Magnetic storms: Their geometrical and physical analysis, and their classification

M A G N E T I C S T O R M S : T H E I I ~ G E O S I E T I Z I C A L AND P H Y S I C A L A N A L Y S I S ,

AND T H E I R C L A S S I F I C A T I O N

SYDNEY CKAt'3I:YN Geophysical Institute, University o/Ahvska

and High Altitude Observatory, Boulder, Colorado,*)

1. T Y P E S O F G E O M A G N E T I C C H A N G E

The Earth 's magnetic field, which originates in the liquid core of our planet, changes in three essentially different ways. One is the slow secular variation. This also comes from the core. Its changes have a magnitude, over long periods of t.ime, comparable with that of the field itself. Thus, they are of order ten thousand gammas (I gamma - I0 -s gauss.). In the Course of geological ages the field may even be reversed in direction, perhaps many times. The intensity may vary by a notable fraction in as short a t.ime (geologically regarded) as a few milienia.

The other two types of magnetic variation are called t r a n s i e n t because their typical course involves much shorter intervals of time, less than one or a few days. One of these two types of transient change, indeed, is periodic in a solar or lunar day. The range of the dai ly v~triations is much less than that of the secular eha.nges, though the r a t e of change is greater. The amplitude of the daily changes is at most of order 100 gammas. They are produced a b o v e the Earth, at relatively low levels in our ionosphere. The cause is dynamo action by daily varying flow of ionized air across the geomagnetic field.

Unlike the lower atmosphere, the geomagnetic field has no significant an- n u al variation.

The second type of transient change is irregular, non-periodic. I t also has its source outside (above) the Earth. Its general name is magnetic disturbance or activity. Its more intense forms are called magnetic storms. Like the regular daily variations magnetic disturbances and storms can be regarded as manifest- ing the superposition, on the main field extending outwards from the core, of an additional magnetic field. This field is called the D field (D for disturbance). The main field may likewise be called the M field.

Though these transient fields originate above the Earth, they induce electric currents within the Earth, whose magnetic fields contribute to the recorded magnetic changes at the Earth's surface. Methods are available t.o separate these secondary parts of the transient fields from the primary parts, of external origin.

In its distribution over the Earth the D field differs remarkably from the M field and from the daily variation fields S (solar daily) and L (lunar daily). The M field intensity increases rather regMarly from low to high latitudes, by

factor of about 2. The S and L fields are stronger over the sunlit t han over the dark hemisphere -- because the currents that generate them can flow more freely in the well ionized d a y t i m e ionosphere. The D field, however, common- ly has its greatest intensity in and near the auroral zones at night. These Zones are centered on the geomagnetic axis, and have an angular radius of about 23 ~ .

*) T h e r e engaged in a progn~m of r e sea rch sponso red b y the N a t i o n a l B u r e a u of S t a n d a r d s a n d t h e Ai r Force Geophys ica l Resea rch D i r ec to r a t e .

30 Studia geoph, et geod. 5 (1961)

Magnetic Storm.s: Their Get, metrical and Physical ztnaly.~is, and their Class.iJicatio~

Near them the changes may be as great as 2000 7, while at the same time, at many low latitude stations, the disturbance is no more than one or two hundred gammas.

The changes in the three components of the field are recorded at numerous magnetic observatories widely spread over the Earth. In studying the S, L and D fields the slow secular changes need little consideration. But the separation of the daily varying S and L fields from each o~her and from the D field is not ahw~ys easy. This is partly because the S and L fields change somewhat from day to day -- doubtless owing to what we may call large-scale weather in the ionosphere (of. Chapman 1960).

2. S T U D Y O F T I I E D F I E L D

The study of the D field was naturally first directed to its strongest, mani- festations, namely magnetic storms. These have been longest observed in middle and low latitudes, and only more recently, over fewer years, in high latitudes. The directors of individual observatories began the study by examinil~g their own magnetic records. They saw that many storms begin quite suddenly, with a rapid increase in the (northward) horizontal component of the field, H. The ssc (storm sudden commencement) increase often persists for an hour or more, usually with fluctuations. Then H decreases by a larger amount, to values distinctly below normal. After an interval ranging from about half a day to a day or more, H begins to return to its normal level. These typical changes are often partly obscured by irregular fluctuations.

The characteristic properties of magnetie storms in middle and low latitudes can be welt studied from the records of single observatories or groups of observatories. The task becomes more difficult with increasing latitude, for two reasons. One is the smaller number of storms to be studied, in the shorter period of re cord. The other and greater difficulty is the enhanced intensity and variability of the D field changes in the higher latitudes, and especially near the auroral z o n e s .

A groper conception of the nature of the D field cannot be derived from studies of the records of one or a few observatories. The morphology of the D field -- its geographical distribution and its characteristic sequence of time changes -- requires synoptic study.

3. G E O M E T R I C A L A N A L Y S I S O F T t I E D F I E L D ; Dst A N D D S

The most extensive synoptic study of the a v e r a g e properties of the D field is one made during recent years at the University of Alaska, by Dr. M. Sugiura in conjunction with me (1958). Over 300 storms with recognizable times of commencement were dealt with, using records from 19 obser~'atories over a period of 43 years (1902--1945). The 346 storms were divided into three groups aeeording to their intensi ty-weak, moderate and great. Each group was studied separately in t.he same way.

Defining storm time for each storm as reckoned from its commencement, the average variation from that time onwards was found for each magnetic element at each observatory. This average course of change is called the storm-time variation, and denoted by D,~t (st for storm t_ime).

In obtaining Dst, the variations are combined for storms at different epochs of Greenwich or universal time (UT). These epochs were spread fairly uniformly over the 24 hours of UT. Consequently Dst represents the storm changes aver-

Studia geoph, et good. 5 (I~61) 3I

S. Chapman

aged at each epoch of storm time over all local hours. Geometrically this signifies that the Dst variation, at each epoch of storm time, in each gm latitude, is the change averaged round the circle of gm latitude.

The next step is to determine, for each latitude and each s torm time epoch, how the D field varies with longitude round the circle of latitude. In the main the distribution depends on the local time, that is, the longitude relative to the noon meridian, or as viewed from the Sun. This part of the D variat ion and D field is denoted by D S - - it indicates the distribution of the D field, relative to its mean value, round each circle of latitude relative to this solar-defined longitude or aspect. The results consist of sets of curves, each see referring to one magnetic element and one epoch of storm time. Each set has one curve for each of a series of latitudes.

Thus fo r e a c h e l e m e n t and e a c h l a t i t u d e we have one D s t curve, on a time basis chosen as covering the duration of the main storm changes. In the s tudy by Sugiura and myself, this interval was three days. In addi t ion we have a series of D S curves, one each for a series of storm time epochs. Thei r abscissae may be expressed in local time (24 hours), or, better, in geometrical terms, as longitudes relative to the meridian half plane passing through t h e Sun. These longitudes may be reckoned from zero at the midnight meridian (local time 0 h) through the meridians of dawn (90~ noon (180 ~ and sunset (270~ back to the midnight meridian (360 ~ or 0~

4. D EQUIPOTENTIAL CHARTS AND POSSIBLE C U R R E N T LINES

These various sets of curves represent the average changing distr ibution of the D field over the Earth's surface, as a function of storm time. Besides these average or typical features, each storm has its own individual f luctuations, corresponding to an additional field Di of irregular disturbance. I t is not easy to picture the distribution of a vector field over the Ear th except im the simplest cases (such as the field of gravity). Hence it is naturally rather diff icult to visual- ize the morphology of the D field. But the D field at the Ear th ' s surface has a magnetic potential. This is a scalar function, whose distr ibution over the :Earth can easily be indicated graphically. The potential of the p r imary and secondary (external and induced) parts of the surface D field can each be so represented. I t is appropriate to represent the internal part by a set of equipotential lines on a spherical surface somewhat smaller in radius t h a n the Earth. Similarly the potential of the primary, external field can be shovcn by equipotential lines over a spherical surface somewhat above the Ea r th .

Such an external chart also represents a system of electric current flow over the surface, tha t could produce the external part of the D field observed at ground level. As such, it indicates in a rather simple way the distr ibution of the D field over the Earth.

Thus a series of charts showing current lines over a concentric sphere, one chart for each of a series of storm time epochs, can indicate t h e changing morphology of the observed D field. Separate charts can be drawr~ for the Dst and D S parts of the field. The combined chart represents the whole (average) D field.

But although the charts show current systems that c o u l d produce the D field, these are not necessarily the currents that do produce the field. With- out further consideration, the charts must be regarded as only a convenient geometric mode of indicating the distribution of the surface D ~ield.

32 Stud ia g e o p h , e t geod . 5 (1961)

M .agnetic Storms: Their Geome, trieal arid Physical Analysis, and their Classi]ication

)ioreover the division of the D field into the Dst and DS parts is only a geometrical one -- into a part symmetrical about the geomagnetic axis, and the remaining part that varies with longitude relative to the Sun.

The true distribution of the external currents that produce the primary part of the D field can only be inferred from additional p h y s i c a 1 data or inferences. The physical analysis of the surface field, unlike the geometrical one, is still tentative.

Without going into the many detailed considerations on which my conclusions are based, I will describe my conception of the results of the physical analysis.

5. S O L A R S T R E A _ ~ I S A N D T H E I R I ~ N ~ T E R - A C T I O ~ ~

W I T H T H E G E O M A G N E T I C F I E L D

The D field has three distinct main sources, and all three are the results of one fundamental cause. This is a stream or cloud of neutral ionized gas ejected earthwards from the sun. The gas consists mainly of protons and electrons, and its speed is of the order 1000 km/second. Thus its typical travel time from the sun is of order 1.5 • 105 seconds, less than two days. The lateral extent of the stream or cloud is a large multiple of the Earth 's radius. The Ear th is therefore a relatively very small object, over which the stream flows.

The geomagnetic field greatly changes the motion of those particles of the stream whose paths, if undisturbed, would pass within a few Ear th radii of the Earth 's center. ~I:~them~tical prediction of the course of events in the region around the E~rth is extremely difficult. So far it has made but little progress. Partial theories have been developed, however, dealing with idealized model situations that illustrate some features of the problem.

I t appears that in the plane of the geomagnetic equator, and for some distance above it and below, the charged particles of the typical stream will be prevented from approaching nearer than a few Earth radii. Thus a hollow will be formed in the stream. The invisible magnetic field acts as a barrier, shielding the lower latitudes of the Ear th from the impact of the stream particles. Those approaching the Ear th most directly will be turned backwards almost in their tracks. Those that might graze the Earth, or pass by it at a small distance, if undisturbe d, will be deflected away sideways.

6. T I l E DCF ( C O R P U S C U L A R F L U X ) P A R T O F T H E D F I E L D

At the front of the stream, bordering the hollow carved in it, the protons and electrons will be deflected in opposite directions. L~)oking towards the Ear th from the Sun, with the northern hemisphere seen above and the southern below, the protons will move to the right, the electrons to the left. This constitutes eastward electric current flow in the equatorial and low latitude part of the surface of the hollow. The electric current will at least to some extent shield the rear of the stream from the geomagnetic field, and will add to the geomagnetic field within the hollow. This addition is of the kind observed at the Earth 's surface in the lower latitudes at the sudden commencement of the storm. The stoppage of the stream, at its first, onset, will be achieved in a time of order 100 seconds. This interval will cover the development of the surface electric current, and of its magnetic field around the Earth. If the Ear th had no atmosphere, the magnetic field changes would be transmitted with the speed of light. The additional field would then effect the whole earth simultaneously

Studia geoph, et geod. 5 (1961) 33

S. Chapman

to within a fraction of a second. Actually the atmosphere ex tends outwards over several Earth radii, and its outer part is ionized. The field changes are propagated through this medium with reduced speed, of the order 1000 kin/second. As the dimensions of the stream-hollow are of the order of a few Ear th radii, there will be differences of the order 10 to 30 seconds between t he time of the initial change in the field -- the sudden storm commencement or ssc -- at different points over the Earth.

If the stream were of brief duration the electric currents over i ts inner surface near the Ear th would soon cease, when the onflow ended. The increase in the magnetic field recorded on the Earth would be likewise brieL But if the stream flow continues for hours, the currents and their magnet ic field will similarly persist. This may often happen, though the stream dens i ty and speed may vary. This will cause the hollow to vary somewhat in size, and the currents and their disturbing magnetic field will fluctuate.

This magnetic field is one of the three main parts of the D field during a magnetic storm. I t depends essentially on the continuance of the corpuscular flux. Hence it may be denoted by D C F .

Model theories have sought to relate the scale of the hollow to the magnitude of the momentum flux of the stream, n m v 2 (Chapman and Ferraro 1931 a, b; 1940; Ferraro 1952). The surface of the hollow will be nearest the Ea r th ' s center on the line joflfing the centers of the Earth and Sun. Let the dis tance of this "ver tex" of the hollow from the Earth 's center be Z Ear th radii. Then theory suggests that

Z = [ H ~ / S = E ] ~.

where H 0 denotes the Earth 's equatorial surface magnetic in tensi ty (0.3 gauss) and E - - H 2 / 8 ~ ( -~ nmv~-). Here H denotes the geomagnetic field a t the vertex, n-----number density, m - ~ mass, v----velocity of solar corpuscles (protons). The amount of increase of northward component (H) is given by

H o / S Z 3 .

For v ---- 1000 km/sec, values 3, 5, 10 for Z correspond according to this formula to number densities n of order 300, 14 and 0.2/cc. The corresponding magnitudes of the ssc change of H in low latitudes are 140% 30u and 4y, respectively. These estimates allow for a 50% increase of the direct D C F field by the field of the corresponding induced earth currents.

7 . T H E DP P A R T O F T I - I E D F I E L D : G E N E R A T E D I N P O L A R

R E G I O N S

Another main part of the D field observed at the Earth 's surface is produced b y the entry of particles hlto the ionosphere in high latitudes. :Presumably these are from the parts of the stream originally flowing at some distance above and below the geomagnetic equatorial plane. Theory has not yet succeeded in showing the paths followed by the particles as the geomagnetic field deflects them to enter our atmosphere. The injection is greatest along the nor thern and southern auroral zones. Two obvious consequences are increased ionization of the atmosphere, and the excitation of auroral luminosity. Doppler shifts af- fecting hydrogen lines in the auroral spectrum indicate that the particles include protons descending with speeds up to 3000 kin/see. The protons reveal their entry by emitting photons, after they have picked up an electron during their descent. The presence of electrons among the entering particles is shown

�9 3 4 Studia geoph, et geod. 5 (1961)

Magnetic Storms: Their Geometrical and Phy~'cal Arudysis, and their Classi]ication

by the detection of X-rays, down to levels of no more than 30 km, in the auroral zone. The X-rays are produced by a small minority of the electrons (of order one in a thousand) that make particularly close collisions with nuclei of atmospheric atoms and molecules. The energy of the protons ranges at least up to about 50 key, tha t of the electrons up to 50 or 100 key, though values of 10 to 30 key are probably more frequent.

The apparent energies of the protons and electrons in the stream are smaller -- about 5 key for the protons, and much less for the electrons. These estimates correspond to their speeds as judged from their travel time, Sun to Earth. Possibly some particles have greater energies and speeds, corresponding to internal motions in the stream, such as spiral motion round lines of a magnetic field carried away from the Sun. Alternatively the stream particles tha t enter our atmosphere may gain energy in the geomagnetic field by some process not yet understood.

The entry, of the particles into the auroral atmosphere is accompanied by the generation of strong currents along the zone, or along part of it. These currents seem to flow at E layer levels. The direction may be westward or eastward. The westward currents seem to be the more common and intense. Being rather nar- rowly limited, they are called electrojets. From the auroral zone the current circuits are completed over the polar cap and over the major belt of the Ear th between the two auroral zones. I t seems likely tha t their driving forces come in some way from the entry of the particles into the auroral zones from outside. The geomagnetic field pervading the ionosphere renders the electric conductivity anisotropic. Westward current flow corresponds to an electric field (or electro- motive force, emf) directed nearly southward, and eastward flow to a northward emf. I t may result from a difference between the mean latitudes at which the protons and electrons enter (Martyn 1951, Akasofu 1960).

The part of the D field produced by these electric currents in our atmosphere originating in the polar (auroral) regions, may be called the polar part, and denoted by DP. This part is sometimes set up simultaneously, or almost so, with the D C F part. In middle and higher latitudes the two fields may be opposed, so that the H sac may be a decrease, at least briefly, instead of the increase observed in lower latitudes.

The magnetic anisotropy of ionospheric conductivity enhances the D P currents in a narrow belt along the magnetic equator on the daytime side of the Earth. This parallels the well kno~-n increase of the S and L fields along this belt. This belt current is called the equatorial electrojet.

8. T H E R I N G C U R R E N T P A R T DR O F T H E D F I E L D

The third main part of the D field corresponds to a decrease of the geomagnetic field at the surface of the Earth. This betokens the presence of a westward current encircling the Earth. The existence of such a "ring" current was suggested by StCrmer (1911, 1955) in an untenable form and size, on the basis of his untenable theory of the aurora. The idea was revived by Schmidt (1917) on the basis of the magfletie storm evidence -- but without proposing any estimate of the location and size of the ring. Ferraro and I (1941) gave reasons for estimating its radius as a few Earth radii, comparable with the size of the hollow carved in the solar stream by the geomagnetic field. We speculated how the ring current might be set up, and examined the stability of the ring. We pictured it as a simple toroid, with protons and electrons flowing round it with

Studia geoph, et geod. 5 (1961) 3~

S. Chaperon

slightly different speeds. Its equilibrium required that the current direction be westward: and also that there should be a positive charge on the inner half of its surface -- facing the Earth -- and a negat, ive charge over the other half. Charges would escape from the surface and spiral along the geomagnetic lines of force towards the auroral zones. The protons would arrive at a mean latitude less than that reached by the electrons -- giving a northward emf, as indicated by Martyn (1951). Though we showed that this ring current would be stable for certain types of perturbation, Herlofson (1959) later showed t h a t for o t h e r kinds it would be unstable.

Singer's (1957) speculative studies of magnetic storm theory led him to the conception that during such storms the Earth is encircled by a different kind of belt. He conceived that the main motion of the charged particles of which it is composed would be northward and southward. Their paths would part ly follow the lines of geomagnetic force, but would also include a drift around the Earth. The electron drift would be eastward, the proton drift westward -- con- stituting a westward current.

These ideas gained striking support from the discovery and exploration by Ear th satellites of the belts of energetic protons and electrons that encircle the Earth (Van Allen et. al., 1959a, b; Vernov 1959). Dessler and Parker (1959) and Akasofu (1960) studied the westward current associated with such belts, and made an important correction to this part of Singer's theory.

The belts are found to undergo important changes, of loss, decay and re- newal. A beginning has been made in the study of the association of these changes with solar, auroral and magnetic storm phenomena. Much, however, remains uncertain and mysterious.

The part of the D field produced by this westward ring current m a y be denoted by DR. During a typical magnetic storm this DR field grows, and later decays. ~Iost of the .Dst field-change during the main phase of a magnetic storm, in which H is decreased, may be at tr ibuted to the ring current. The .DR part. of the field endures longer than ti~e DCE and DP parts. The recovery of H from its storm decrease may extend over many days, into times when the storm is well over, and the magnetic activity is low.

9. T H E T I M E D E V E L O P M E N T O F T H E P A R T S

DC_F, DP A N D D/~ O F T H E D F I E L D

Thus the proposed physical analysis of the D field may be symbolized by the equation:

D = DCF + DP ~,- DR.

Each of these three parts of the field has characteristic properties. All three contribute to Dst, but perhaps only DCF and, more notably, DP contribute to DS.

The part DCF has its source in electric currents that flow in the solar corpuscular stream near its hollow inner surface. Their distance from the Earth 's center is a few Earth radii. The currents flow mainly on the sunward side of the Earth, and the DCF field is stronger on that than on the night side of the Earth. The hollow surface will draw closer to the Earth if the density and speed of the corpuscular flux increase. The currents find the DCF field will t hen increase. Conversely they will decrease if the stream flow weakens. Such changes in the stream will therefore cause the DCF field, and hence the whole D field, to fluctuate. The DCF field will disappear when the stream ceases to flow. This may

,~6 Studla geoph, e t geod. 5 (1961)

Magnetic Stearin, s: Their Geometrical and Physical Analysis, and their Classification

happen in two ways. The stream or cloud of solar gas may be ejected from some storm center of the Sun during a solar flare. In this case the gas cloud will have a beginning and an end. Alternatively the emission may continue for days or weeks or months, from the same region on the Sun. Even so, the solar rotation will limit the duration of its onflow towards the Earth. Such a continuing stream would overtake the Earth in its orbital motion, and pass on beyond it.

The D P part of the field is due to currents flowing in the Earth 's ionosphere. They are most strongly concentrated along the auroral zones. The zones are the main seat of the driving emf's. How these emf's are set up is not yet clear. There is a seeonda~- daytime concentration of emTent along the equatorial electrojet -- a far outpost of the D P currents.

The D P currents begin early in the storm. Sometimes there is no perceptible delay of their onset after the D C F field is set up by the first stoppage of the corpuscular flux. This need not be surprising. The particles entering the auroral zone do so with speeds of some thousands of kin/see. Thus the time of their arrival may be not later than -- may even precede -- that of the arrival of the initial D C F field. This has to be propagated through the far extended atmosphere from the surface of the hollow to that of the Earth.

During the first minutes of a storm the D P currents sometimes undergo remarkable changes (Oguti 1956, Obayashi and Jaeobs, 1957). These changes seem to preclude dynamo action as the cause, such as produces the S and L daily variation fields. I t seems incredible that the airflow could change so quickly over a large region. On the other hand, rapid changes in the relative latitudes of entry of protons and electrons might quickly change, or even reverse, the emf's and the currents thereby driven.

The D P currents often fluctuate greatly during a storm. In many storms they appear as a series of pulses, each perhaps of duration of order one hour. Such a pulse is what Birkeland (1908), in his great pioneer study of magnetic storms, called a "polar elementrary storm", t ie distinguished between positive and negative "elementary storms", namely those that increase or respectively decrease H near the auroral zone. These correspond to the occurrence of eastward and westward auroral electrojets. Their strong field-changes in auroral regions are n.aturally associated with the more distant D P changes caused by the rest of the current circuit of which the electrojets are part. I regard such elementary storms as sub-divisions of a unitary magnetic storm. The duratiort of the whole storm includes the period of growth of the D R field to its maximum, and that part of the period of subsequent partial recovery of H in which the irregular magnetic fluctuations -- mainly due to D P -- are still active. The D P fluctuations are interpreted as corresponding to bursts of injection of particles into the auroral zones. These bursts are sometimes sudden and violent. This is indicated not only by rapid magnetic changes, but also by observations (Winckler et. al. 1959a, b) of the sudden entry of protons or electrons into the atmosphere. This is revealed by balloon-borne Geiger counters and ionization chambers. Satellite observations (Arnoldy et. al. 1960) sometimes indicate a simultaneous depletion of the Van Allen belts -- suggesting tha t there has been a sudden " d u m p i n g " of belt particles into our atmosphere.

Akasefu (1960) has found that the D P eleetrojet may show considerable northward or southward movement., in phase ~,dth similar movements of the aurora.

The D R part of the D field increases during the earlier part of a storm. After overcoming the initial increase of H, it produces a growing decrease. The period

stuclia geoph, et geod. $ (1961) 37

S. Chapman

of subnormal H, up to about the time of the point of inflection on t h e Dst curve, is called the main phase of the storm. The further period until t h e irregular changes cease is called the recovery phase. The maximum of the m a i n phase, when Dst reache its minimum, is generally attained more quickly, the greater the storm. In weak storms the maximum may not be reached unti l late on the second day, whereas in some great storms the main phase is a l ready over, and the further recovery of H towards normal is well advanced, by the end of the first day.

I0. MAGNETIC STORM DEVELOPMENT AND THE PRE-STORM BELTS

At present it is not easy to separate the field changes in a magnetic storm into their parts DCF, DP and DR. One complication is that the pa, rticles that enter the ionosphere and produce the DP field may not come di rec t ly from the solar stream. They may be particles that have been stored in the Van Allen belts for a time. If so, pulses of the DP field may continue after the stream flow on to the Earth has ceased, and with it, the DCF field.

The DR currents and field certainly seem to persist after this cessation of the stream. Schmidt (1917) suggested that the ring current m a y never die away. If so this would imply permanent presence of the Van Allen belts, even through sunspot minimum. As yet the belts have been observed on ly near sunspot maximum, and have w~ried considerably in intensity and extent, over the interval of investigation. As I suggested in 1951, the magnetic effects following the onset of a new solar stream may depend on the state, location a n d intensity of the pre-existing ~ing current (Chapman 1952). Sometimes magnet ic storms follow one another at short intervals, and the initial increase of H s ta r t s from successively lower levels, because the ring current enhancements during the earlier storms have only part ly disappeared. Sometimes a new s u d d e n commencement appears in a storm still active (Adams 1892).

Synoptic s tudy of many individual magnetic storms, with the ample magnetic and other data available during the IGY/IGC period, should m u c h improve our knowledge of magnetic storms in general. We should learn b e t t e r how to distinguish between the three parts DCF, DP and DR. This should tell us much about the solar streams, and about the magnetic influence and the changes of the Van .Mlen belts.

These main parts of the D field need to be studied also in relat ion to the magnetic pulsations that occur especially during magnetic storms (Troitskaya and ~'[elnikova, 1959).

II. PHYSICAL CLASSIFIC~%_TION OF MAGNETIC STORMS

The physical analysis of the D field into its three parts DCF, D P and DR may afford a convenient basis for the further classification of magnet ic storms. Birkeland recognized five types of magnetic disturbance, one of which was later identified with the enhancement of the S daily variation f ield over the sunlit hemisphere, following solar flares. The other four were "pos i t ive" and "negative . . . . elementary polar storms", and "positive" and "'negative" ,,equatorial storms". As ah'eady indicated, the first two of these m a y be regarded as D P sub-divisions of unitary magnetic storms, identified b y their cycle of Dst change. The other two (equatorial) may similarly be identif ied with the first and main phases of a unitary storm.

3 8 Studia geoph, e t g e o d . 5 (1961)

2dagnetic Storm.v: Their Geometrical and Physical Analysis, and their Classification

Apart from Birkeland's classification, the two criteria used to class magnetic storms are (a) the intensity and (b) whether the commencement was sudden or gradual. The usefulness of the two criteria is only supplemented by the suggested further physical analysis.

The gradually commencing (G) storms have been shown by the Thelliers (1948, 1949), and by Newton and M~lson (1954), to be those that most clearly manifest the 27-day recurrence tendency. This implies that they are mainly caused by long continuing solar streams, from the emitting regions named M regions by Barrels. The suddenly commencing (ssc) storms may be ascribed to the onset of limited solar clouds, such as we suppose are ejected during solar flares: or to continuing M streams that happen to have rather sharp boundaries. The pa,%icles of M streams may well travel more slowly than those in the clouds that produce ssc storms. This would allow longer time for thermal motions, and perhaps also turbulence, to make the lateral boundaries of the stream diffuse. As the solar rotation brings first the leading edge of the stream, and then the body of the stream, in line with the Earth, this diffuseness could make the storm beginning gradual. The outlying part would be halted by the geomagnetic field at a distance of very many Ear th radii. As the body of the stream came to impinge on the field, the surface of the hollow would shrink in- wards, and the DCF currents and field could grow gradually. For similar reasons the entry of the particles into the auroral zones, and the onset of the DP par t of the field, would be more gradual.

On the 7)ther hand in a cloud of gas the particles that had been ejected with the greatest outward speed would travel on beyond their more ta rdy com- panions. This would tend to make the sudden commencement rather more sharp (within a duration of order 100 seconds), although of course the number density would decrease for the particles with the most extreme speeds.

In using the DCE, DP and DR analysis to classify a magnetic storm, it is necessary to examine the records of the storms from a considerable number of observatories well distributed over the Earth. One or two particular examples will be given (w 12) to illustrate the method as now conceived. In selecting and examining these storms I have had the advantage of the collaboration of S.-I. Akasofu, by or with whom detailed studies of these and other storms will later be published.

Naturally the intensity of each part of the D field, DCF, DP and DR can be separately assessed. In doing so, it is necessary to have regard to the presence of the S (and L) parts of the recorded variations. As regards DP, the number of the main impulses can be determined, and the duration of each, examining also the locations, extent and movements of the associated auroral electrojets: and also the degree of DP enhancement in the equatorial electrojet. The location of the electrojets should be examined in relation to the simultaneous situ- ation of the geomagnetic axis relative to the Sun and the sunlit hemisphere.

As regards DR, the time of its apparent onset, and the r~pidity or otherwise of its growth and decay, need consideration. In some storms DCF may include double or multiple ssc's. These may correspond to sudden enhancements of a continuing stream, or to the onset of a new stream after the first or earlier streams had ceased to flow on to the Earth. This may happen while the field variations due to DP and DR are still active, perhaps through changes in the Van Allen belts, set in motion by the initial stream.


S. Chapman

12. PARTICULAR MAGNETIC STORMS*)

According to the arguments given by one of us in the above sections, a pre- liminary at tempt at a physical analysis of several magnetic s torms has been made. Although our studies are still tentative, some of the conclusions already

ii" J U L Y 11-t2 J U L Y 15 -16

+ 2 0 0 ....................... . .......... ,...

+ 1 0 0

O S A N J U A N -I00[

- 2 0 0

- 3 0 0 I 1 I I I I I I 1 I I I | I I t I 1 I I I ] I I I 1 1 ~ 1 I I I I 1 I I i i t i i i I i i I

o ~ . . . .

' ~ T A M A N R A S S E T ~ ~ " ' : : " " " " '"'"~;>~"---~ ~ - 2 0 0

- 4 0 0

} I I | I i I I ; I I I I I I l l I L I 1 J I I

+200 ~ - - - ~ . . . . . . . . . . . . . . . �9 . . . . ~ ~ ~ v ~ . . . . . . . . . . . . . . . . . - . , , . . . . . . . . . . . . . . . . . . . . . . .

0 M'BOUR - 2 0 0

" 1 I | I I I | I I I 1 I 1 I 1 | I ~ l I I I I 1 [

+ 2 O O ~ . ] + IOO

O

- I O O - E L S A B E T H V l L L E

- 2 0 0 F--

- 50o -

I 1 1 1 l �9 I I t + 1 0 0 - , , J , , , , , , , , , J , , , , , , , , , , _" , , ,

0 - r " - " - - - - , - , _~ L ~ . . . . . . . . . .

- 2 0 0

-300

, . , ",, 1 I ! 1 1 I I I I I I I I I i I

14 IB 2 2 2 6 l O G . M . ' [ 8 12 16 2 0 2 4 4 G.M.T.

J u l y 1 1 - 1 2 , 1 9 5 9 - - J u l y 1 5 - 1 6 , 1 9 5 9

........ J u l y 1 3 - 1 4 , 1 . 9 5 9 ........... J u l y 1 3 - 1 4 , 1 9 5 9

Fig. 1. Horizontal component magmetograms from low latitudc stations, for a highly contrasted pair of magnetic disturbances; Left., July, 11- ] 2, 1959; Right July 15--16, 1959. Dotted lines indicate the quiet day curves of July 13--14, just between the above two

s torrt-ls.

*) by S.-I. Akasohl and S. Chapman.

40 Studia geoph, et geod. S (1961)

Magnetic Storm.~: Their Geometrical and .~t~ysical Analysis, and their Classi/ication

obtained are here given. They will be further developed after s tudy oI more data.

For convenience and for clear presentation, some records of two pairs of highly contrasted magnetic storms are presented and discussed together.

~' JULY It-J2 .,I- 100 /

[ p,,, . . . . . . . . . :--.. .... o

- I 0 0 ! M U N T I N L U P A - 2 0 0

- 3 0 0

- 4 0 0

- 5 0 0

l i l t 1 1 I J I l I I I I | i l l I I I | I - 6 0 0 + I 0 0

0 ....... ~ : : f K A K I O K A

- I 0 0

- 2 0 0 '

- 3 0 0

JULY 15-16

f - ~ - v

I . l l l l ] l l i l [ i l l l [ l i i | i l I i l l i f l l | i l l [ l | i l l i l l l l

o ~ ' ~ - ~ . . . . . . . . . . . . . . . ~ U L =":'-":::":":: " ........... _i001. HONOLULU " ~ , , -zool- - \ ~ , . , _ _ . . . . - ~ -

+ , o o ~ ~ . ~ . ~ . . . . . . . . ~ . ~ .......................................................................... .~.

, , . . . . . 3 0 0 1 1 . . , . i i i . ~ , i , i , , , i i , = , , . . . . . A .T 14 18 22 2 6 IOG.M.T. 8 12 16 ZO ~*1. ' ~ , / .

- - Ju ly 11-12,1959 Ju ly 15-16, 1959

. . . . . . . Ju ly 13ol4 , 1959 . . . . . . . . . Ju ly 1 5 - 1 4 , 1959

Fig . 2. S a m e as F i g . [.

(1) The s t o r m s of J u l y 11--12/1.959 a n d J u l y 15--16/1959.

These two IGC storms began at 16h26 m G~'IT Ju ly l t , and 08h03 = GMT July 15, 1959. Several remarkable differences are immediately evident from the magnetograms. Table 1 gives brief particulars of the two storms relative to DCF (and ssc), DP and DR (Fig. 1, 2). All the numbers given are still prelimi- nary. Definite values will be ~ven in a later paper. The ranges of the ssc's and


S. Chapman

,_.r

w

u.l _1 ...I o

~ 0

8

b-

I t !

0

i i o

,(

-I

,~.,.., I -

o c ~ ~.~

,-S.~

0~.~

~2

~q

e4 ~

o , . . ~ o I

N~ m . 4 ~

0 ~ ' 0 0 0 0 0 0 0 0 0 0 0 0

41 .~_ ~- i i

the DCF's may indicate the relative energies of the solar flux and its changes during the two storms (w 6). I t seems likely that the rate of energy f lux on Ju ly 11--12 was at least as much as on Ju ly 15--16, and perhaps more.

There was no clear DP on July 11-- 12. On the other hand there were at least t en large DP pulses on Ju ly 15--16. Some of them decreased H by as much as 1700y.

The two storms also differed greatly with respect to their DR part (Fig. 1, 2). We cannot yet give definite values of LIH, but the value was about 10 times larger on July 15-- 16 than on Ju ly 11-- 12.

These notable DR differences between the two storms may not correspond to a difference of solar flux of energy. The Ju ly 11--12 s t ream was the more energetic, according to the evidencc of the ssc and the DC2'; these in fact are classed as great. I t is notable tha t although the DCF was so large, and continued as long as 7 hours, yet there was no definite DP, and no clear cut DR. I t must be emphasized tha t this was not a very exceptional case. Hence we infer tha t a r a t h e r u n i f o r m a n d c o n s i d e r a b l e s o l a r c o r p u s c u l a r f l u x m a y n o t a l w a y s p r o d u c e e i t h e r DP or DR (Fig. 3).

I t may be questioned whether the DCF on Ju ly 15--16 un- derwent much change in the course of time. I t is almost im- possible to infer its magnitude after the DR began. However, for example, at 08h30 ~ on Ju ly 15, there was no appreciable change in the DCF. Neverthe- less a large DP began quite

42 Studla geoph, e t geod. 5 (1~61)

Maffnet iv Sto~rms. ' T h e i r Geometrical and P hys i ca l A n a l y s i s , and their Cla,~si/ication

suddenly at that time, and the DR also started not long afterwards. Fur- thermore, the development of the DR seems to be closely related to tha t of the DP pulses.

Tab le l

J u l y 1 i - - 12/1959 J u l y 15- - 16/1959

ssc 16h26 ~ (G3IT 08h03 ~, (GMT) H ~ 90 y (Guam) H ~ 70 u (Guam)

D C F prolonged; it c o n t i n u e d for 7 hou r s soon ove rwhe lmed by H ~ 60 "( D R a n d D P

D P no def in i te deve l opmen t ; ve ry weak began ear ly (30 rain. a f t e r the ssc); m a n y pu l se s ove r a per iod of 16 h o u r s

H = 1700 y (College)

D R began la te (7 hou r s a f te r the sse). began ear ly (30 rain. a f t e r the ssc). H ~ 5 0 y H ~ - 4 0 0 y

m a x i m u m : i1 h o u r s a f t e r the sec

Table 2

S e p t e m b e r 13/1957 S e p t e m b e r 29/1957

sge

_JcL 00h47 m (GMT)

H obscu red by D P (50 y)

soon o v e r w h e l m e d b y D R a n d DI"

D P Success ive pu l ses began a t 01hl0 m, 02h50 m, 06h35 m, 08h35 m, 1 lh30 m The f i rs t pu l se soon followed the sse

D R { H ~ 400 y began ~ r l y i

[

00h16 m (GMT)

pro longed over 13 hou r s

success ive pulses began a t 13h20 m, 14h10 m, 17h10 m, 21h40 m

The first fair ly large pulse (13h20 m) appear - ed a b o u t 13 hour s a f t e r t he ssc

began la te H N 300 y

The above contrasted examples seem to suggest some difference in the struc- ture of the solar corpuscular stream between the two occasions. This physical analysis calls for accurate values of the separate parts of the field, .DCF (and ssc), DR and DP, at different points on the Earth. They can be obtained only from numerous magnetograms for a worldwide set of observatories.

Studia geoph, et geod. 5 (1961) ~3

S. C~aztnan

o o o o o o , db

- pr)

.a

0

0 ~

~>

r~

g ~

~ g

0 "~ ~

8 Z Od ' ~

m ~

0 ~

~2

~N e o

m

b o

01 9 #J

: : , :: i , ~ r , , r ~ l L ' j ~ ] , ~ 0 0 0 0

o �9

B J o ,j]

!\J o I ~ ~ - ~ [ . .

"'1 ~- - - ~ ' ~ I ~ ~ ] i ~ ~ I '~ TL/~" C') 0 0 0

0 ~- 0 0 0

r~ q )

0 0 0 0 0

4:4 S t u d i a g e o p h , e t g e o d . S (1961}

Magns t i c Stor~>,~: The i r Geometrical and Phys ica l Ana lys i s , and their Classi / icat /on

~o

o

_:o

z

-s LtJ C~

F-

LL~

PO

_ b

b

o

b o~

w

~ J

0 0 o o d _ 0

13

xt.

0 0 0 0 0

I E

o

rc~

5 X $

(D . /

"~ . . 0

~ ~" "~ .~

, ~ - ~ o

~ - ~

e~Z ~

~ m N ~

�9 ~.~ ~,

�9 "t ~

e l ~ o

N N o I

. ~ g"-

S t u d l a g e o p h , e t g e o d . S (1961) 4 5

S. Chal>man

The ssc's are often enhanced along the magnetic dip equator on the dayside hemisphere (Fig. 4, 5). Hence ssc's from equatorial stations should be carefully used in estimating the solar flux energy (cf. Akasofu and Chapman, Geophys. inst. Publ.).

~ o n g the clip equator Sq is also large, and may somewhat obscure the development of .DR (see the Guam magnetograms, July 11-- 12). To determine the intensity, extent and location of the DP pulses, magnetograms from many observatories are needed, well distributed along the auroral zones.

7

I

DP 0110 0250 0655 0835 1130 i .{ ~ i t

sc o o " 4 ~ . ~ o ~ 2~

? ~ , ' , f , , , , ,,2 , , , , , ,8 , , , ? " T

OP 1320 1410 1710 2140

SC O0 h 16 m Main 13 h 20 m

H

SEPT. 29, 1957 "~ 2667'

Fig. 6. Horizontal corhponent rnagnetograms from Hermanus Observatory, near Cape- town, _Africa, for a contrasted pair of magnetic disturbances; upper: September 13, 1957; lower: September 29, 1957. The beginning times of t h e / ) P ' s and of the main phase are

indicated.

(2) S e p t e m b e r 13/1957 and S e p t e m b e r 29/1957.

These two I G u storms are likewise highly contrasted. Table 2 gives some particulars concerning them (Fig. 6).

4:6 Studia geoph, et geod. 5 (1961)

Magnetic Storms: Their Ge(~metrical and Physical Analysis, and their CIassi]ication

Tile energy of solar flux (indicated by DUE) was definitely larger for the earlier storm, but it may be doubted whether the difference was great enough to produce the remarkable differences between the other main features of the

GNE TOGRA MS (H).FEB.I I, 1958

COLLEGE(ALASKA)

~'~'~l

"V/VBYRD STATION

t

PRU H ON i I~ (CZECHOSLOVAK IA)

~ II 12 13 14 1,5 16 17 GMT

Fig. 7. Horizontal component magnetograms from College (Alaska), Prflhonice (Czecho- slovakia), Honolulu (Hawaii) and Byrd (Antarctica). The different force scales are in-

dicated by ~he length of the arrows on the left; they correspond to 500~.

studia geoph, et geod. 5 (1961) J~7

S. Chapman

two storms. I t is certain that in the later case (September 29) the solar flux continued from the sac until t3h20% because over that interval the auroral zone was intermittently disturbed by small D P putses (not shown in Table 2). This example clearly indicates the close relationship between the development of D R and of the D P pulses.

HIGH LATITUDE

LOW LATITUDE

GM. LAT. COllEGE 64.'7N

PRUHONICE 49.9 N

HONOLULU 21.0 N

GUAM 5. 9 N

BYRD 70. 5 S

HCHAN6E DP 1SOOt V

540~

4 9 0 ~ J

6 1 0 ~

I 0 0 0 ~

DR Fig. 8. S c h e m a t i c p r e s e n t a t i o n of d i f f e r e n t t y p e s of H va r i a - t ion , in low a n d h i g h geomag-

/ ne t i c l a t i t udes , f o r t he s t o r m of F e b r u a r y 11, 1958. N o t e the cha- r a c t e r i s t i c d i f f e r e n c e s b e t w e e n the m a g n e t o g r a r m s for h i g h a n d low l a t i t u d e s t a t i o n s . The diffe-

r / r e n t H r anges and. the f ields t h a t m a i n l y c o n t r i b u t e to t h e m are i n d i c a t e d b e l o w the g raph .

(3) The s t o r m of F e b r u a r y 11, 1958

This example is given separately, because the intensity exceeds anything observed in the last decade. Ulffortunately, about 71~~ ,'o of the observatories missed par t of the record, because of its rapid and abnormally large changes. Hence the material for the s tudy of this remarkable storm is less adequate than in the ease of the other IGY/IGC storms (Fig. 7, 8). The ssc occurred at 01h24 m, and another large sac (about 400,f) occurred later. (Any 8sc or si af ter the first ssc may be regarded as a change of D C F . )

There were two powerful pulses after these sac's, but the large D C F associated with the second ssc immediately overwhelmed them. The D R at Guam was as large as 600,(.

R e c e i v e d 28. 3. 1960 Reviewer: J. Bouglca

4 8 Studia geoph, et geod. 5 (1961)

.~Iaffnetic Storm~: Their Geometrical and Physical Analysis, and their Classi/ication

Re/e~'gTl,ce8

[1] W. G. A d a m s : Comparison of simultaneous magnetic disturbances a t several observatories. Phil. Trans. Lend. (A), 283, 131--140 (1892). See also C h a p m a n and B a r t e l s : Geomagnetism, p. 273.

[2] S. A k a s o f u : The ring current and. the outer atmosphere. J . Geophys. Res., 65, 535--543 (1960).

[3] S. A k a s o f u : Largo scale aurora motions and polar magnetic disturbances. J. Atmosph. Terr. Phys., 19, 10--25 (1960).

[4] R. L. A r n o l d y , R. A. H o f f m a n , J. R. W i n c k l e r : Ob~rva t ions of tile Van Allen radiation regions during August and September 1959, Par t I. J. Geophys. Res., 65, 1361-- 1376 (1960).

[5] J . B a r t e l s : Twenty-seven day recurrences in terrestrial magnetism and the rotation of the Sun. Terr. ~ag. , 27, 57--79, (1922). See also C h a p m a n and B a r r e l s : Geomagmetism, p. 410.

[6] K. R. B i r k e l a n d : The Norwegian Polaris Expedit ion 1902--1903, I, I I . H. Ashe- houg & Co., Christiana (1908, 1913).

[7] S. C h a p m a n : Theories of the aurora polaris. Ann. de Gdophys., 8, 205--225 (1952). [8] S. C h a p m a n : Regular motions in the ionosphere: Electric and magnetic relation-

ships. Submitted to Bulletin of Meteor., (1960). [9] S. C h a p m a n , V. C. A. F o r r a r o : A new theory of magnetic storms. Tort. Mag., 36,

77--97 (1931). A new theory of m .agnetic storms, Par t I -- The initial phase (Con- tinued). Terr. Mag., 36, 171--185 (1931). The theory of the first phase of a gee- magnetic storm. Terr. Mat., 45, 245--268 (1940). The geomagnetic ring-current: I -- i ~ radial stability. Tort. Mat., 46, 1--6 (1941).

[10] J. A. Des s lo r , E. N. 15arker: l=[ydromagnetic theory of geomagnetic storms. J . Gee- phys. Res., 64, 2239--2252 (1959).

[11] V. C. A. F e r r a r o : Ca the theory of the first phase of a geomagnetic storm: A new illustrative calculation based on an idealized (plane not cylindrical) model field distribution. J . Geophys. Res., 57, 15--49 (1952).

[12] N. ~ e r l o f s o n : See I-I. A l f v 6 n : On the theory of magnetic storms and aurorae. Tellus, 10, 104--116 (1958), p. 107.

[13] D. F . . ~ I a r t y n : The theory of magrtetic storms and auroras. Nature, 167, 92--94 (1951).

[14] H. W. N e w t o n , A. S. ~ I i l son : The distribution of great and small geomagnetic storms in the sunspot cycle. J . Geophys. Res., 59, 203--214 (1954).

[15] T. O g u t i : Notes on the morphology of SC. Rep. Ion. Res. Japan, 10, 81--90 (1956). [16] T. O b a y a s h i , J . A. J a c o b s : Sudden commencements of magnetic storms and

atmospheric dynamo action. J. Geophys. Res., 62, 589--616 (1957). [17] A. S c h m i d t : Erdmagnetismus. EazyklopS, dio der Mathem. Wiss., VI, 265--396

(1917). [18] ~. F. S i n g e r : A new model of magnetic storms and aurorae. Trans. Amer. Geophys.

Un., 3.~, 175--190 (1957). [19] C. S t b r m e r : Sur los trajectories des corpuseules 616ctris6s dans l'ospace sons Faction

du m~g~6~isme terrestre avec application aux aurores bor6ales..dxch. Sci. Phys. Nat. Gea6ve, 32, 117--123 (1911); 33, 51--69 (1912). The polar auroras, Oxford Univ. Press (1955).

[20] M. S u g i u r a , S. C h a p m a n : A study of the morphology of magnetic storms; weak, moderate and great storms. Abh. d. Akad. d. "W ss. G6ttingen, Math.-Phys. Klasse.

[21] E. T h e l l i e r a n d ':~rne.: Sur une diff6reuce essentielle entre les orages magndtiques, ence qui concerne la r6currence de 27 ]ours. Paris, C.-R. Acad. Sci., 227, 1044-- 1046 (1948). Sur la variation, au cottr du cycle solaire, de la periodo et de l 'ampleur de la rgcurrence des orates maga6tiques. Paris, C.-R. Acad. Sci., 228, 715--721 (1949).

[22] B. A. Tpo~rli~a~, M. Me,a~nKo~a: 0 xapatr m~Tep~a:mx I~o.'~eSam~fi y6~,rBa- ~onl~rx r~o nep~o/ty (I0--i ce~.), B 3:Tet~Tpo,~arlr~TliOM no,~e 3eM:IH ~ llx r C ~B~le- H r ~ t ~ nepxr~ef~ aT~mad~epe. ~o~r AH CCCP, 128, 917--920 (1959).

[23] J. A. V a n A l l e n , C. E. M c I l w a i n , G. H. L u d w i g : Radia t ion observations with Satellite 1958 e. J. Geophys. Res., 64,271 --286 (1959).

[24] ft. A. Van A l l e n , L. A. F r a n k : Survey of radiation around the Ear th to a rad ia l distance of 107,400 kin. Nature, 183, 430--434 (1959).

[251 C. H. Bep~oB, A. E. X y ~ a ~ o ~ , II. B. B~y,~oB, IO. H. JIora~e~t: I[3y~emte :',e.~- Yioro goplIyCI-ly.~IgpHoro H~z~yqem~ ~ KOCMW[ecKi.~X :Iy,~efi np~t rlO:IeTe ~oe,~m,~ecKofi pa- KeTIa. ~r[ol~.~ta~r,t AH CCCP, 125, 304--307 (1959).


S. Chapman

[26] J. 1~. W i n c k l e r , L. P e t e r s o n , R. A r n o l d y , 1%. H o f f m a n : X-rays from visible aurora~ at Minneapolis. Phys. 1%ev., 110, 1221--1231 (1958).

[27] J. I~. W i n c k l e r , L. P e t e r s o n , 1~. H o f f r n a n , R. A r n o l d y : Auroral X-rays, cosmic rays, and related phenomen~ d~ring the storm of February 10--11, 1958. 5. Geophys. Res., 64, 597--610 (1959).

Pe3~oMe

M A F H H T H b I E B Y P H : t l X F E O M E T P H H E C H H 1 7 [

H ( D H 3 H q E C H H I : I A H A . J I H 3 , H H J I A C C H d ) H H A I ~ H H

S X-DI~E ~ CIL4~PM.A~ Feo~uau'~ec~.u~ l~l~cmumym, J:~usepcumem A,~.uc~u u 06cepeamopun ab~co~ux sb~com,

Boy,*Oep , Ho~opaOo

B CTaTI:,e O6'B~CHeHBI 30CIIOBHMX TglIa BapHau~Ifi FeoMaFIIHTHOrO IIOJIA: BeI(oBMe, TpaH- CIleHTHIaIe ilpaur~,2Bnr~e H TpaHcHeHTHMe ffenpasaasHMe, H3 HOTOp~X Haa6oaee nMpas~Tea~- ~ reo,~ara~TH~e 6ypm Ha oc~one coo6pamem~fi o paa.nomeHz~ ~ B3a~M~OM ~eI~ICTBHIi noaefi M, D, S ~ L 6~,~o no~po6Eo upoaHa.n~a~posaao noae D n Te~eH~ reoMar~aTHofi 6ypm ~ a a~aaH3a 6M~o acno~s3osaHo 350 reoMarH~w~x nO3MymeH~fi aan~caBBHx Ha 19 o6cep~aTop~mx s nep~o/le OW 1902 ;XO 1945 ro;xa.

HocTyr~no 28. 3. 1960

50 Studia geoph, et geod. 5 (1981)

Documents

Magnetic storms: Their geometrical and physical analysis, and their classification