книги из ГПНТБ / Pushkov N.V. Quiet Sun

Columbus of magnetic space was the third Soviet satellite, Sputnik 3, launched in 1958. This was followed by the American Vanguard satellite. These space vehicles were very successful in mak­ ing measurements of the magnetic field. They demonstrated that magnetic surveys via satellites make for a more precise analysis of the earth’s magnetic field than is possible by ground-based data alone.

O n t h e b a s i s o f a n a g r e e m e n t b e t w e e n t h e g o v ­

l i t e - d i r e c t e d m a g n e t i c s u r v e y o f t h e e a r t h d u r i n g

t h e I Q S Y .

Magnetic surveys of circumterrestrial space have certain advantages over other types of sur­ veys. To make magnetic surveys over a total route of 200,000 miles, aircraft were in operation for several years. A satellite can cover the same distance in less than a day. What is more, there are no inaccessible places. Orbiting at a variety of altitudes, satellite vehicles report on how anom­ alies decay with altitude, and this helps to pin­ point the location of their sources relative to the earth’s surface.

Repeated magnetic surveying from satellites will help solve a most interesting problem: the variation of the magnetic moment of the e^rth with respect to time. Very important facts about the structure and behaviour of the magnetic field at large distances from the earth have been ob­ tained by the Soviet Electron satellites and the American Explorer series that were launched in accordance with the IQSY programme. Their highly eccentric orbits allow them to make pe­

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riodic cuts through the magnetosphere and report on events inside it, on the boundary lines and beyond, out in the interplanetary magnetic field.

The whole world-wide magnetic survey will take a good number of years yet, despite the so­ phisticated space and ground technology. How­ ever, a very substantial foundation of this great undertaking has already been laid in the Inter­ national Quiet Sun Year.

Earth currents

These currents were first detected, as is often the case, because of trouble. Last century saw the first long-distance telegraph lines put into service. And the earth served as their return line. It was soon found that communications were at times suddenly disrupted. Telegraph apparatus would spontaneously tap out gibberish, and the tension in the lines grew to prohibitive magni­ tudes. The time of such disruptions coincided with the onset of intense magnetic storms and auroral displays.

Further investigations brought to light the fact that there are always stray electric currents wan­ dering about inside the earth; they are usually rather feeble and change both in magnitude and in direction. When they get into telegraph lines earthed at both ends they disrupt communica­ tions. Earth currents were put under surveillance, which was not difficult because no complicated equipment was needed. In fact, it suffices to put iron rods into the earth a few hundred metres

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apart and connect them with cable lines. The current intensity in the lines may be measured with a galvanometer.

Ordinarily, when the magnetic field is quies­ cent, the earth currents are weak and the differ­ ence of electric potential between two points on the surface does not exceed several millivolts per kilometre. But when the magnetic field of the earth comes under the action of solar corpuscu­ lar streams it gets excited and induces much heavier earth currents with potential differences of the order of hundreds and even thousands of millivolts per kilometre.

An earth-current storm of this magnitude is no simple affair. For instance, on April 16, 1938, earth currents disrupted communications on long-distance telegraph lines almost over the en­ tire Soviet Union. One can easily imagine the potential disasters this is capable of. Quite under­ standably, after this occurrence, the Soviet Union set up a permanent information service on the state of the magnetic field; it later grew into a forecasting service of magnetic disturbances.

Despite the simplicity of earth-current research and the obvious necessity of such studies, little headway was made for a long time in this sphere. Strangely, the stumbling block was in the form of trams, electrified railways, and the under­ ground railways operating on direct current with the rails as the return line. The large stray cur­ rents generated by them interfere with the regist­ ration of the comparatively weak earth currents. Also, interest in earth currents somehow de­ clined when it was found that their behaviour de­ pends on the geology and orography of the vi­

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cinity, for this complicates deciphering planet­ wide peculiarities in current variations.

Investigations were greatly expanded during the International Geophysical Year. Sixty sta­ tions set up at numerous magnetic observatories in tens of countries of the world, including the particularly interesting regions of the Arctic and Antarctic, carried out continual observations of this phenomenon.

During the IQSY, new stations and a major portion of the earth-current stations set up dur­ ing the IGY continued the observational work. Particularly gratifying was that the number of such stations increased on the American conti­ nent. One was established in Cuba. Soviet resear­ chers opened up 18 stations covering an immense area between Alma-Ata, Murmansk, Petropavlovsk and Alushta (in the Crimea).

The Antarctic was also attacked scientifically. The Soviet ship carrying members of the first So­ viet Antarctic expedition in 1956 set out with everything imaginable on board, but the biggest surprise to anyone inspecting matters would have been the earth loaded in the hold, .lust soil on a trip to the ice continent so that electrodes could be inserted in order to study earth cur­ rents. Later, however, scientists learned how to do the trick without imported earth.

It was found that in polar regions disturbances and real storms are especially frequent and in­ tense. Of course, during large magnetic storms, heavy earth currents “flow” even in medium lat­ itudes, but their real domain is the far north and the far south, which are the customary areas of the auroras.

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Earth currents come with changes in the mag­ netic field. Quite natural, therefore, that there should be much in common between them: the frequency of both depends on the cycle of solar activity and both have a tendency to recur every 27 days. Whence their kinship with the aurora, variations in the ionosphere, and even with dis­ ruptions of long-distance communications. When in 1961 and 1962 American scientists correlated earth-current pulsations with frequent and small beats and brightness changes of auroras over Alaska, a remarkable coincidence was found in

Unlike ordinary magnetic records, the registra­ tion of earth currents is conducted with great rapidity: this makes it possible to record oscilla­ tions with a period of only a few seconds and catch even very slight and extremely rapid changes in the magnetic mood of the earth. What is more, earth currents, these “moles digging in the earth”, have been found capable of recording certain processes that occur at high altitudes.

For example, when, prior to the Moscow agree­ ment on the prohibition of atomic explosions in the atmosphere, the Americans exploded three nuclear devices at 500-km altitude over the South­ ern Atlantic, scientists of many countries were able to determine the times with great accuracy on the basis of earth-current records. The point is that despite the low yield of these devices, they caused disturbances in the magnetic field that were accompanied by characteristic rapid pulsa­

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Just before the beginning of the International Quiet Sun Year, a variety of magnetic field and earth-current pulsations was detected and given the poetical name of pearls. These are micropul­ sations with a period of from 0.3 to 2.5 seconds; they are detected on the basis of characteristic deviations that are superimposed on (“threaded onto”) the ordinary record.

The pearls frequently recur on the trace of the record at equal time intervals, usually every few minutes. It is believed that these embellishments are the sun’s gift to the earth; they are apparently associated with the movement of blobs of solar plasma along the force lines of the magnetic field and with their drift round the earth. Another surmise is that these pulsations are caused by hydromagnetic waves of a special kind that arise on the boundary of the earth’s magnetic field un­ der the action of the solar wind.

W h i c h o f t h e s e h y p o t h e s e s i s c l o s e r t o t h e t r u t h

Today, on the initiative of Soviet scientists, workers in tens of countries are co-ordinating efforts for joint investigations into the “Upper Mantle of the Earth”, the aim being to extract information about the structure of this planet of ours, about the inner regions of the globe, of which, to our shame, we know so little. Earth cur­ rents should be a great help in this work. A good deal of information concerning the internal struc­

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Union successfully reached the 16-km level. The physicist Verigo, to slow down the dangerous descent, left the gondola in a delayed parachute jump from this extreme altitude. That same year physicist Carl Anderson and pilot Stevenson of the United States, reached 22,066 metres in the balloon Explorer II.

All these efforts and sacrifices were not sport­ ing achievements. Piccard, Usyskin, Verigo, An­ derson, and Prokofyev were not out to chalk up records. They were after cosmic rays and studied the variation of conductivity of the air and the radiation intensity as a function of altitude.

At the same time, investigations continued into the ability of radiation to penetrate through var­ ious media. Radiation was measured in ioniza­ tion chambers protected by lead shielding of var­ ious thickness, in deep mine shafts, in clefts in glaciers, in mountain lakes at various altitudes, and aboard submarines. Physicists found that it could be detected with sensitive instruments even under layers of water three kilometres in thick­ ness, though it was weakened by a factor of

100,000, 000!

Studying the absorption of radiation by lead, researchers found that it could be divided into two components: soft (absorbed in a layer of lead of thickness 8 to 10 cm) and hard (capable of penetrating thicker shielding without perceptible absorption). This at first glance purely formal division had a profound physical meaning. Sub­ sequently, it was learned that the different pene­ trating ability is connected with the composition of the particles that make up the radiation.

At this time, ionization chambers were being

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