic field. Measurements made on satellites and rockets have shown that the interaction of solar wind plasma with geomagnetic field leads to disruption of the dipole structure of the field from a distance Terrestrial magnetism3 Rz from the center of the earth. The solar wind localizes the geomagnetic field in a limited volume of near-Earth space - the Earth's magnetosphere, while at the boundary of the magnetosphere the dynamic pressure of the solar wind is balanced by the pressure of the Earth's magnetic field. The solar wind compresses the Earth's magnetic field from the day side and carries away the geomagnetic field lines of the polar regions to the night side, forming the Earth's magnetic tail near the ecliptic plane with a length of at least 5 million km. km(cm. rice.
in articles Earth and Earth's magnetosphere). The approximately dipole region of the field with closed lines of force (the inner magnetosphere) is a magnetic trap for charged particles of near-Earth plasma (see Radiation Belts of the Earth). The solar wind plasma flow around the magnetosphere with a variable density and velocity of charged particles, as well as the breakthrough of particles into the magnetosphere, lead to a change in the intensity of electric current systems in the Earth's magnetosphere and ionosphere. Current systems, in turn, cause geomagnetic field oscillations in near-Earth space and on the Earth's surface in a wide frequency range (from 10 -5 to 10 2 Hz) and amplitudes (from 10 -3 to 10 -7 uh).
Photographic recording of continuous changes in the geomagnetic field is carried out in magnetic observatories with the help of Magnetographs. During quiet times, periodic solar-diurnal and lunar-diurnal variations are observed at low and middle latitudes.
amplitudes 30-70γ and 1-5γ respectively. Other observed irregular field oscillations of various shapes and amplitudes are called magnetic disturbances, among which there are several types of magnetic variations. Magnetic disturbances covering the entire Earth and continuing from one ( rice. four
) up to several days are called global magnetic storms (See Magnetic storms) ,
during which the amplitude of the individual components may exceed 1000γ. A magnetic storm is one of the manifestations of strong disturbances in the magnetosphere that arise when the parameters of the solar wind change, especially the velocity of its particles and the normal component of the interplanetary magnetic field relative to the ecliptic plane. Strong perturbations of the magnetosphere are accompanied by the appearance of auroras, ionospheric disturbances, X-ray and low-frequency radiation in the Earth's upper atmosphere. Practical applications of the phenomena of Z. m. Under the action of the geomagnetic field, the magnetic needle is located in the plane of the magnetic meridian. This phenomenon has been used since ancient times for orientation on the ground, laying the course of ships on the high seas, in geodetic and mine surveying practice, in military affairs, etc. (see Compass, Bussol). The study of local magnetic anomalies makes it possible to detect minerals, primarily iron ore (see Magnetic exploration), and in combination with other geophysical exploration methods, to determine their location and reserves. The magnetotelluric method of sounding the interior of the Earth has become widespread, in which the electrical conductivity of the Earth's inner layers is calculated from the field of a magnetic storm and then the pressure and temperature existing there are estimated. One of the sources of information about the upper layers of the atmosphere is geomagnetic variations. Magnetic disturbances associated, for example, with a magnetic storm occur several hours earlier than under its influence, changes in the ionosphere occur that disrupt radio communications. This makes it possible to make the magnetic forecasts needed to ensure uninterrupted radio communications (radio weather forecasts). Geomagnetic data also serve to predict the radiation situation in near-Earth space during space flights. The constancy of the geomagnetic field up to heights of several Earth radii is used for orientation and maneuver of spacecraft. The geomagnetic field affects living organisms, vegetable world and a person. For example, during periods of magnetic storms, the number of cardiovascular diseases increases, the condition of patients suffering from hypertension worsens, and so on. Study of character electromagnetic influence on living organisms is one of the new and promising directions biology. A. D. Shevnin. Lit.: Yanovsky B. M., Terrestrial magnetism, vol. 1-2, L., 1963-64; his own, Development of work on geomagnetism in the USSR over the years Soviet power. "Izv. Academy of Sciences of the USSR, Physics of the Earth, 1967, no. 11, p. 54; Reference book on the alternating magnetic field of the USSR, L., 1954; Near-Earth outer space. Reference data, trans. from English, M., 1966; The Present and Past of the Earth's Magnetic Field, M., 1965; Braginsky S.I., On the foundations of the theory of the Earth's hydromagnetic dynamo, "Geomagnetism and Aeronomy", 1967, v.7, No. 3, p. 401; Solar-terrestrial physics, M., 1968. Rice. 2. Map of the total strength of the geomagnetic field (in oersteds) for the epoch 1965; black circles - magnetic poles(M.P.). The map shows the world magnetic anomalies: Brazilian (B.A.) and East Siberian (East-S.A.). Rice. 3. Scheme of magnetic fields in the Earth's hydromagnetic dynamo: NS - the axis of rotation of the Earth: В р - field close to the field of a dipole directed along the axis of rotation of the Earth; B φ - toroidal field (on the order of hundreds of gauss), closing inside the earth's core. Rice. 4. Magnetogram, which recorded a small magnetic storm: H 0 , D 0 , Z 0 - the origin of the corresponding component of terrestrial magnetism; the arrows show the direction of counting.
Big soviet encyclopedia. - M.: Soviet Encyclopedia. 1969-1978 .
See what "Earth magnetism" is in other dictionaries:
- (geomagnetism), 1) Earth's magnetic field. 2) A branch of geophysics that studies the distribution in the field and changes in time of the magnetic field. fields of the Earth, as well as related physical. processes in the Earth and in the atmosphere. At each point, right va geomagn. The field is characterized... Physical Encyclopedia
- (Terrestrial magnetism) a magnetic field near the earth, most easily detected by its effect on a magnetic needle. The direction of the Z. M. force is usually determined by two angles: magnetic declination and magnetic inclination, and the magnitude of the Z. M. force ... ... Marine Dictionary
Big Encyclopedic Dictionary
terrestrial magnetism- geomagnetism - [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 Synonyms geomagnetism EN Earth magnetismterrestrial ... ... Technical Translator's Handbook
terrestrial magnetism- Earth's magnetic field, considered as a whole, varying in intensity and direction, affecting the needle of a magnetic compass, which points to the north geomagnetic pole ... Geography Dictionary
TERRESTRIAL MAGNETISM- Earth's magnetic field. It is made up of two components: constant field conditioned internal structure Earth, and an alternating field due to the action of electric currents in the ionosphere and magnetosphere, not exceeding 1% of the constant ... ... Great Polytechnic Encyclopedia
The Earth's magnetic field, the existence of which is due to the action of constant sources located inside the Earth (see Hydromagnetic dynamo) and creating the main component of the field (99%), as well as variable sources (electric currents) in ... ... encyclopedic Dictionary
terrestrial magnetism- Žemės magnetizmas statusas T sritis fizika atitikmenys: engl. earth magnetism; geomagnetismus; terrestrial magnetism vok. Erdmagnetismus, m rus. geomagnetism, m; terrestrial magnetism, m pranc. geomagnetisme, m; magnétisme terrestre, m … Fizikos terminų žodynas
The principle of operation of a magnetic compass is based on the property of a magnetic needle to be set in the direction of the magnetic field strength vector in which it is located.
The earth and near-Earth space are surrounded by a magnetic field, the lines of force of which come out of the south magnetic pole, go around the globe and converge at the north magnetic pole. The magnetic poles of the Earth do not coincide with the geographic ones, their position in 1970 was determined approximately by the coordinates: North - φ = 75°N, λ = 99°W; Southern - φ = 66.5°S; λ = 140°E. It is generally accepted that positive magnetism is concentrated at the South magnetic pole, and negative magnetism is concentrated at the North.
The Earth's magnetic field characterizes the intensity vector T(total strength of terrestrial magnetism), which is directed tangentially to the magnetic lines of force (Fig. 9). In the general case, this vector makes some angle I with the plane true horizon and does not lie in the plane of the true meridian.
Rice. 9. Elements of terrestrial magnetism
The vertical plane passing through the vector of the Earth's magnetic field at a given point is called plane of the magnetic meridian. In this plane, the axis of a freely suspended magnetic needle is set. The trace from the intersection of the plane of the magnetic meridian with the plane of the true horizon is called magnetic meridian.
The angle in the plane of the true horizon between the true meridian (noon line N - S) and the magnetic meridian is called magnetic declination (d). The declination is measured from the northern part of the true meridian to E or W from 0 to 180°. The eastern (E) declination is assigned a (+) sign, and the western (W) declination is assigned a (-) sign.
The angle between the plane of the true horizon and the vector of the total force of terrestrial magnetism is called magnetic inclination(/). At the magnetic poles, the inclination is maximum and equal to 90°, and as the distance from the poles decreases to zero. A curve on the earth's surface formed by points at which the magnetic inclination is zero is called magnetic equator.
The vector of the Earth's magnetic field can be decomposed into a horizontal (H) and vertical (Z) components (see Fig. 9). Quantities T, H,Z and I related by the relations
Horizontal component H is directed along the magnetic meridian and holds in it the sensitive element (arrow, card) of the magnetic compass. As can be seen from (12), the maximum value H accepts at I - 0, i.e. at the magnetic equator, and becomes zero at the magnetic poles. Therefore, in near-polar regions, the readings of the magnetic compass are not reliable, and at the magnetic poles the compass does not work at all.
Quantities d, I, H, Z called elements of terrestrial magnetism. Of all the elements highest value for navigation has a magnetic declination. The distribution of magnetism on the earth's surface is shown on special maps of the elements of earth's magnetism. Curved lines on the map connect points with the same values of one or another element. A line connecting points with the same declination is called isogon. Zero declination isoline - agona separates areas with east and west declination. The magnitude of the magnetic declination is also given on nautical charts.
All elements of terrestrial magnetism are subject to changes in time - variations. Declension variations distinguish secular, daily and aperiodic.
Age change is the change in the mean annual declination from year to year. The annual change in declination (annual increase or decrease) does not exceed 15" and is shown on nautical charts. per diem or solar diurnal variations declinations have a period equal to a solar day, are insignificant in magnitude and are not taken into account in navigation. Aperiodic changes or magnetic wozindignation occur without certain period.
Magnetic disturbances of great intensity, when all elements of terrestrial magnetism change sharply within a few hours, are called magnetic storms. The occurrence of magnetic storms is associated with solar activity and observed throughout the earth's surface. Compass readings during magnetic storms are unreliable - the declination can vary by several tens of degrees.
In some areas of the Earth's surface, the magnitudes of the elements of magnetism, including declination, differ sharply from their values in the surrounding area. Such a change is associated with the accumulation of magnetic rocks under the surface and is called magnetic anomaly. Areas of magnetic anomalies and limits of declination change in them
Rice. 10. Magnetic directions
indicated on nautical charts and in sailing directions. An example of anomalies are magnetic anomalies in the Povenets Bay of Lake Onega and in the southern part of Lake Ladoga. It is difficult and sometimes even dangerous to use the readings of a magnetic compass in the region of anomalies.
For use in practice, data from the map on the magnitude of the declination must be adjusted to the year of navigation. For this purpose, the annual change in declination is multiplied by the number of years that have passed from the year to which the declination is related. The resulting correction corrects the declination taken from the map. Note that the term "annual decrease" or "annual increase" refers to the absolute value of the declination.
If navigation occurs between points for which the declination is indicated on the map, then the declination is interpolated by eye, dividing the navigation area into sections in which the declination is assumed to be constant.
Directions in the sea, determined relative to the magnetic meridian, are called magnetic (Fig. 10).
magnetic course(MK) - the angle in the plane of the true horizon between the northern part of the magnetic meridian and the diametrical plane of the vessel in the direction of its movement.
Magnetic bearing(MP) - the angle in the plane of the true horizon between the northern part of the magnetic meridian and the direction from the observation point to the object.
A direction that differs by 180° from the magnetic bearing is called reverse magnetic bearing(WMD). Magnetic courses and bearings are counted in a circular count from 0 to 360°.
Knowing the magnitude of the declination, you can go from magnetic directions to true and vice versa. From fig. 10 shows that the true and magnetic directions are related dependencies:
(13)
(14)
Formulas (13), (14) are algebraic, where the declination d can be positive or negative.
When the Earth rotates around its own axis, the liquid layer of the outer core allows the mantle and solid crust to rotate faster than the inner core. As a result, the electrons in the core move relative to the electrons in the mantle and crust. This movement of electrons forms a natural dynamo. It creates a magnetic field similar to the field inductors.
The Earth's magnetic axis is inclined at an angle of about 11° to its geographic axis. It continuously changes its angle of inclination, but so slowly that for several tens of thousands of years it almost retains its relative position.
The arrow on the compass deviates somewhat away from the geographic poles. The angle between the magnetic meridian and the geographic meridian varies from one region to another. Small deviations of the magnetic field are probably due to local vortex motions in the outer core, at the junction of the core and mantle. A similar effect can be caused by large bodies of magnetized rocks and ores in the earth's crust.
The geomagnetic field is affected solar wind- the flow of electrically charged particles emitted by the Sun. Getting into the outer atmosphere of the Earth, these particles cause small changes in its magnetic field near the earth's surface, which are systematic (like night and daytime) or irregular (like magnetic storms) in nature.
Earth's magnetic field in the past
Under the influence of the planet's magnetic field, the rocks were magnetized during formation, retaining this magnetization in the following epochs. This phenomenon is called paleomagnetism. When heated, rocks, like a permanent magnet, lose their magnetization. The cooled rocks are again magnetized by the earth's field. This natural remanence is oriented parallel to the lines of force of the geomagnetic field that existed at the time of rock formation. Therefore, the direction of the field that was in effect at the time of their solidification is forever imprinted in the rocks, which can be used to study geological history of the earth's magnetic field.
The technique of paleomagnetic research is to measure the natural residual magnetism in cylindrical columns drilled from the rock mass. The obtained paleomagnetic coordinates of the samples make it possible to determine the initial location of the rocks. Paleomagnetic coordinates, expressed in magnetic latitudes, are similar geographical latitudes(but only in relation to the magnetic pole) and refer to the position of the magnetic pole during the magnetization period of the rock. The data obtained as a result of such measurements indicate that for a long time the magnetic poles "wandered", changing their position. The wandering of the poles on the continents is fixed in different ways. But for a certain period of geological history, the polar directions established on different continents can be combined into one line if these continents are imagined in positions other than today. It was in this way that it was possible to establish and map continental drift path. The results obtained with this method are in fairly good agreement with other evidence. continental drift- seafloor spreading and data obtained from the study of rocks and fossils characterizing paleoclimatic conditions.
The polarity of the remanent magnetization (“fossil” magnetic field) of rocks formed in short periods of time turns out to be reversed. This fact is explained not by the rotation of the continent by 180° (this would take too much time), but change in the polarity of the geomagnetic field. Such a change in the direction of the earth's magnetic field is called reversal or inversion. Inversions mark the boundaries of periods of geological history during which the geomagnetic field maintained a constant polarity. These periods were of different duration. Age dating of reversals (by studying the decay of radioactive isotopes in rocks) made it possible to create a paleomagnetic scale of geological time. This scale can be used to determine the age of rocks by analyzing their remanence. Comparison of the paleomagnetic time scale with the "magnetic anomalies" of the seabed confirmed the spreading hypothesis.
Magnetic and electrical exploration
Many ore bodies and rocks rich in magnetic minerals create a strong local magnetic field. This property is used in geophysical prospecting and exploration of mineral deposits. With the help of sensitive instruments - magnetometers, industrially valuable accumulations of minerals are detected. There is also a method that uses natural electrical currents that occur between earth's surface and ore body due to seeping groundwater. The interaction of such currents with the geomagnetic field is measurable and serves as the basis for discovering deposits.