книги из ГПНТБ / Pushkov N.V. Quiet Sun

the earth is observed precisely at the peak of such a merry-go-round; it then diminishes and the field gradually reverts to its normal state.

But how is a ring current formed? Where do the auroras come from? These questions are con­ nected because the theory of magnetic storms is closely bound up with the theory of auroral dis­ plays. To this there was no answer.

At what distances from us do these events oc­ cur? This wasn’t quite clear either, although Chapman believed that the electric current de­ veloped somewhere between three and five earth radii from the centie of the earth.

On the eve of the IGY, an American physicist S. Fred Singer put forth a new and extremely fruitful idea. His supposition was that currents responsible for the principal phase of magnetic storms are generated by particles captured by the earth’s magnetic field. Such particles should re­ volve about the earth and at the same time slip along spiral paths round the force lines of the magnetic field from one hemisphere to the other and back again.

Since electrons would be moving round the earth eastwards, and protons westwards, the re­ sult would be a current in the westerly direction. But then it would have the shape not of a circle lying in the plane of the magnetic equator, but of a whole current stratum, a current belt em­ bracing practically the whole earth from one magnetic pole to the other.

This layer of current would follow the force lines of the magnetic field; it would come closest to the earth at the magnetic poles and be farthest away at the magnetic equator. The most intense

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c u r r e n t H o w s n e a r t h e e q u a t o r ; a n d p r o t o n s a r e

a t m o s p h e r e a n d g e n e r a t e p o l a r a u r o r a s .

S u b s e q u e n t o b s e r v a t i o n s o f n a t u r a l p a r t i c l e s i n

t i o n p r o d u c e d i n a t o m i c b o m b e x p l o s i o n s a t h i g h a l t i t u d e s f u l l y c o n f i r m e d t h e t y p e o f p a r t i c l e m o ­ t i o n p r e d i c t e d b y S i n g e r . T h a t i s w h y a l l m o d e r n t h e o r i e s o f m a g n e t i c s t o r m s , i n c l u d i n g t h e r e n o v a t ­ e d t h e o r y a d v a n c e d i n r e c e n t y e a r s b y C h a p m a n

l a y e r i s g e n e r a t e d d u r i n g m a g n e t i c s t o r m s .

A l l t h i s w a s o n l y h y p o t h e s i s , t h o u g h a v e r y l i k e ­

a n d i n s u f f i c i e n t q u a n t i t i e s a n d t h a t t h e g e o m a g ­ n e t i c p o l e c h a n g e s w i t h i n c r e a s i n g d i s t a n c e f r o m

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

n e t i s m p r o p o s e d b y G a u s s .

T h e o n l y w a y t o v e r i f y t h i s h y p o t h e s i s w a s t o

a n d r o c k e t s t h a t w e r e b e g u n d u r i n g t h e I G Y c o n ­ s t i t u t e d a s i g n i f i c a n t s e g m e n t o f t h e I Q S Y p r o ­ g r a m m e . T h e y d r a s t i c a l l y c h a n g e d o u r c o n c e p t i o n

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of the space about the earth and about the struc­ ture of the magnetic field at large distances.

A l t h o u g h i n v e s t i g a t i o n s o f t h e f i e l d a n d p a r t i ­

c l e s a r e c l o s e l y b o u n d u p a n d t h e r e s u l t s o f o n e

The first experimental indications of the pos­ sible existence of an extra-ionospheric current layer were obtained during the flight of the So­ viet space rocket Luna 1. It was launched moonwards on January 12, 1959, and, passing at about 5 to 6 thousand kilometres from the moon, be­ came the first man-made planet of our solar sys­ tem.

When the probe had receded to from two to five earth radii from the centre of the earth, the magnetometer on board noted a substantial de­ crease in the field intensity compared with what should have been expected on the basis of Gauss’ theory for the case when all field sources lie inside the earth. At the same time, charged-par­ ticle counters recorded accumulations of highenergy electrons at these distances. The decrease in intensity of the magnetic field was interpreted as an indication of a current layer.

Similar results at about the same distance were obtained by Luna 2 which was launched on Sep­ tember 12, 1959. The American satellite Ex­ plorer 6, in August-September 1959, repeated measurements of the magnetic field at distances from two to eight earth radii both during the qui­ escent state of the field and during magnetic storms.

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Soviet Electron 2 space station

These measurements showed that there is a de­ crease in the field intensity at three to four earth radii from the centre of the earth both in quiet and excited fields. But during magnetic disturbances it becomes larger.

Important measurements of the magnetic field in this region of space were carried out during the IQSY by the Soviet space vehicle Electron 2.

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Between January 30 and May 5, 1964, the satel­ lite had two instruments functioning: one more sensitive than the other. This made measurements possible out to distances of 3 to 11.6 earth radii.

Long-term measurements of Electron 2 both on the outgoing and incoming branches of its trajectory established quite definitely that at dis­ tances from three to five or six earth radii the actually observed field is always less than the theoretically calculated field. On days of magnetic

At still greater distances the observed field is more than the calculated one, and this difference ordinarily increases with the onset of a magnetic disturbance.

Unlike the Soviet investigators, their Ameri­ can colleagues focussed attention on elucidating the nature of the field that “resides” at a distance of about seven earth radii and more. Here, too, very interesting peculiarities were discovered. Explorer 6 and, later, Explorer 10 launched in March of 1961 demonstrated that the perturbing field, which makes the observed field different from the theoretically calculated one, is in a di­ rection opposite that of the sun. The idea arose that this effect might be accounted for by the action of the solar wind.

A theoretical consideration of the interaction of the solar wind (solar plasma moving at suoersonic speeds) with the earth’s magnetic field, which was initiated by Chapman and Ferraro, led scientists to very interesting and, at first glance, quite exotic conclusions. It was found that the earth’s magnetic field at large distances

8 6

The field of uniform magnetization falls off the same way in all directions: in proportion to the cube of the distance from the centre of the earth. At two radii from the centre, it would be eight times weaker than at the earth’s surface, at three radii, 27 times weaker, etc. And there would be no definite boundary line.

But if there is a constant solar wind, the earth's magnetic field would be limited to a certain re­ gion called the magnetosphere. The boundary of the magnetosphere—the magnetopause—would come closest to the earth at the subsolar point, that is, where the sun is in the zenith. On the morning or evening side of the earth, it would recede from our planet.

As to the location of the boundary on the night side, there are two different hypotheses: the open and the closed magnetosphere. The propounders of the open magnetosphere believe that part of the force lines of the magnetic field are broken and connected to the earth at one end only, the other end going off to astronomic distances. The noted American theoretician A. Dessler believes that the magnetosphere extends to distances of 20 to 50 astronomical units on the night side (the astronomical unit is the earth-sun distance).

S u p p o r t e r s o f t h e c l o s e d m a g n e t o s p h e r e p i c t u r e

i t i n t h e f o r m o f a g i g a n t i c d r o p , t h e e l o n g a t e d

e n d o f w h i c h m a y e x t e n d o u t t o s e v e r a l t e n s o f e a r t h r a d i i o n t h e n i g h t s i d e o f t h e p l a n e t .

T h e m a g n e t o s p h e r e i s s u r r o u n d e d b y a m a g ­

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

p a r t i c l e s o f t h e s o l a r w i n d r e f l e c t e d f r o m t h e

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magnetosphere. Unlike the magnetosphere where the magnetic field is stable and regular, the field of the shell experiences constant variations in magnitude and direction due to numerous local eddies.

The configuration and behaviour of the mag­ netosphere depends on the properties of the solar wind interacting with it, its composition and the velocities of the constituent particles, the pres­ ence or absence in it of a magnetic field, on wheth­

the various authors proceeded from different con­ jectures about the solar plasma and its interaction with the magnetic field of the earth. Quite natu-

A model of the magnetosphere (cross-section). Black circle in centre represents the earth. Curves indicate magnetic lines of force

rally, they arrived at different models of the magnetosphere.

T o d a y i t i s p o s s i b l e t o o b t a i n i n f o r m a t i o n a b o u t

y o n d i t a n d m e a s u r e t h e c o r p u s c u l a r r a d i a t i o n a n d

t h e m a g n e t i c f i e l d .

The Soviet and American interplanetary sta­ tions of the Luna, Mars, Venus, and Mariner series have, in their extended voyages, repeatedly entered streams of solar plasma and sent back information about it. The density has been found to vary from one to ten protons per cubic centi­ metre. Stream velocity may range from BOO to 700 km/s. Its magnetic field is rather weak, on the average about 5 gammas.

Very important data about phenomena at the boundary of the magnetic field have been obtained by the American space vehicles Ex­ plorer 12 and Explorer 18 and the Soviet vehicles Electron 2 and Electron 4 launched into very elongated orbits. Explorer 18, which also goes by the name IMP 1 (an acronym for Interplanetary Monitoring Platform), was designed mainly for measuring the interplanetary magnetic field. Its original apogee equalled 197,000 km. American satellites of this type are orbitally inclined about 30° and consequently yield information about events near the equatorial plane. Soviet Electron vehicles are launched into orbits inclined about 60°, thus covering phenomena in the higher lati­ tudes.

Measurements made by Explorer 18 showed

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Space measurements of the magnetic field and the distribution of charged particles gives us re­ liable information about the magnetic sphere of the earth. However, our knowledge of this region, which plays so important a role in regulating solar effects on the earth, is accumulating at a very slow rate. Most findings so far relate mainly to the day side of the earth. Little is known about the night side.

The enormous size of this region does not per­ mit us to judge about events throughout its thick­ ness on the basis of the flight of a single satellite. Recall that the orbital period of Explorer 18 was 93.5 hours and most of this time it was outside the magnetosphere. To obtain simultaneous syn­ optic data, measurements will have to be made by a system of satellites flying in different orbits and at various distances from the earth.

vehicles.

Electron 1 and Electron 2 were launched on January 30, 1964, thus, as it were, ushering in the International Quiet Sun Year. These two satel­ lites launched by a single powerful rocket com­ prised a unified system performing in a single ex­ periment. The angle of inclination of their orbits to the plane of the earth’s equator was about the same—close to 60о50'.

But Electron 2 was farther out with an apogee of nearly 11 earth radii (close to 68 thousand kilometres), while Electron 1 had an apogee of only 7,145 km. The orbital periods were, accord­ ingly, 2 hours 49 minutes and 22 hours 36 min­ utes.

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