On the Earth's Magnetic Field

The origin of the Earth's magnetic field and its numerous peculiarities have still not received a sufficiently clear explanation, despite the rapid development of the technique of magnetic measurements. It is known that the magnetic axis of the Earth deviates from the geographic one, forming with it an angle equal to \(11.5^\circ\). Therefore at present it is customary to regard as the principal (normal) magnetic field of the Earth a dipole field, whose magnetic moment and axis make an angle of \(11.5^\circ\) with the axis of rotation of the Earth. The deviations of the actual magnetic field of the Earth from the dipole field are combined into the anomalous field of the Earth, explained by the influence of various factors less essential than those which create the principal field.

Even N. A. Umov \(^{1}\) and P. N. Lebedev \(^{2}\), in their works on the origin of terrestrial magnetism, pointed out that the main cause of the appearance of the Earth's magnetic field is the rotation of the Earth about its axis, and therefore the moment and the axis of the principal magnetic field of the Earth must coincide with the axis of its rotation. The comparatively small deviation of the magnetic axis from the axis of rotation, as well as the other peculiarities of the actual magnetic field of the Earth, may be caused by various secondary causes not connected with the Earth's rotation. The magnetic fields of stars, recently discovered, have received the same explanation \(^{3}\).

The magnetic field at various points of the terrestrial globe changes continuously with time; moreover, these changes occur so rapidly that they cannot be connected with any geological processes taking place in the interior of the Earth. The arrangement of the isolines of the geomagnetic field on the map of the Earth indicates the existence of a connection between the elements of this field and the shoreline separating the continents from the oceans and seas. To explain this connection it was suggested that under the continents there are enormous inhomogeneities of ferromagnetic masses. However, the depths of the oceans are so small in comparison with the radius of the Earth that this explanation has always seemed unconvincing.

Recently Academician V. V. Shuleikin proposed a new theory of the origin of the Earth's magnetic field, which in his opinion illuminates these facts and establishes a connection between them \(^{4}\). This theory is based on the discovery made in 1935 by A. T. Mironov of electric currents in the sea \(^{5}\). The density of these currents, measured in the surface layers of the water, proved to be of the order of \(1\ a\) per hectare of surface perpendicular to the direction of the vec-

of the electric-field intensity vector. It is connected with solar activity and increases sharply during magnetic storms. The nature of these currents is apparently analogous to the telluric currents long since discovered in the earth’s crust, but their density is incomparably greater owing to the high electrical conductivity of sea water. V. V. Shuleikin assumes that the Earth’s main magnetic field is created as a consequence of its rotation and that its axis coincides with the Earth’s axis of rotation. Electric currents circulating in the waters of the oceans and seas create an additional (anomalous) magnetic field. Combining with the main field, it displaces the Earth’s magnetic axis and creates the resulting field, the isolines of which are connected with the coastline of the continents. Changes in the intensity of the anomalous magnetic field cause changes in the entire magnetic field of the Earth.

To test this theory, a “magnetic globe”—a model of the globe with a diameter of 43 cm—was built by L. A. Korneeva, a collaborator of the Marine Hydrophysical Institute of the Academy of Sciences.^6 The seas and oceans were laid out on the surface of the globe from sheet copper, while the continents were made of a nonconducting material. To create in the oceans and seas currents producing an anomalous magnetic field, a direct-current source was connected along the equator between America and Africa. The normal field was created by a small solenoid placed at the center of the globe on the north-south axis. The magnitudes of both fields were specified in proportion to their actual values. The resulting magnetic field was measured with a miniature magnetic needle suspended on a silk thread 1.5 m long. Measures were taken to compensate for the influence of the horizontal component of the terrestrial magnetic field. The results of the measurements are in good qualitative agreement with the actual magnetic field of the Earth. In particular, the anomalous field causes a displacement of the magnetic poles relative to the geographic ones, a shift of the magnetic axis from the center of the Earth, and the appearance of regions of eastern and western declination. The isolines of the resulting field prove to be similar to the actual ones and are connected in the same way with the outlines of the continental coastline.

Korneeva’s experiments confirmed two basic assumptions of V. V. Shuleikin’s theory: the displacement of the magnetic axis and the connection with the coastline of the continents. A check of the temporal variations of the Earth’s magnetic field was not carried out because systematic measurements of the density of electric currents in the seas and oceans over the required period were lacking. For the same reason, and also because the density of currents in deep waters has not yet been measured by anyone, quantitative measurements could not be made. However, the experiments performed on the model nevertheless indicate that the magnitude of the anomalous magnetic field of the seas and oceans, even when deep currents are taken into account, will be insufficient for quantitative agreement with the actual one. Therefore it is necessary to find other sources of the anomalous magnetic field which would supplement the field of the seas and oceans and would be connected with their position on the Earth.

V. V. Shuleikin has pointed out still another possible source of the anomalous magnetic field of the Earth. In 1950 he showed^7 that thermal contradictions between oceans and continents exist also at great heights in the atmosphere, which at the same latitudes is always colder above the oceans than above the continents. Owing to this, cyclonic movements of air with enormous velocities constantly exist around the continents, the largest component of which is directed along the coastline. Under the influence of cosmic rays, many positively and negatively charged particles arise in the atmosphere. Negatively charged particles (for example, mesons), interacting with the substance of the atmosphere, produce processes leading to the further formation of new particles. Positively charged particles diffuse in the atmosphere in the form of charged gas and participate in the general circulation of air at different heights. Owing to this, convectional

currents in the atmosphere, whose direction is connected with the direction of the flows of air masses, i.e., is determined to a considerable degree by the outlines of the coastline. The additional magnetic field produced by them will add to the magnetic field of seas and oceans, increasing the anomalous magnetic field of the Earth. Since as yet there is not sufficiently reliable information about air currents at altitudes above 20 km and about the density of electric charges in these layers of the atmosphere, quantitative calculations of the intensity of the additional anomalous magnetic field cannot be made. However, the results obtained by S. N. Vernov with colleagues from measurements of the intensity of the primary component of cosmic rays in the stratosphere[^8] show that the intensity of this field apparently exceeds the intensity of the anomalous field of seas and oceans.

V. L.

CITED LITERATURE

1. N. Umov, Construction of the Geometric Image of the Gauss Potential as a Method for Finding the Laws of Terrestrial Magnetism, Selected Works, Gostekhizdat, 1950, p. 311.
2. P. N. Lebedev, Magnetometric Investigation of Rotating Bodies, Collected Works, Gostekhizdat, 1949, p. 229.
3. P. M. S. Blackett, Nature 159, 658 (1947); Uspekhi Fizicheskikh Nauk 33, 52 (1947); E. V. Stupochenko, Doklady AN 62, 477 (1948).
4. V. V. Shuleikin, Doklady AN 76, 57 (1951).
5. A. T. Mironov, Journal of Geophysics 6, no. 5 (1936).
6. L. A. Korneva, Doklady AN 76, 49 (1951).
7. V. V. Shuleikin, Doklady AN 71, 1057 (1950).
8. S. N. Vernov, N. L. Grigorov, and A. N. Charakhchyan, Izvestiya AN SSSR, ser. fizich. 14, 51 (1950).