BOHUMILA BEDNAROVA-NOVAKOVA/CZECHOSLOVAKIAN WORK ON THE ORIGIN OF GEOMAGNETIC STORM/ROLE OF SOLAR FILAMENTS/PREDICTION OF SOLAR FLARES

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• Collection: FOIA Collection
• Document Number (FOIA) /ESDN (CREST): 06131746
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• Document Creation Date: December 28, 2022
• Document Release Date: September 25, 2017
• Case Number: F-2015-01649
• Publication Date: December 24, 1964

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CENTRAL INTELLIGENCE AGENCY
This material contains information affecting the National Defense of the United States within the meaning of the Espionage Laws, Title
18, U.S.C. Secs, 793 and 794, the transmission or revelation of which in any manner to an unauthorized person is prohibited by la
C-0-N-F-I-D-E-N-T-I-A-L
COUNTRY Czechoslovakia
SUBJECT
REPORT NO.
Bohumila Bednafova-Novakova/CzechoslovakianDATE DISTR.
Work on the Origin of Geomagnetic Storms/
Role of Solar Filaments/Prediction of NO. PAGES 2
Solar Flares
REFERENCES
DATE OF.
INFO. December 1964 and earlierl
PLACIE&
DATE ACQ. - December 1964 and earlier
24 December 1964
(b)(3
THIS IS UNEVALUATED INFORMATION
(b)(3
(b)(3;
59 pge ar e, in English, entitled, "On
Geomagnetic Storms," co-authored by
Vaclav Bucha, Jaroslav Halenka, and Majmir
the Probiems or rne urigiu ul
Bohumila Bednarova-Novakova,
Konecnv, all of the Czechoslovakian
Academy of Science's Geophysical
Institute, Prague
UNCLASSIFIED]
1.
Above listed on file item is one of the more complete works in a long
series of booklets, pamphlets,
articles, letters, etc, authored by herself
and other members of the institute,
over the years on the subject
(b)(3)
of solar magnetic storms and
predictability by the examination of filaments. [All these items are
available on loan]
2.
With some of her statements, such as that dlaiming solar flares are
essentially uuimportant to the
study of geomagnetic storms, Madam Bednarove
complete disagreement.
Other aspects of the work, however,
are convincing enough there should be some US investigations
(b)(3)
along similar lines.
3.
Much US work has been done on
solar filaments, but not as Bednarova has, on
their use as a means of predicting
solar geomagnetic activity.
(b)(3)
some prediction is possible by her method,
thWOX
unconvinced of the extent she claims for it. Like so many of the other
(b)(3)
Soviet and East European scientists, she accepts a few agreeable phenomena
as "proof" of her thesis and thus tends to build much of her later work
on a poor foundation. Never the less, her work has continued to become
more precise and complex over the years; she continues in her efforts, and
now claims a prediction time of several days.
4.
Several recent US filament studies
have failed to 'support Bednarova's
claims. In support of her reply,
was based on filaments in general,
however, the US work
(b)(3),
and lacked the sophisticated selection
5
4
of type that she states is necessary. Although there is little support for
5.
(b)(3),
her system in this country, there may be some sound
basis for her claim and that-it-baritt-ttrtner-examination.
3
2
1
C -0-N -F -I -D-E -N -T-I -A -L
'STATE
I ARMY
I NAVY
S �NO
IR
coN1.1"."1,l).'l\INO DISSEM ABROAD
The dissemination of this document is limited civilian employees and active duty nriPary personnel within the Intelligence comport
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in accordance with paragraph 8_of DCID ill, it may be rel ,sed to those components of the departments and agencir.s of the U. S. Government
participating in the .production of National intelligence. IT Sl ill NOT BE DISSEMINATED To CONTRACTORS. ft shall not be disseminated to 4)
tion1 or personnel, Including consultants, under a contractucr .elationship to the U.S. GovernmenNwitheut the written permission of th� originator.
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)0 NOT TY1iLABOVE LINE
00 NOT TYPE ABOVE LINE ,
0
-2-
$. tednereve hes worked in this field for many years now, seemingly with
increasing prominence, fail, however, to find any indication..
of USSR, or other, direction- or support to back up space communication
or man.in-space,progrems.
5
4
3
2
CONTROLLED DISSEM
-end-
NO DISSEM ABROAD
(b)(3)
(b)(3)
ife*
34C-Th.
4
3
2
m4.1gmura�muot.
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PRACE GEOFYSIKALNIHO OSTAVU ESKOSLOVENSKE AKADEMIE VED
TPYT(13I rE0413H3WIECKOF0 PIHCTLITYTA IlEXOCJIOBAU,KOPI AKAAEMHI4
HAYK
TRAVAUX DE L'INSTITUT GEOPHYSIQUE DE L'ACADEMIE
TCIOCOSLOVAQUE DES SCIENCES
No 192
GEOFYSIKALNi SBORNIK 1963
ON THE PROBLEMS OF THE ORIGIN
OF GEOMAGNETIC STORMS
Bohumila Bednafova-Novalova, Vaclav Bucha, Jaroslav Halenka,
Mojmir KoneenY
Geophysical Institute Czechosl. Acad. Sc., Prague
Contents
Introduction
408
I. Events on the Sun
409
1) Sunspots
411
2) Flares
4.13
3) Filaments (prominences)
414
4) Relations between spots, flares and filaments
415
II. Conditions in interplanetary space and exosphere
416
III. Geomagnetic activity
418
1) Time variations of geomagnetic field
418
2) Classification of geomagnetic storms
421
3) Attempt at new classification of sc-storms
423
IV. On the question of the mechanism of geomagnetic storm development
428
I) Basic classification of geomagnetic storm
428
2) Types of geomagnetic storms from aspect of their geographic expression
429
3) On the theory of the causes and origin of geomagnetic storms
431
V. Connection between processes on the Sun and geomagnetic activity
437
1) Solar activity � Phases of development of active centre
437
2) Geomagnetic activity and sunspots
438
3) The question of the geoactivity of flares
441
4) Filaments and corona � their geoactive effects
446
5) Deductions � On the problem of geomagnetic storm prognosis
454
Conclusion
456
407
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INTRODUCTION
The study of questions concerning the origin of geomagnetic storms represents a
very topical problem of a wide scientific and practical range; for this reason relatively
great attention is at present devoted to it. The aim of the present paper, apart from
some new conclusions, is to give tt comprehensive interpretation of the results obtained
by us when studying the connection between geomagnetic and solar activity and to
contribute towards an evaluation of the knowledge obtained hitherto in this field of
research. In investigating the relations between the two effects the paper starts out
with a brief discussion of solar events and the mechanism of geomagnetic storms,
which is included in order to clarify the dependences given. The paper tries to point
out the complexity of the problems solved.
Geomagnetic storms, which according to the character of their expression can be
divided into several groups, are caused essentially by processes taking place on the
Sun. A neutral cloud of ions and electrons of solar origin approaches the region of the
Earth, where it is influenced by the latter's magnetic field. At such a mutual effect of
the dynamic and magnetic factors an electrical current system is induced in the cloud.
This leads to the compression of the Earth's magnetic field and thus to the origin of the
first phase of a geomagnetic storm. As is seen, a relatively complicated mechanism
marks the actual process of the formation of a storm. This mechanism can be divided
into several partial stages as a function of the place and the conditions in which these
processes take place.
The basic source of all geomagnetic disturbances of the external field are processes
taking place on the solar surface and in the corona. It is well known that the active
regions on the Sun exhibit relatively strong magnetic fields which influence the move-
ments of glowing solar matter on the surface and in the neighbourhood of the Sun.
The forms of such flow and the movement of matter differ and also the expressions of
such events, as observed on the solar disc, have a quite definitely defined character.
An important object of present-day research is to clarify which of these processes may
be geoactive.
It is thus important to study the composition of solar corpuscular streams, and
particularly to determine whether they can maintain and carry with them part of the
magnetic field from the Sun. The study of this question may contribute towards
explaining the fact that some magnetic storms are not followed by a storm of cosmic.
radiation.
Another open question is how corpuscular streams behave in the space between the
Sun and the Earth before they reach the region of the geomagnetic field and to what
extent they are braked by the interplanetary gas.
Another field of research deals with the space in the neighbourhood of the Earth,
where complex processes take place due to the motion of particles in the magnetic
field. The hydromagnetic processes obviously taking place here are certainly strongly
dependent on the conditions and physical composition of the outer atmosphere. The
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questions of the laws of interaction between magnetic fields and fluid-motion are also
very important despite the fact that many new results have been obtained by observa-
tions using satellites.
The basic material for studying geomagnetic storms are their expressions as recor-
ded at magnetic observatories. If, however, we wish to explain their physical causes
and the influences to which they are subject during their formation and to contribute
towards explaining the mechanism of their formation and their prognoses, the results
of studying processes taking place on the Sun, which are the primary cause of geo-
magnetic storms, must be taken into consideration.
The above-mentioned partial problems show the whole sequence of data from the
initial impulse on the Sun up to the expression of the geomagnetic storm on the
Earth's surface.
The present paper also aims at contributing, at least along basic lines, towards
explaining some of the above questions, particularly as regards processes taking place
at the formation of geoactive processes on the Sun and as regards the classification of
magnetic storms and the relations between solar and geomagnetic phenomena.
Questions of the magnetic fields on the Sun and the hydrodynamic processes taking
place there are discussed. An evaluation is made of the different events on the Sun
with regard to whether they may be considered as sources of disturbances in the geo-
magnetic field. Chapter II contains some brief notes on the conditions in inter-
planetary space.
It is well known that a whole series of geomagnetic disturbances occur which differ
from one another. This question of the classification of storms is dealt with in Chap.
Chapter IV gives some data on processes taking place at the interaction of corpus-
cular streams with the geomagnetic field.
In Chap. V the authors sum up their results of studying the dependence of magnetic
storms on solar activity. An evaluation is also made of the results obtained up to now
from which some interesting conclusions are drawn as to the causes of magnetic
disturbances.
The conclusion contains an evaluation of present-day knowledge as well as descri-
bing the main tasks to be solved in the immediate future.
I. EVENTS ON SUN
The processes, which take place on the solar surface and which are connected with
the interaction of the motion .of glowing matter and the magnetic fields are very
complicated and heterogeneous. However, one can find among them a series of proces-
ses exhibiting a certain system in their occurrence and form. It is found that magnetic
fields on the Sun have a great influence on the production of different solar formations.
Although it cannot yet be deduced whether parts of the magnetic fields are transferred
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from the Sun to the Earth with the corpuscular stream and whether they influence the
magnetic field of the Earth directly, in any case these fields play a role in the ejection of
particles from the solar region. The importance of studying them is therefore obvious.
Analogously as for the Earth, there exists a total magnetic field of the Sun which can
be modelled by means of dipoles. Although the intensity found for the total field
reaches relatively small values compared with the magnetic fields accompanying some
other solar effects, its dimensions show its decisive influence on the formation of a
corona of so-called minimum type. If regions of strong local fields occur then they
greatly disturb the total field in the neighbourhood of the Sun, which, due to their high
intensity, loses its dipolar character.
From the geoactive point of view the formations occurring in connection with sun-
spots as well as the spots themselves are important; the effects are included under the
concept of a centre of activity. The development of such a centre is governed by certain
laws while the lifetime of the phenomena which occur is not the same. The whole cycle
of development of such a region has been described in detail in [1].
We are interested in those formations about which it can be assumed that they
might be the causes of geomagnetic storms. Opinions held hitherto on this question
have varied a lot and have been far from giving a clear answer. They can be divided
into three groups:
a) The causes of geomagnetic storms have been ascribed to the occurrence of spots
on the Sun. Earlier statistical comparisons, which paid no attention to other processes
occurring in the spot regions, showed a certain connection particularly for average
values from annual intervals; however, the degree of correlation between the two
effects decreases with decreasing length of the intervals. At shorter intervals the con-
nection between the two effects can no longer be proved [2]. A more detailed analysis
of the solar situation during the occurrence of spots showed that certain connections
are apparent between geomagnetic activity and spots of large dimensions. They
� depend to a great extent also on the mutual arrangement of the spots. The correlation
improves [3] if spots with a high flare activity are used in the analysis.
b) For this reason relatively great attention was paid to the occurrence of flares.
Certain relations have been found between the occurrence of geomagnetic storms and
strong flares. At present flares are regarded in the world as the source of geornagneti-
cally effective corpuscular streams. However, as regards medium and weak flares, no
laws were found. For this reason increased attention is paid in this paper to the
question of the geoactivity of flares.
c) It has also been shown [4] that the occurrence of filaments in the neighbourhood
of the central meridian (CM) tesults, in approximately 3 to 5 days, in a magnetic
disturbance. One might deduce from this that filaments are the source of corpuscular
radiation. Coronal rays above 'filaments were regarded as an even more likely cause
of storms [5]. A profounder set of laws was found on the basis of a detailed investi-
gation into filaments and their relation to the coronal formations [6,7]. The question
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from the Sun to the Earth with the corpuscular stream and whether they influence the
magnetic field of the Earth directly, in any case these fields play a role in the ejection of
particles from the solar region. The importance of studying them is therefore obvious.
Analogously as for the Earth, there exists a total magnetic field of the Sun which can
be modelled by means of dipoles. Although the intensity found for the total field
reaches relatively small values compared with the magnetic fields accompanying some
other solar effects, its dimensions show its decisive influence on the formation of a
corona of so-called minimum type. If regions of strong local fields occur then they
greatly disturb the total field in the neighbourhood of the Sun, which, due to their high
intensity, loses its dipolar character.
From the geoactive point of view the formations occurring in connection with sun-
spots as well as the spots themselves are important; the effects are included under the
concept of a centre of activity. The development of such a centre is governed by certain
laws while the lifetime of the phenomena which occur is not the same. The whole cycle
of development of such a region has been described in detail in [I].
We are interested in those formations about which it can be assumed that they
might be the causes of geomagnetic storms. Opinions held hitherto on this question
have varied a lot and have been far from giving a clear answer. They can be divided
into three groups:
a) The causes of geomagnetic storms have been ascribed to the occurrence of spots
on the Sun. Earlier statistical comparisons, which paid no attention to other processes
occurring in the spot regions, showed a certain connection particularly for average
values from annual intervals; however, the degree of correlation between the two
effects decreases with decreasing length of the intervals. At shorter intervals the con-
nection between the two effects can no longer be proved [2]. A more detailed analysis
of the solar situation during the occurrence of spots showed that certain connections
are apparent between geomagnetic activity and spots of large dimensions. They
depend to a great extent also on the mutual arrangement of the spots. The correlation
improves [3] if spots with a high flare activity are used in the analysis.
b) For this reason relatively great attention was paid to the occurrence of flares.
Certain relations have been found between the occurrence of geomagnetic storms and
strong flares. At present flares are regarded in the world as the source of geomagneti-
cally effective corpuscular streams. However, as regards medium and weak flares, no
laws we re found. For this reason increased attention is paid in this paper to the
question of the geoactivity of flares.
c) It has also been shown [4] that the occurrence of filaments in the neighbourhood
of the central meridian (CM) tesults, in approximately 3 to 5 days, in a magnetic
disturbance. One might deduce from .this that filaments are the source of corpuscular
radiation. Coronal rays above filaments were regarded as an even more likely cause
of storms [5]. A profounder set of laws was found on the basis of a detailed investi-
gation into filaments and their relation to the coronal formations [6, 7]. The question
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of the causes of geomagnetic storms has still not been convincingly explained, how-
ever. As is clear from the above, there are considerable differences in opinion as to the
identification of the actual sources of geoactive corpuscular radiation.
Let us now deal in greater detail with the most important solar phenomena from the
point or view of the processes which take place during them and with the possible
mechanism of their origin.
1) Sunspots
It is well known that sunspots have a very strong field, attaining an intensity up to
4500 Oe, compared with the total field of the Sun. It can therefore be assumed that
this property plays a considerable role in the equilibrium of sunspots. The mecha-
nical forces appearing during such phenomena are balanced by magnetic pressures.
The magnetic flux passing through the sunspot region can be expressed by the rela-
tion [8]
(1)
where a is the surface element, H the magnetic field. It is seen that a change in flux
takes place in approximately the same way as the formation of a sunspot region. We
can therefore assume [9] that the field already existed in the deeper parts below the
surface of the Sun before the spot be-
came visible and that it is brought to
the surface by the action of some me-
chanism. This is confirmed by the relati-
vely long-term existence of solar centres
of activity while the sunspots character-
izing the time maximum of the field
have a much shorter life. In the interior
of the Sun, on the assumption of strong
convection, torsional oscillations may
be produced. As a consequence of the
uneven rotation of the Sun certain parts
of the mass may be exposed to oscil-
lations in longitude and latitude; they
begin to get near to the surface of the
Sun and cause considerable distortion
of the lines of force (Fig. I). The pre-condition for this process is a relatively high
degree of magnetic rigidity. For .a non-uniformly rotating Sun, having a magnetic
field, one may consider that it has lines of force frozen into its matter. Its field can
be constant on the assumption that it is symmetrical around the axis of rotation.
Fig. 1. Distortion of magnetic lines of force near
to solar surface at approach of torsion wave to
equator.
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According to the law of isorotation [10] it holds that
(2) OH/at = (H . grad) v (v. grad) H
where H is the magnetic field, v the velocity of motion of the mass.
In cylindrical coordinates R, 0, z. where R is the distance from the axis of rotation,
0 the corresponding angle and z the distance from the equatorial plane, the above
equation can be resolved into components. Let co be the angular velocity so that v =
= RP). If the stationary state of rotation is disturbed as a result of the azimuthal
removal of part of a body, the disturbance is equivalent to a torsional magneto-
hydrodynamic wave propagated along the lines of force. Let the motion be defined by
the component of the undisturbed angular
�� e� velocity coo and the component co' as a result
�
� �
� of the disturbance. Analogously, let the field
% 0
� % � �
�
� e H be composed of the undisturbed component
� I e
e e' %% Ho and the disturbance field h. Then we obtain
� � / �
��������
� � t e�.--��� � (3) Oho/at = R(Ho . grad) co' .
� � t / �
�11111
�515
.11
/ /
/
/
II
II
'II
II'
II I
I I I
III
Fig. 2. Hypothetical distribution of mag-
netic lines of force at their exit from
spots on surface of Sun (vertical cross-
section of spot).
assumption that the disturbance field
In the component 0 of the equation of motion
there then appears only the electromagnetic
force p[j x Ft] so that this component re-
duces to
(4) 47cgR2(0a/at) = p(H . grad) Rho.
The permeability 12, about which it is assumed
that it is equal to one, is usually left in the
expressions to facilitate transformation.
Expressions (3) and (4) form important re-
lations in the theory( of magnetohydro-
dynamic waves. They can be used on the
h is much larger than the field Ho and thus the
torsional oscillations may form a large azimuthal field h from the small field Ho in the
meridional planes [9]. Strong convection may then cause a decrease in angular velo-
city in the interior of the Sun. This fact then causes the torsional magnetohydro-
dynamic wave to propagate along the lines of force in the direction of the surface
(Fig. 1). It may be considered that this torsional wave proceeds against the equator. If
it gets close to the surface the lines of force there form a band around the Sun. On
penetration to the surface two regions with reversed magnetic polarity may then be
formed; in one the lines of force intersect the surface in the outwards direction and in
the other they return inwards. These regions can then be regarded as a pair of sun-
spots with reverse magnetic polarity.
Due to the high values of the magnetic field in the spots the magnetic pressure
(�1-12/8tc) here reaches relatively high values of the order of 1.6 x 105 dyne/cm2. This
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magnitude causes the mass in the regions around the spots to be pressed back and the
lines of force lose their original vertical direction. They are detained in the sub-surface
layers and above the surface, as .is seen from Fig. 2.
Due to the relatively'strong magnetic fields in the spots and in their immediate
neighbourhood solar matter can hardly be released outside the region of the Sun;
the movements of the mass here are governed by their magnetohydrodynamic laws.
Spots can therefore hardly be regarded as a direct source of geomagnetic distur-
bances.
2) Flares
Flares appearing as short-term sudden effects in the neighbourhood of sunspots are
fundamentally characterized by a strong light increase in part of the floccular field and
not by the ejection of matter. In a period of strong solar activity flares occur very fre-
quently, of the order of once in two hours. They do not usually appear at distances
larger than 100 000 km from a group of spots but always inside a facular region. It is
often observed that in a period of flare occurrence existing filaments change or even
disappear, new filaments and surges are formed even at large distances from the flare.
Sometimes, of course, the filaments closely neighbouring a flare remain without
change. It was found [11, 12] that solar flares appear in the region of zero line of the
magnetic field dividing off the places with opposite magnetic polarity.
Although the temperature of the spots is relatively low much higher temperatures
are found in their neighbourhood during flares. These are very probably eleCtro-
magnetic in origin. During the motion of solar mass in the magnetic field of a spot it
can be assumed that the electrical fields produced here may be the cause of electrical
currents and the latter are then the source of tremendous temperature effects. Their
sudden origin in the form of a light increase may then be apparent as a solar flare.
Large flares are usually conjugate with spots having irregular polarity; in this case
they usually have a complicated shape.
During theoretical considerations an investigation was made into the question of the
formation of a corresponding discharge in ionized gas considered as the probable
physical mechanism of the flare and the connection between flares and the surrounding
formations was studied.
During motion in an electric field the electrons collide with the ions [13]. At such
collisions the fast electrons lose relatively little energy. On the other hand, during their
motion they obtain energy from the electric field present. But with increasing tempe-
rature the number of collisions decreases which leads to a further increase in the energy
of the electrons. For a strong electric field this increase may continue without limi-
tation and there thus occurs an effect analogous to an electric discharge.
Let the mean velocity v, the electric field E of which acts on an electron, be given by
(5)
V = � eE . V,
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where V is the velocity of the electrons passing through the solar mass. Then the
change in energy of the electrons
(6) d We/dt eEV 2m,v( W, �
The second term on the right-hand side represents the energy loss of the electrons on
collision with the ions, where v is the frequency of collision, me and m1 the masses of
the electrons and ions. On certain assumptions, when the electric field is perpendicular
to the magnetic field present, we obtain
:
(7) dWe 2m0v (w w Mie2E2 w
d t mi 2me2ani + We)
where a is a value defining the magnetic field present and n1 gives the number of
collisions. The expression in brackets is negative for large values of W� which may
lead to an unlimited escape of electron energies. It thus follows that the discharge
takes place along the lines of force; this is also obvious from the fact that on motion
across the lines of force the mechanical force it[j x 1-1] would rapidly change the
motion of the mass.
As regards the place of origin, on the one hand we considered the region of zero
fields between the spots and on the other hand we assumed the discharge motion
inside the flare to be along the lines of force of the magnetic fields of the spot, the
shape of which is very irregular at turbulent motions of solar matter. The complexity
of the phenomenon under investigation, however, requires further detailed study.
While flares rise to relatively very low heights above the solar surface, eruptive
surges are often produced in their neighbourhood. These appear as bright short-term
prominences rising to relatively great heights, up to 105 km.
3) Filaments (Prominences)
Filaments appear on the solar surface as relatively, stable formations in the shape of
long dark ribbons. In some opinions, coronal matter condenses in them along the
magnetic lines of force. It can be deduced from this that the stability of the filamen-
tary arch-like shapes is to a great extent influenced by the magnetic fields and the rela-
tively high magnetic rigidity. The density of a filament is approximately 100 times
greater than the surrounding corona; the temperature corresponds to -flo-o [1]. A mag-
netic field acts not only on prominences but also on the corona while there often
exists a close relation between these two formations. A convenient grouping of the
fields may then cause a rise in a certain part of or the whole prominence from the Sun
while, at the same time, part of the corona may be expected to flow out above the
rising prominence [14].
A satisfactory theoretical explanation of the origin of filaments has not yet been
given. At present the existence of filaments is relatively well explained in the theory of
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� 9
magnetic arcs [15]. It is assumed that a filament lies along a line of force of a magnetic
field. The weight of the filament mass is compensated by the forces due to the distor-
tion of the lines of force, defined by the factor K. Then the magnetic pressures can be
converted to the forces K4tH2/8n, which must be equivalent to the expression
(product of density and gravity) if equilibrium is to be ensured. For this it is necessary
that for the corresponding values of g and K there be present a field H of an order
of at least 50 Oe. Such a value H can be quite easily assumed in the neighbourhood of
spots; the long-term duration of the existence of prominences can then be explained
by magnetic rigidity. The mass of a filament sometimes appears as though it
were wedged into a shallow tlepression in the
beam of surrounding lines of force. Such
a favourable grouping of the magnetic field
contributes towards the filament remaining
suspended above the solar surface for a long
time. A solution of the magnetohydrodyna-
mic equation
(8) 0 = � grad p + g + p[j x H]
has already been found as applied to this case,
where p is the pressure, Q the density of
the medium and the term p[j x H] expresses the force of electromagnetic origin [15].
The equation of the corresponding lines of force in a prominence is given in the form
(9)
Fig. 3. Course of magnetic lines of
force according to Menzel's theory.
f = exp [(z � z 0,1 .1.]
where z gives the vertical height, 2, a certain constant. The shape of the lines of force is
seen in Fig. 3.
However, such a theoretical conception expresses the carried prominence only in
rough outlines and isolated from all the suirounding influences; the theory of the
origin of filaments will therefore have to be elaborated further.
The theory of jet streams [16] is based on the assumption that a filament is the
trace of electric currents, analogously as in a discharge tube. It is seen, however, that
with such a mechanism the required stability, which is normal for filaments, cannot be
ensured. For this reason the preceding theory seems more favourable for the explana-
tion.
4) Relations Between Spots, Flares and Filaments
The laws governing the formation of an activity centre and its further development
prove that phenomena occurring during the different phases may be related to and
influence one another. Although the characte'ristic features of the different phenomena
are quite different, as regards their duration, form, temperature and place of occur-
rence, some connections have been found although not always proved. The magnetic
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fields are seen here to have a very strong effect; then, as a function of their grouping,
the partial effects may influence one another. Some scientists even assume that the
magnetic fields are the direct causes of spots, flares and the corona. As regards the
connection between them, it has not yet been decided for certain whether the flares
activate the filament or whether the two pheitomenn are different results of the same
cause (change in magnetic field). Here the influences of structure of the magnetic
field present and not only the mechanical forces obvious1ST play a role.
During activation the filament may also disappear but often, particularly in regions
of strong fields, it reappears in its original form after a short time. In the solar atmo-
sphere there is a connection between the motion of the Mass and the magnetic fields
and current systems. This is very strong in the region of sunspots which have large
magnetic fields. Therefore the corona above the group of spots is also strongly de-
formed by local magnetic fields. Sudden changes in their grouping may then result
in the deformation of the corona.
It follows from the above that all the events in the activity centres are fundamen-
tally influenced by the occurrence of magnetic fields and their relatively strong effect
on the corona and coronal formations. Particular attention must therefore be devoted
to these questions.
II. CONDITIONS IN INTERPLANETARY SPACE AND EXOSPHERE
An important factor in the propagation of corpuscular streams after their ejection
from the solar region is the space between the Earth and the Sun, the physical proper-
ties of which may to a great extent influence the behaviour of a moving cloud of cor-
puscular particles. Definite conclusions have not been reached in determining the
density and temperature of interplanetary mass. It is assumed that the density is
approximately 103 particles/cm3.
Different models have been proposed for the interplanetary magnetic field. While
earlier the field was regarded as negligible, it has been found that in this space there
exist regions with a rapid flow of plasma, obviously moving in different directions
[17]. Many scientists assume that the magnetic field is produced here and that it is
maintained by the ejection of parts of the magnetic field of the Sun, caught on the
corpuscular radiation from the active solar regions. The value of the interplanetary
magnetic field is approximately 2.5 x 10 Oe. Fresh data along these lines are pro-
vided by investigations into the paths of cosmic rays which are influenced and guided
by this field. It can be assumed that there exists a relatively continuous transition
between the geomagnetic and the interplanetary magnetic fields.
A great contribution towards explaining the conditions in interplanetary space and
the exosphere has been made bY. material obtained by means of satellites and cosmic
rockets. The discovery of two radiation belts (van Allen) [18] surrounding the Earth,
at distances from 700 km to 60 000 km from the Earth, in which the very intense ra-
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diation of high-energy particles plays a role, has meant the finding of a further impor-
tant link in the chain of events beginning with activity on the Sun and ending with a
geomagnetic storm. The charged particles are caught by the magnetic field of the
Earth. From the equatorial regions they move along the lines of force towards the
poles and cause an increase in magnetic intenaity. M a result of the vertical compo-
nent of the geomagnetic field the motion and oscillation of the particles about the
lines of force is damped. The inhomogeneous geomagnetic field causes the particles to
move in the longitudinal directions on the surface of the level, forming two ring-
shaped regions of maximum radiation intensity (Fig. 4).
Fig. 4. Distribution of radiation (van Allen) belts.
The composition of the particles is not the same in the two radiation belts. In the
outer belt the energy of the electrons fluctuates between 40 keV and 5 MeV, while for
protons it reaches a maximum of 200 keV. On the other hand, the energy in the inner
belt is quite different; for electrons it reaches a maximum value of 600 keV while for
protons it has a much higher value (from 10 to 200 MeV).
The density of the radiation belts is not always the same. Solar geoactivity apparently
causes an increase in the concentration of particles in the belts; however, calculation
shows that the lifetime of protons of the inner belt is limited to a maximum of a few
weeks. The outer belt would also disappear in a short time (a few hours) if it were not
for the effect of a certain source of particles and the mechanism working inside the
magnetic field which keeps the particles in its domain although they no longer have a
high energy.
There are relatively few data available on the character of interplanetary space and
the exosphere so that conclusions as to the conditions reigning there are far from
being complete. A further study of the phenomena, particularly in radiation belts,
could contribute towards explaining the conditions necessary for the motion and
behaviour of high-energy particles.
27 Geofysikalni sbornik 1963
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III. GEOMAGNETIC ACTIVITY
I) Time Variations of Geomagnetic Field
It is already quite clear that the basic cause of geomagnetic activity is solar radia-
tion. Since geomagnetic storms are only one, although the most pronounced, form
of the set of time variations of the geomagnetic field which must be taken into consi-
deration when investigating their connection with solar phenomena, it will be expe-
dient to make a few brief remarks of a broader aspect on the time variations of the
geomagnetic field in general. On the other hand, the solar radiation itself represents
a wide sphere of fundamentally different wave and corpuscular components so that
one can quite obviously expect different effects and mechanisms of expression, and
this is actually the case.
If we disregard the secular variation of the geomagnetic field, which is fundamen-
tally given by the processes taking place under specific conditions deep in the body
of the Earth, and is thus outside our sphere of interest, all the other time variations
are conditioned directly or indirectly by solar radiation. This conditional state may be
understood as "static" if a certain time variation of the geomagnetic field is excited
just by the mere existence, more or less permanent and constant, of the appropriate
component of solar radiation, or as "dynamic" if the time variation is excited only at
sudden and substantial increases in the corresponding components of solar radiation.
A typical example of "static" conditions is the variation of the geomagnetic field on
quiet days Sq, and from the sphere of "dynamically" conditioned variations, a geo-
magnetic storm. These examples concern direct conditions. The purest form of varia-
tions from the sphere of indirect conditions is the variation caused by tidal influences
of the Moon � lunar variation L.
On the basis of a detailed analysis of the above types of variations we proposed the
scheme given in Tab. I where the most important variations and processes in the
geomagnetic field are drawn up, taking into consideration the character of solar radia-
tion.
Before analyzing it, however, a few remarks must be made on solar radiation. The
geomagnetically effective parts, particularly of the short-wave component of solar
radiation (X-rays and ultra-violet region) as well as of the corpuscular component
(electrically charged particles with energy up to an order of 105 eV), are already quite
well known. It should merely be emphasized that in the corpuscular component a strict
distinction should be made between geomagnetically effective radiation and other
geoactive radiation (the solar component of cosmic radiation with particles having an
energy of the order of lir eV). Here there are deviations both at emission from the Sun
and during interaction with the geomagnetic field: on the one hand, one cannot deduce
from the emission of one kind of radiation the simultaneous emission of another kind,
and, on the other hand, the interaction of geomagnetically effective corpuscular radi-
ation with the geomagnetic field can be understood as a hydromagnetic process while
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-the penetration of the solar component of cosmic radiation through the geomagnetic
field can be interpreted by Stormer's theory [19] (Fig. 5).
We shall not take into consideration below the time variations and processes in the
geomagnetic field which are subject to wave radiations and which in their mechanism
and results lie outside our sphere of interest.
Magnetic rigidity, V
105 106 107 108
Liar flare
1"=1011(n=107
8m- nk
101
101�
do.
106- 70%q0
Interplanetary
100-1000 krnisl
I 04 -Thermal particles Solar corpuscles Auroral partici
40g 4010 1,011
Integral Spectrum of Interplanetary Particles
Geomagnetic cut off latitude
/O.
102-
10
ste'
10
e'
401 402 403
Solar cosmic rays
�11
Proton
Polar Cap blackouts
120 100 80 60 .40 .20 km
et Pen' ration height (Proton)
104 165 106 107 168 109
kinetic energy, eV
Cosmic rays
1.010 1011
Fig. 5. Survey of basic types and characteristics of corpuscular radiation in space between Sun and
Earth (after [19]).
As regards the classification of the time variations of the geomagnetic field subject to
corpuscular radiation*) in Tab. I, mention should be made of the following:
Geomagnetic storms: The classification is quite obvious. These very pronounced
disturbances, some of the characteristics of which will be dealt with in greater detail
presently (Chap. IV), are, however, practically always accompanied by the following
variations:
Sudden impulses: These appear as small changes in the geomagnetic field. Their
classification is clear as long as the impulses can be interpreted (after [20]) as a certain
"more moderate" analogy to sudden commencements of geomagnetic storms ssc. This
is probably the interaction between the more pronounced density inhomogeneities in a
constant inflow of charged particles froiri',the Sun ("solar wind") and the Earth's
*) In the following text corpuscular radiation always means geomagnetically effective solar
corpuscular radiation.
27*
419.
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Table I
Plot of dependence of basic variations and events in geomagnetic field on solar radiation (inside square
corresponds to corpuscular component of geomagnetically effective solar radiation)
Condition
"Statical"
"Dynamical"
direct
variations Sq
sudden
impulses
solar flare
effects
Sc and g
storms,
bays
indirect
pulsations
pc
variations L
bays,
pulsations
Pt
/
/
/
/
magnetosphere. From the point of view of solar events this interpretation can be
accepted since a number of processes in the solar chromosphere and corona can be
mentioned which might excite the inhomogeneities; these are particularly changes in
the floccular fields, small flares, surges and changes in the structure of filaments.
Pulsations: In this field of small changes with periods of the order of 1� 100 sec one
can consider two classifications. Apart from the well-known conceptions that the cause
of pulsations are hydromagnetic oscillations of the plasmatic medium of the Earth's
magnetosphere, excited by the interaction of the solar wind with the surface of the
magnetosphere [21], we can also take into consideration the conception that in some
cases the occurrence of pulsations is facilitated by the increase in conductivity of the
ionosphere at a bay disturbance [22]. As regards solar causes, for the excitation of
oscillations one must probably again assume density inhomogeneities in the solar
wind and thus also similar causes as in the case of sudden impulses. We have, however,
preliminarily pointed out some specific features, apparent in the fact that day-type
pulsations pc [23] exhibited a tendency to more frequent occurrence after the passage
of active solar regions with flare activity through the central solar meridian while
pulsations of the night type pt shoWed a tendency to greater occurrence after the pass.
age of regions with probably "quieter" emission of corpuscular radiation [24].
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Bays: With these disturbances of a regional character we are also forced to make a
double classification. The direct condition is obvious, particularly for those bays
which actually form some geomagnetic storms and disturbances with a gradual com-
mencement (g-storms) and it also follows from the possibility of the prognoses of such
bays on the basis of the character of the solar situation (see Chap. V). Other bays,
particularly those which substantially participate in the daily variation of geomagnetic
activity with maximum in the evening hours local time [25], lead rather to the
conception that in periods of increased inflow of corpuscular radiation, the surplus of
particles caught in the Earth's magnetosphere penetrate to the region of polar zones
[26].
2) Classification of Geomagnetic Storms
When classifying geomagnetic storms, necessary inter alia for a more detailed
research of their dependence on solar activity, one can use the quantitative and mor-
phological features of the storms. A quantitative classification makes use of both the
course of the geomagnetic storm found directly and that expressed by means of a sui-
table index of geomagnetic activity.
In the first case the scheme in Tab. Ha is� commonly used. The classification is in
relation to the energy of the geomagnetic storm, the boundaries are obviously purely
conventional and here the well-known dependence of the geomagnetic activity on the
geomagnetic latitude is clear. In the second case the K-index is used. The scheme,
whose boundaries are also conventional, is given in Tab. lib.
Table II
Quantitative classification of geomagnetic storms
a
AH (y)
Storm
Max. K
Storm
300
large
8 � 9
s
severe
H (y) maximum amplitude of horizontal component of geomagnetic field during storm,
max . K maximum three-hour index K during storm.
From the point of view of solar influences it should be emphasized in connection
with the above classification that here there is no simple dependence of the severity
of storms on the importance of visible expressions of solar activity, which come into
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Bays: With these disturbances of a regional character we are also forced to make a
double classification. The direct condition is obvious, particularly for those bays
which actually form some geomagnetic storms and disturbances with a gradual com-
mencement (g-storms) and it also follows from the possibility of the prognoses of such
bays on the basis of the character of the solar situation (see Chap. V). Other bays,
particularly those which substantially participate in the daily variation of geomagnetic
activity with maximum in the evening hours local time [25], lead rather to the
conception that in periods of increased inflow of corpuscular radiation, the surplus of
'particles caught in the Earth's magnetosphere penetrate to the region of polar zones
[26].
2) Classification of Geomagnetic Storms
When classifying geomagnetic storms, necessary inter alia for a more detailed
research of their dependence on solar activity, one can use the quantitative and mor-
phological features of the storms. A quantitative classification makes use of both the
course of the geomagnetic storm found directly and that expressed by means of a sui-
table index of geomagnetic activity.
In the first case the scheme in Tab. ha is commonly used. The classification is in
relation to the energy of the geomagnetic storm, the boundaries are obviously purely
conventional and here the well-known dependence of the geomagnetic activity on the
geomagnetic latitude is clear. In the second case the K-index is used. The scheme,
whose boundaries are also conventional, is given in Tab, lib.
Table II
Quantitative classification of geomagnetic storms
a
4H (y)
Storm
Max. K
Storm
300
large
8-9
s
severe
4H (y) maximum amplitude of horizontal component of geomagnetic field during storm,
max. K maximum three-hour index K during storm.
From the point of view of solar influences it, should be emphasized in connection
with the above classification that here there is no simple dependence of the severity
of storms on the importance of visible expressions of solar activity, which come into
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consideration as sources of corpuscular radiation. It is often observed that from the
point of view of solar activity insignificant events are followed by important geo-
magnetic storms and, vice versa, some very important expressions of solar activity
remain without a response in the geomagnetic field, (An interpretation of this effect
is given in Chap. V.) It seems that much better agreement can be obtained from the
quantitative aspect if solar radio outbursts are also taken into consideration [28, 29].
From the morphological aspect geomagnetic storms are commonly classified ac-
cording to the time sharpness of the onset of a storm and are divided into two types:
storms with sudden commencement (sc-storms) and storms with a gradual commen-
cement (g-storms). It can be expected that these two types differ primarily in the
magnitude of the density gradient of the particles in the front of the corpuscular
stream or even at the side of the stream if the Earth meets a stream which has already
lasted for some time. Differences in velocities cannot play such a role here nor do
our results show them to be so important as is usually deduced (Chap. V).
From the point of view of solar influences the situation in this method of morpho-
logical classification of geomagnetic storms is much clearer than in the preceding case.
It follows from the above that sc-storms are preceded by sudden changes in the solar
situation connected with the short-term emission of corpuscular radiation or a short-
term favourable direction of the emitted corpuscular radiation. On the other hand,
g-storms occur after slow changes in the solar situation, accompanied by long-term
emissions of corpuscular radiation.
The classification based on the dependence of the character of geomagnetic distur-
bances on the geomagnetic latitude can also be regarded as a certain type of morpho-
logical classification corresponding in a heightened degree to the physical mechanism
of the origin of geomagnetic storms as a whole [30]. It is seen that in the belt of low
latitudes, up to about 45�, the disturbance takes place synphasically on large regions
of the Earth's surface (S-type), in the middle and upper latitudes roughly between 45�
to 700 the disturbances may be different even at places only a few hundred km away
from one another (L-type), and finally in the polar regions, above 70�, disturbances
take place on disturbed days more or less permanently and often occur also on days
which are geomagnetically quiet in other belts (P-type).
The dependence of the type structure of a storm on its intensity is important. Ac-
cording to [30] geomagnetic storms with K max 7-9 consist of disturbances of the
type S, L and P, have a pronounced storm variation Ds, and begin suddenly. On the
other hand storms with Kt, max 3 � 6 consist only of L and P type disturbances, no D�
variations are seen and they begin with a gradual commencement.
It is possible that the relation between the intensities of S and L type disturbances,
together with the possible latitude displacements of the boundary in the 45� latitude, is
one of the causes of the occurrence of different types of geomagnetic storms for an
otherwise special morphological classification, the results of which will now be men-
tioned.
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3) Attempt at New Classification of Sc-storms
The gradual refinement of conceptions as to the connection between solar and geo-
magnetic activity has made it necessary, and also possible, to solve other special
problems. One such problem, also of practical importance for forecasting geomag-
netic activity, is the question whether some morphological peculiarities in the course
of different geomagnetic storms can be at least partly derived from the morphological
peculiarities of solar situations during the emission of the corresponding corpuscular
stream. The results would also contribute towards determining to what extent the
specific properties of the different corpuscular streams assumed to be given by the
different character of the solar
situation, where they were emit- 100
ted, are preserved, i.e. to deter-
mining the possible smoothing
effect of the medium along the 10
path of the corpuscular stream.
The investigations made so far
along these lines, the results of
which will be given below (details
will be published later), represent
10
the first step in a broader attempt
at a new classification of geo-
magnetic storms taking into con- -100
sideration the character of the
24 h
solar situation in question. Fig. 6. Average time dependence of horizontal com-
ponent of geomagnetic field for set of storms used in
The records of 90 geomagnetic
experiment on new classification of sc-storms. Vertical
sc-storms on standard magneto- axis: Hd- Hq (y).
grams from the geomagnetic
observatory in Prahonice (1 = 14�33', = +49�59', A = 97.5�, di = +50.1�)
were used for the classification. The typical course of a storm, obtained as the
average of all the cases by the usual method of the displacement of the epochs
of storm commencements (storm variation D�), is shown in Fig. 6. After a detailed
evaluation of the different courses of geomagnetic storms as regards similarity and
deviations from the typical course, the whole set of storms could be reliably divided
into a number of special types according to exactly defined simple criteria. Here, for
the sake of brevity, we give only the plots of the most pronounced representatives of
the different types (Fig. 7) instead of the definitions used in the classification.
Type analysis showed that the majority of geomagnetic storms of the set in question
has the expected "two-phase" course, both phases of which can be modified quite
differently. It is interesting, however, that apart from this a not insignificant part of
the set exhibits a definitely "one-phase" course, also differently modified. The small
remainder is formed by some storms of a more complicated character which obviously
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1
10.11957 1
VP
i
)
,
0
�....
0
sm.
100
10
21. IX.1957 4 P
-10
-100
24h
SSC
100
10
-10
100
-10
-100
24h
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l6..1958 4
Vo P
I
/
24h
)
_
24
29/1k 195.7
2V
100
/0
-10
12 h
-100
SSC
Fig. 7. Selected examples of basic
types defined in experiment at new
classification of sr-storms. Right-
hand top corner of sub-graphs
gives date of origin of storm, order
number of three-hour interval in
which ssc occurred and notation of
type. Vertical axis: Ha-11q(y).
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originated by the overlapping of two or more disturbances, as is also indicated by the
length of their duration. The statistics of the occurrence of the different main types
is given in Tab. III.
In order to decide whether the deviations of the different storm courses from the
typical course cannot be caused inter alia also by the different time of day at which the
storm occurred, the material was classified into partial sets according to the three-
hour period in which the storm started.
The average storm courses of these partial sets, obtained by displacing the epochs,
are on the whole similar (Fig. 8), which indicates that the possible influence of local
time is very small. This is also supported, as was to be expected, by the random distri-
bution of the points in Fig. 9, where all the investigated storms are plotted taking into
0
-30
-60
-30
-60
0
-30
-6
0
-30
-6
Fig
hor
field
int
occ
hor
'
,
�I
I
-I
(
�
:
I
-
.
*
1
i
-5 ssc 5 10 15 20 25
30
i
. 8. Average time dependences of
-30
izontal component of geomagnetic
I for partial sets of storms, divided
-60
.1
r three-hour intervals in which ssc
urred. Vertical axis: Hd� ii,. (6,
. . . . . 1
i
426
axis.
. ssc
ime
pass
rn
-a ssc
10 15 20 25
0
0
0
0
0
9
0
0
30
0
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Table III
Statistics of occurrence of different main types of geomagnetic storms
Type
Number
%
Total
number
VP
OP
PP
V
36
15
2
1
40
17
2
1
54
60
0
P
VO
8
18
4
9
20
4
30
- 33
more
complicated
6
7
6
7
Oh
0 VP
� 0
to PP
OP
+ P
VO
0 V
0 more complicated
�
12
�
Fig. 9. Polar diagram of occurrence of geomagnetic storms used in attempt at new classification
taking into consideration type of storm, moment of ssc and magnitude of maximum amplitude H.
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consideration the type of storm, the instant of sudden commencement and the magni-
tude of the maximum amplitude of the horizontal component of the geomagnetic
field during the storm.
On the other hand, if the occurrence of the different types is investigated separately,
the P and 0 one-phase types show a tendency to occur only at a certain time of day
(Fig. 10). This is also a proof that in the above classification not only possible local
disturbing influences but also causes on a world-wide scale may play a part and that
the classification of storms also has physical significance.
fl
Fig. 10. Polar diagram of occurrence of one-phase geomagnetic storms a) type P. b) type 0, taking
into consideration moment of ssc and magnitude of maximum amplitude H.
IV. ON THE QUESTION OF THE MECHANISM OF GEOMAGNETIC STORM
DEVELOPMENT
The classification of phenomena occurring within the framework of geomagnetic
activity has shown that storms represent a very pronounced group of disturbances. In
order to be able to make use of the laws governing the phases of storms for
studying the connection between solar and geomagnetic activity, the most fundamen-
tal of them should be pointed out here. At the same time one must not forget a brief
definition of the different types of storms from the point of view of structure and
geographical expression together with their theoretical conceptions.
I) Basic Classification of Storms
Geomagnetic storms are distinguished by several pronounced features. If we study
their time dependence (Fig. 11), it can be included in the general characteristics, of
storms [2]. These are:
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a) Sudden commencement, which is characterized by a relatively rapid growth in
the magnitude of the horizontal component of the geomagnetic field, especially in low
latitudes. The value of this increase is on an average around 30 y and increases towards
the equatorial region, where it attains maximum values. The rise time fluctuates around
2 minutes. However, the occurrence of a sudden commencement is not a rule for all
storms. With so-called sc-storms it is observed all over the world but its magnitude
varies from place to place. The sc also reaches higher values in the auroral zone on the
illuminated side. At present the microstructure of the commencements of storms is the
object of interest in a number of papers [31, 32].
08 10 12 14 16 18 20 22 24 02
26 X.1961
Fig. 11. Total time dependence of geomagnetic storm.
05 air
2g. x. t961
b) The initial phase of a storm is the interval lasting for approximately 2 to 8 hours
after the sudden commencement. It is characterized by the fact that the H component
maintains approximately its initial undisturbed value, slightly increased compared
with the period before the storm.
c) The main phase is marked by a considerable decrease in the horizontal compon-
ent compared with the initial undisturbed field. After reaching minimum the. H
component gradually returns but it is covered by strong storminess of the whole
process; for a large part of this period, usually lasting 12 � 24 hours, there are large
positive and negative changes which reach several hundred y.
d) The return phase, as the last part of storm activity, is seen as a further gradual
return of the H intensity to the original undisturbed value and a gradual quietening of
activity (decrease in amplitudes of positive and negative changes). They last approxi-
mately 1-3 days while in the second part there is only a gradual return.
2) Types of Geomagnetic Storms from Aspect of their Geographic
Expression
The records of the time dependence of the geomagnetic field confirm that geomag-
netic storms can be divided into two basic types according to the laws governing their
expression. The first group consists of world storms, which are accompanied by a
general decrease (to a smaller extent an increase) in intensity of the geomagnetic field
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simultaneously over the whole Earth, both in the polar and in the equatorial regions.
The second type are so-called polar storms or disturbances occurring both as negative
and positive forms. Both types of storm are excited by the action of corpuscular
radiation.
a) World storms are disturbances of the geomagnetic field of maximum intensity,
where the fluctuation of the elements reaches values of up to thousands of 7. They take
place over a period of several days. The main changes during a storm occur to a great
TO THE SUN
Fig. 12. System of streams produced in E-layer which formally explains field distribution during
geomagnetic disturbance.
extent simultaneously and similarly over the whole surface but of course the total
dependence is disturbed by disturbances of a local character, particularly in higher lati-
tudes, where there is also an increase in the amplitudes of irregular fluctuations. A
typical world storm begins with a sudden commencement (sudden sharp increase in
horizontal component � ssc) observed in 1 minute synchronously over the whole sur-
face of the Earth, with maximum amplitude in the equatorial regions. Here, too, the
storms occur in their purest form.
After the sudden commencement the storms then develop in phases as described
above.
The average course of the storm is given by the storm variation 1).� to which three
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components of the disturbance field D contribute; the field is described by the expres-
sion [33]
(11) D = DCF + DP + DR.
The DCF field is excited by the inflow of the corpuscular stream (sudden commence-
ment + initial phase), DP is the disturbance field produced in the polar regions
(sudden fluctuations during main phase) and DR represents the effect of a toroidal
electric current.
b) Polar storms have maximum values not directly in the polar regions but in the
zones of aurorae. This proves the connection between the two phenomena. Polar
storms are characterized by the single occurrence or sequence of several sudden
(increase or decrease) deviations from the undisturbed value, the most pronounced at
the horizontal component. The intensity of the impulses decreases together with the
distance from the polar regions in the direction of the equatorial region. In lower lati-
tudes storms are apparent only in the form of a bay; for this reason they are sometimes
called bay storms. Their annual time distribution has been found to be characterized
by two maxima in periods of the equinox. The daily variation of the disturbances then
exhibits interesting properties in that negative disturbances are produced during the
night in auroral zones and positive disturbances during the day. However, many more
negative disturbances occur than positive ones. In the middle latitudes this circum-
stance is not nearly so obvious.
The relatively rich material obtained for these disturbances permitted the proposal
' of a system of currents originating in the height of the ionospheric layer E [34]
1 (Fig. 12), by means of which the observed field distribution during disturbances can
be formally explained. The currents have a high density and flow along the auroral
zones. While there exists only one current system above the polar regions, in the middle
latitudes two vortices are formed; one runs anti-clockwise on the night and morning
side of the Earth, and the other clockwise on the day and evening side. The absolute
, value of the current can reach up to hundreds of thousands of A.
3) On the Theory of the Causes and Origin
of Geomagnetic Storms
The very complexity and irregularity in the course and other characteristic features
of storm activity indicate that not even the finding of the actual physical conception
of the model, which would satisfactorily explain all the natural phenomena taking
, place during storms, will be easy or without obstacles.
Research hitherto has basically followed two different lines, the difference consisting
mainly in the conception of the properties of interplanetary space and of the charged
particles moving along the Sun-Earth path.
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CL) The first conception is based on the assumption that in interplanetary space there
exists no large magnetic field and that the ionized matter emitted from the Sun is not
magnetic. This assumption is used in many theories starting out from hydromagnetic
equations as well as in the classical theory of Chapman-Ferraro [35], which in addi-
tion assumed the negligible influence of interplanetary gas.
19 The second conception is based on thc opinion that the ionized clouds emitted
from the Sun are magnetized either by the total solar field or by local fields of the
active regions. The particles move with a velocity of 108 cm/sec and the flux is also
electrically polarized; the electric field is of an order of 1� 100 V/cm and is very impor-
tant for the creation of magnetic storms. The theoretical procedure is then based on
a study of the motion of the individual particles.
Difficulties arise in the first group of theories if it is required to explain how a cor-
puscular cloud penetrates into the magnetic field of the Earth; it is equally difficult
to explain the formation of a toroidal current. Also the 27 daily variations of cosmic
radiation are in conflict with the fact that interplanetary space has no magnetic field.
The incorrectness of this opinion was proved by cosmic radiation measurements by
means of satellites. The Forbush decrease in intensity of cosmic rays was recorded at
large distances from the Earth due to the influence of the magnetic field present there,
which is in considerable disagreement with the second conception.
Let us now deal with the basic features of some models which try to explain the
different phases observed during storms. Recently theoretical research has taken into
consideration the latest observational data on the state of interplanetary space and the
exosphere, which has led to more exact physical models.
The starting point for all more recent theoretical models of geomagnetic storms is
the assumption of an electrostatically neutral corpuscular stream propagating from
the Sun to the Earth. However, opinions differ as to the effect of such a stream on the
magnetic field and this has led to the elaboration of different models.
a) The model based on the effect of a dipole magnetic field on the moving conduct-
ing medium [35] assumes that a cylindrically shaped cloud of corpuscular gas with
sharp boundaries approaches the geomagnetic field. If the medium is conductive, then
by its approach to the magnetic field electric currents are induced in it which prevent
the magnetic field from penetrating into the interior of the corpuscular cloud. In
addition mechanical forces of a repulsive character are produced between the dipole
and the conductive medium and try to prevent the cloud from further movement.
Since the conductive medium is not rigid, these forces cause the surface of the cor-
puscular stream to begin to deepen and a cavity to be formed in it. The lines of force
between the Earth and the front of the cavity densify results in an increase in
the horizontal component of the geomagnetic field, observed during the initial phase
of the geomagnetic storm. The increase in the horizontal component 411 at a sudden
commencement, which is related tb the dimensions of the cavity and the flux moment
nmv2, is described by the expression H0/8z3, where Ho is the equatorial value of the
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horizontal component on the surface and z = (111181rE) /6 represents the distance
between the peak of the cavity and the centre of the Earth. Further, the energy E =
= H2/8rc = rimv2, where H is the geomagnetic field in the peak of the cavity, n the
density of the particles, m the mass and v the velocity of the corpuscles. The main
phase, seen as a decrease in the horizontal component, can be explained by the pro-
duction of a closed toroidal electric current around the Earth, flowing in the equato-
rial plane. This current is formed as a consequence of the electric field produced by
volume charges which collect on the evening and morning side of the cavity as a result
of the separation of the charged particles by the geomagnetic field. Only protons are of
importance for the current due to their large gyration radius.
b) The model explaining the origin of geomagnetic storms by the effect of the
electric field of a corpuscular cloud [36] is based on the assumption that the particles
of electrically polarized gas emitted by the Sun carry with them the magnetic field
frozen into a highly conductive medium. When the beam of ionized gas moves an
electric field is produced described by the relation E = � (1/c) [v x H], where v is the
velocity of motion of the beam and H is the field frozen into the beam. When the
flux reaches the Earth's magnetic field and the separation of the positive and negative
particles begins, the influence of the electrons flowing round the Earth in the eastern
direction is seen in the form of a sudden commencement. The motion of particles in a
combined electric and magnetic dipole field consisting of circular motion superposed
on translational motion was calculated. The velocity of particles behaving in this
manner is given by
(12) v = � (4612) [H x {eE � � grad H � m(dvIdt)}]
where kt defines the ratio of the kinetic energy of the particle to the magnetic field.
The motion of particles forms a volume charge in certain regions, which leads to the
creation of toroidal currents. When looking from the north pole the left-handed
current forms a sudden commencement while the creation of the main phase of a
geomagnetic storm is ascribed to the right-handed current (due to the eastern motion
of the electrons).
The interval between the sudden commencement and the main phase of a geomag-
netic storm was not explained by this model. The following model attempts to do
this.
c) The model taking into consideration a shock wave in the origin of geomagnetic
storms is based on the assumption that apart from the corpuscular stream a shock
wave, which has its source in the ejection of particles from the Sun [37], also plays a
role in the storm mechanism. Such a wave contributes to the separation of the charges
and thus also to the causes of currents flowing in the atmosphere and manifest as a
sudden commencement. It follows from the theory of strong shocks that the velocity
of the gas borne along by this wave is only three-quarters of the velocity of the shock
wave. Therefore, the corpuscular stream reaches the Earth with roughly a nine-hour
28 Geofysikalni sbornik 1963
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lag (Fig. 13). The particles of this stream can therefore penetrate into the depths of the
geomagnetic field and thus also into the forbidden Stormer regions since they enter
the field already disturbed by the wave. The particles caught in the geomagnetic field
move primarily along the geomagnetic lines of force but simultaneously they drift
according to their polarity to the east or west while an electric current is produced
which flows in the western direction (main phase). This current gradually decays due
to the absorption of the part-
icles in the Earth's atmosphere,
which also explains the decay
of the geomagnetic storm.
d) The hydromagnetic mo-
del is characterized by the
interaction of solar plasma
with the geomagnetic field
and the method of propagating
the effects towards the Earth.
It is assumed that due to the
influence of the pressure of
solar plasma the Earth's dipole
field is limited by regions up
to a distance of approximately
10 Earth's radii [38], where
the magnetic pressure is al-
ready lower than the pressure
of the solar plasma. When
the plasma suddenly ejected from the Sun collides with the geomagnetic field
processes occur which result in the geomagnetic storm on the Earth's surface.
Fig. 13.
The sharp front of the solar plasma cloud is formed by the influence of the inter-
planetary magnetic field and the gas present there.
The basic hydromagnetic equation defining the relation between the velocity v of the
particles, arriving at the region of the geomagnetic field on sudden ejection from the
Sun, and the intensity of the magnetic field is given in the form [38]
(10) dv/dt = � (P1 + P2 + B212/10) + (BY) BIPO
where P1 gives the pressure of the tenuous plasma in the field B, P2 is the equivalent
pressure of the injected particles and B2/2;20 is the magnetic pressure. The different
phases of the storm can then be ascribed, as has been elaborated in detail, to the
partial expressions of the interaction resulting in the production of pressures propagat-
ing towards the Earth in the form of hydromagnetic waves.
The sudden commencement of a geomagnetic storm is ascribed to the impact of
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solar plasma with the sharp front on the geomagnetic field. This disturbance propa-
gates towards the Earth in the form of a hydromagnetic wave.
The initial phase of a storm is caused by the increase in pressure of the constantly
inflowing solar wind on the magnetic field of the Earth. The main phase is obviously
due to the pressures which are produced in the Earth's magnetic field by the trapped
protons of solar origin. A considerable part of the pressure is caused by the centri-
fugal force of the trapped particles at their oscillation along the lines of force during
passage through the equatorial plane (Fig. 14).
A geomagnetic storm ends with the phase
of decay, which due to its limited duration /
Ns,
requires the quietening of most of the �,
/-
, ,
trapped particles in a period of about one
day. This process corresponds to the me-
,
chanism of charge exchange between the ;
active protons and the neutral atoms of
atmospheric hydrogen.
e) The model of a geomagnetic storm,
which is based on a combination of the
effect of the homogeneous electric field of
the volume charge and the system of irre-
gular fields, aims at explaining the mecha-
nism of the penetration of solar ions into
the geomagnetic field [39]. Existing theories
explaining the origin of geomagnetic
storms by the effects of the corpuscular stream have in most cases not been able to
explain how the particles can penetrate into the Earth's magnetic field. The increase in
the horizontal component (at a sudden commencement) cannot be caused by a to-
roidal current outside the geomagnetic field but by a mechanical force acting on the
electrically conductive gas at a distance of several Earth's radii in the direction of the
Earth. On the other hand, during the main phase the mechanical force acts away
from the Earth. The effect of such a force leads to hydrornagnetic processes in regions
at a distance of several hundred km from the earth due to the moving gas in
the magnetic field. The consequence of such processes is that the lines of force of the
magnetic field, frozen into the conductive medium, are borne away from the Earth
and form an elongated cylindrically shaped formation, "a magnetic tail", on the
unilluminated side of the Earth (Fig. 15). The continuous acceleration of the ions in
this "tail" against the Earth by the electromagnetic forces leads to a total decrease in
the horizontal component of the geomagnetic field � the main phase of the storm.
The theory is based on a study of the motion of two forms of gas� � ion-electron
plasma and neutral atomic gas. The application of such a study shows that at distances
of several hundred km from the Earth's surface the disturbances are transported by
28*
Fig. 14.
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means of the hydromagnetic waves, while in lower regions the dispersion medium
causes the disturbances to be transported by means of diffusion. This model permits
an explanation of some important effects connected with the course of a geomagnetic
storm, including processes in the radiation (Van Allen) belts, counterglow, daily
variations in cosmic rays etc.
Fig. 15.
The principal conceptions of the above models represent a brief survey of the basic
and latest theoretical conceptions as to the conditions necessary for the creation of the
mechanism of geomagnetic storms. The very fact that a series of models exists in
parallel, each of which is physically substantiated in a different way, indicates that it
has not yet been possible to arrive at a completely satisfactory conception which
would be in keeping with the physical nature of storms and would also explain their
partial features and individual pecularities. Greater uniformity could certainly be
achieved by studying other parameters which have not yet been sufficiently investiga-
ted but which might play an important role in the correct physical conception of the
model.
One important way of refining such parameters is indoubtedly a study of the con-
ditions and causes of the emission of solar geoactive corpuscular radiation. In this the
above models differ quite considerably; some do not take the question of the emission
mechanism into consideration at all and others make obviously very simplified as-
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sumptions although it can be expected that the parameters by which the corpuscular
stream enters into interaction with the geomagnetic field will to a great extent be given
by the mechanism of its origin on the Sun. The determination of the correct relations
between solar and geomagnetic activity is a contribution towards finding the most
probable parameters.
V. CONNECTION BETWEEN PROCESSES ON SUN AND GEOMAGNETIC
ACTIVITY
The connection between solar and geomagnetic activity has been known for more
than a century but still no unified conception has been reached as to what is the source
of geoactive corpuscular radiation. Different papers treating the various epochs
of the solar cycle have dealt with all the expressions of solar activity and a definite but
often unsatisfactory connection has been found. For this reason a detailed analysis
of all the expressions of solar activity had to be made and their inter-relation deter-
mined when elaborating a method for the prognosis of geomagnetic storms.
Investigations into active centres consisting of successive expressions of solar acti-
vity have shown that on its passage through the central solar metidian (CMP) one
and the same active region often has different consequences corresponding to its phase
of development, and that the geoactivity (i.e. the following increase in geomagnetic
activity excited by corpuscular radiation) depends on their instantaneous state at the
time of the CMP. It was also found that the connection between active regions and
geomagnetic storms is not a simple affair since it depends on the processes taking
place in their surroundings and on the mutual configuration.
These questions became the object of our investigations. Here we give some of the
most important conclusions with a view to contributing towards a clarification of the
above relations which have been the object of geophysical research for a number of
years. Our attention will successively be paid to all main phenomena occurring in
active centres both as isolated effects and taken complexly.
Since the geoactivity of a solar active centre substantially depends on its phases of
development, let us first deal briefly with the chronological sequence of events on the
Sun from the point of view of their development.
1) Solar Activity � Phases of Development of Active Centre
A
Each active region is preceded by the formation of a local magnetic field. Bright
small facular and floccular fields appear and gradually increase their extent. Then spots
are formed but these accompany the life of the active region for a relatively short time.
They gradually become larger and the magnetic field becomes complex. If the deve-
lopment of the group of spots reaches a certain degree flares and surges begin to occur
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in it and filaments (prominences) appear. The chromospheric structure shows that in
the chromosphere there is a very complex magnetic field which corresponds to a cer-
tain extent to the photospheric field. During flare activity in the active region more
filaments are produced while those already existing here often change their direction
and shape or even disappear (activation of filament). Others are "extracted"
from the region, and straighten if they were previously arc-shaped. Sometimes these
changes occur during flares while at other times this occurs in a broad time interval
around the flare. For the filament to disappear it is not necessary that it be near to a
flare. Distant filaments also often disappear. According to the mechanism explaining
the existence of a filament, which was given in Chap. I, it can be assumed that their
disappearance may occur when the magnetic field which kept them in equilibrium is at
least temporarily compensated. Such compensation occurring in the period of changes
in the magnetic field can be expected rather in those parts of the active region where the
magnetic field strength is lower than that of weaker disturbing fields. It can be admit-
ted [40] that filaments disappear as a consequence of changes in the local magnetic
fields; one cannot, however, neglect the influence of the total field which adds up with
the local fields.
In the next phase the filament moves away from the active region and different basic
configurations can occur. From the behaviour of the free part of the filament we can
deduce that it is under the influence of the magnetic fields of the surrounding spots.
Sometimes the filament may decay [41] or join up with a neighbouring filament.
If so-called spot prominences are produced by the condensation of the coronal
masses on the lines of force of the strong local magnetic fields already formed directly
above the active centre, then the above interpretation of the disappearance of the
filament due to compensation by the field can be applied.
Filaments often last much longer than the period of spot occurrence; they remain in
the floccular field and are gradually shifted to higher heliographic latitudes. Finally, the
floccular field disappears entirely and only the filament remains. Apparently the rota-
tion causes the filament to turn into the approximately parallel direction while the
filaments originally occurring in the spot zones had the meridional direction.
2) Geomagnetic Activity and Sunspots
When investigating the relations between these phenomena it was generally found
that in the same way as the occurrence of sunspots falls into a eleven-year period so
geomagnetic storms are subject to analogous laws. This fact As become the starting
point for many scientists in their search for inter-relations. The average values of the
main characteristics (number, area and relative number) of spots were primarily
compared with different geomagnetic indices. It was found statistically that a few days
after the CMP of the spots there exists a definite probability of the occurrence of
geomagnetic storms. A comparison of the individual cases, however, showed that not
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all spots are followed by geomagnetic storms. Nor was the opinion confirmed that
there exists a direct connection for the largest groups. Such groups are to a great
extent the seats of other expressions of solar activity so that the conception taking into
consideration the geoactivity of spots might probably be more justified. However, not
even in this ease is the connection given between spots and geomagnetic activity satis-
factory.
20-
10-
40-
19 22 25
220-
170,
120-
20-
10-
0 25 28
60-
� � -2�.�
11
10 13 16 1.9 22
Fig. 16. Time dependence of relative number of sunspots R (line with points) and daily sums of
K-index of geomagnetic activity in period a) 19. U.� 17. III. 1952, b) 25. IV.-22. V. 1951.
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A p
Let us now deal in greater detail with the question of whether spots by themselves
can be geoactive. We compared the curves of the daily values of the relative number of
solar spots [43] and the daily sums of the K-indices [44], characterizing the geomag-
netic activity [45]. In a number of cases it was clearly seen that geomagnetic disturb-
ances are produced even in those epochs when spots did not occur on the Sun at all
and, vice versa, there is often a decrease in geomagnetic
activity even at large spot activity. Examples of the
two above cases are plotted in Fig. 16. It is seen from
Fig. 16a that in the epoch of zero relative number (25.
II. to 4.111. 1952) there was an increase in the K-indices.
On the other hand, they decreased around 19. V. 1951
(Fig. 16b) when the relative number was very high.
Such investigations would not in themselves be proof
because the relative number does not take into conside-
ration the position of the spots on the solar disc.
However, due to the conception of the radial propagation of corpuscular radiation one
can expect the distance between the group of spots and the centre of the disc to be the
decisive factor. For this reason we investigated the chosen very quiet, internationally
determined intervals of geomagnetic activity [46] for the years of a fall in solar
activity (1950 to 1953) from the period when the zones of sunspot occur' ence approach
the equator and thus when the individual groups of spots may occur more frequently
in the centre of the disc. A quiet interval can thus be expected when there is no geo-
active source in activity on the Sun. Table IV shows, however, that in 90% of the cases
the quiet intervals in 1950 were preceded by the CMP of sunspot groups [47], which is
a quite convincing proof that spots cannot be geoactive. With the decrease in solar
activity the percentage of quiet intervals preceded by the CMP of sunspot groups also
decreases but this is the obvious consequence of a decrease in the number of sunspot
groups in the direction of the minimum of solar activity. It thus follows that a large
number of sunspot groups is followed by a pronounced decrease in geomagnetic
activity, i.e. these spots cannot be the source of geoactivity.
Comprehensive material was elaborated by the method of superposed epochs during
10-
Fig. 17. Average time depen-
dence of geomagnetic activity
after CMP of groups of spots,
which were not accompanied
by central filament.
440
Table IV
Very quiet intervals
Number of intervals
Year
%
total
with preceding spots
1950
19
17
90
1951
11
8
73
1952
13 ,
7
54
1953
17 '
5
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the 1937 �1958 period in order to reach a definite decision on the question of the
geoactivity of spots. Zero day was taken to be all the CMP of isolated groups of spots
regardless of type, whether with or without flares; these groups were not accompanied
by a filament passing through the centre of the solar disc. Altogether 110 cases were
investigated to find the average course of the geomagnetic activity expressed by the
values of the Ap-index [48] in the critical period after CMP (Fig. 17). It is obvious
that the activity in this period is very low and, moreover,
shows a slight decrease on the + 1 and +2 days. Since
it might be objected that this statistical treatment could
smooth out the possible geoactivity of the most
important sunspot groups, the set of most important
and medium sunspot groups was treated individually.
Not even in these most favourable cases did a geo-
magnetic disturbance occur, as is seen in Fig. 18. These
results showed quite definitely that spots in themselves
cannot be geoactive. The connection between spots
and geomagnetic storms found by some earlier statis-
tical papers can easily be explained by the fact that
the methods used then did not take into account the
occurrence of other expressions of solar activity in
the spot regions.
3) The Question of the Geoactivity
of Flares
Shortly after the discovery of flares the first con-
clusions were drawn that strong flares are connected with
geomagnetic storms [49]. The values they gave for the
velocity of propagation of corpuscular streams are still recognized. Later a statistical
verification was made of the results where it was found that there is a certain dependence
of the geoactivity of flares on the distance from the centre of the solar disc; according
to this the angular aperture of the cone in which the corpuscular rays are emitted from
the flare, would be roughly 90� [3, 50]. As material has accumulated great attention
has been paid to this question in other papers. The results obtained for the direct
connection between flares and geomagnetic storms, however, showed that the cor-
relation is not convincing [51]. The question of why a large number (around 50%) of
flares, even when conveniently situated, do not appear to be geoactive is still unan-
swered. Papers have also appeared which doubt any connection [52� 54]. Sometimes
the geomagnetic disturbance is ascribed to flares occurring on the edge of the disc.
In our work we concentrated on a detailed investigation of the main aspects of
the connection between flares and geomagnetic activity.
Ap
20
10
a
0
10
0
20
10
20
10
0
1
0
4
2
3 d
Fig. 18. Time dependence of
geomagnetic activity after CMP
of four selected largest groups
of spots which were not ac-
companied by central filament.
Date, type and heliographic
latitude at CMP of group of
spots: a) 12.VIII.1940, F, 7�N,
b) 20.VLII. 1940, F, 9�N, c) 14.
IV. 1943, E, 14�S, d) 17. VI.
1958, E, 15�N.
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The material from the IGY period was elaborated statistically using the method of
superposed epochs [55]. We found that even the commonly used statistical methods
produce results which cannot be satisfactorily explained by assuming a direct con-
nection between flares and geomagnetic activity.
An analysis of the results led to the conclusion that the geoactivity of flares, parti-
cularly of those with smaller importance, should be understood as the geoactivity of
the active regions in which these flares occurred. A statistical evaluation was then
made by an analogous method [57] of all flares observed in 1937 to 1956 and con-
tained in the Catalogue of large chromospheric flares [56].
Fig. 19. Average time dependence of geomagnetic activity after flares i = 3, with regard to distance
of flares from CM. Full line � central flare (29�E� 29�W), dashed line � western flare 30�W),
dotted-and-dashed line � eastern flare 30�E).
Figure 19 shows that although medium flares are followed by a pronounced increase
in geomagnetic activity the analogous increases for eastern and western flares are time
displaced so that the maximum for western flares is earlier and that for eastern flares is
later. This fact, together with other proofs, led to the above conclusion that there exists
only an indirect connection between flares and geomagnetic activity. We also found
that even if a direct connection is admitted, the value of the angular aperture is smaller
than 60�.
It is also clear from [57] that the mean value of the time interval between a
flare and the following geomagnetic storms has only formal significance and depends
on the length of the period to which we confine ourselves in ascribing the geomagnetic
storms to the different flares (Fig. 20). This indicates the random distribution of
geomagnetic storms occurring after flares and does not give the typical mean value of
the interval.
Two conceptions of how to. understand the connection between flares and geo-
magnetic storms were proposed for a satisfactory explanation of all the dependences
found statistically:
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. 1) Flare activity in the active region, or any other source of geoactivity of the active
legion in which a large flare occurred, lasts for a long time, during which the active
region may pass through the central meridian. If the conditions for the emission and
direction of a corpuscular stream are fulfilled in this critical position, then this active
region may be followed by an increase in geomagnetic activity with which the flare in
question is not directly connected.
160
140
120
100
80
60
40
20
a
80
70
60
50
40
30
20
10
, � 0
0 10 20 30 40 50 60 700 10 20 30 40 50 60 70 h
Fig. 20. Summation curves for set of time intervals between large flares and following geomagnetic
storms. a) all flares, b) central flares (29�E� 29�W).
2) The increase in chromospheric activity, which was seen inter alia as the occurrence
of a large flare in some active region at a distance from the CM, need not remain
limited only to this active region and its� immediate neighbourhood but can appear
more or less simultaneously in more distant parts of the solar surface. If such an
increase takes place also in the active regions which are just on the CM, then such
regions may be followed by an increase in geomagnetic activity with which the flare
in question is not directly connected.
The above statistical results are in keeping with the individual investigations into the
geoactivity of the different active regions with rich flare activity. Four isolated active
regions were chosen (this means that during their passage over the solar disc practically
no other flare activity occurred on the solar surface) and the results of observing
-flares in them were classified with the course of the geomagnetic activity during
passage over the solar disc [58]. Despite the fact that throughout this time a series of
large flares occurred in the active regions, the geomagnetic activity increased markedly
only in the expected interval after the passage of the active region through the cen-
1#4
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tral meridian (Fig. 21). From this it is clear, inter alia, that the influence of flares
might be seen (if it exists) only in the immediate neighbourhood of the CM; thus
conceptions ascribing geomagnetic storms to flares on the edge of the disc are
quite unjustified.
Previous papers paid particular attention to how flares are reflected in geomagnetic
activity; this means that the zero day in the method of superposed epochs was the day
of occurrence of a flare. A possible connection can be verified, however, in the opposite
direction, i.e. whether an increase in geomagnetic activity is preceded by a flare (zero
day in the method of epoch displacement is the day of increased geomagnetic
activity).
Kp
9
6
3
0
1950 II 14 1.5 16
C MP
40�N 266�
48 19
A20 2
ssc
1
2
22
SSC
3 22 2 2+ 3+ 2 2
2 2 2+
4 25 26 2?
Fig. 21. Time dependence of geomagnetic activity (points) around CMP of active region with
occurrence of strong flares (vertical lines with notation of flare importance).
With this in mind a statistical analysis was made of the solar situations preceding
sudden commencements of geomagnetic storms (ssc), which also contains an elabora-
tion of the occurrences of flares between these commencements in 1957 � 60 [40].
Only those ssc were chosen for which 100% observation of flares was ensured in an
interval of 28 to 38 hours before an ssc. This 10-hour interval was chosen on the basis of
the results of investigations which will be discussed in the next chapter. The investiga-
tions covered flares of all importances from 1 � to 3+, which occurred in + 100 from
the CM. The percentage of the number of cases when no such flare occurred before
a sudden commencement was calculated. Table V shows that a geomagnetic storm.
occurred on an average in 45% of the cases without being preceded by a flare.
Due to the problematical character of the connection between flares and geo-
magnetic activity, which is clear from the statistical papers just discussed, it can be
deduced that the increase in geomagnetic activity observed sometimes after flares could
actually be explained by the geoactivity of other expressions of solar activity occurring
in the active regions together with.flares or possibly the geoactivity of expressions
occurring on the CM synchronously with the flare which is at some distance from the
CM. -
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A partly complex procedure was therefore adopted in investigating the influence of
flares; not only flares but also filaments about whose connection with geomagnetic
activity positive conclusions had been reached (see paragraph 4), were taken into
consideration. The different configurations of flare and filament were thereby con-
sidered. Material was elaborated from 1950 �1959 [59] for which the method of super-
posed epochs was used to determine the average variation of the A p-indices around
Ap
Ap
20-
a
80-
10-
60-
0
20-
...
10-
40-
0
20-
20-
1
�\
10-
-2-1 +1 +2 +3
Fig. 22. Average time dependence of geo-
magnetic activity after occurrence of flare
without presence of filament on centre of
solar disc, taking into consideration distance
of flare from CM, a) max. �450,
b) max. + 20�, c) max. + 100.
o �4 � d
Fig. 23. Average courses of geomagnetic activity
after occurrence of flares (max. + 450 from CM)
in simultaneous presence of filaments.
filament on disc centre on same day as
flare; filament preceded (1-2 days);
� . �. filament followed (1-3 days); � � � one
filament preceded, other followed.'
zero day (all days with the occurrence of a strong flare i = 3 or 3+ at successive
distances of 100, 20�, and 45� from the CM were chosen as zero day), in all 48 cases
without the occurrence of a central filament (i. e. one, of which a certain part would
pass through the centre of the solar disc). It was found (Fig. 22) that after the occur-
rence of flares without the presence of a central filameni. no increase in geomagnetic
Year
Table V
Number of geomagnetic storms not
preceded by any flare
1957
1958
1959
1st half 1960
0/0
30
54
46
50
mean value
45
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activity occurred; on the contrary, a slight decrease is observed. This is proof that there
was no geoactive source in activity at the time in question and therefore the flare itself
is not geoactive.
Quite different results were obtained when zero day was taken to be the day on
which there was a flare at a maximum distance of �45� from the CM but a central
filament occurred, as is dealt with below. On the basis of 23 cases we distinguished
four basic situations as a function of the time configuration of the flare and filament:
a) the passage of the filament through the centre of the disc occurred on days of flare
occurrence, b) the passage of a filament occurred just before a flare (roughly up to
1 � 2 days), c) the passage of a filament
occurred just after a flare (max. 1 to
2 days), d) two filaments passed through
the centre, just before and after a flare.
The method of superposed epochs was
used for all these four situations to obtain
the average courses of the geomagnetic
activity (Fig. 23) from which the following
conclusions can be drawn:
After the simultaneous occurrence of
a flare and a central filament there is
Fig. 24. Average time dependences of geo- a pronounced increase in geomagnetic
magnetic activity after occurrence of flares at
max. distance of �45� from CM a) without
presence of filament on centre of solar disc,
b) in presence of filament on centre of solar disc.
activity. In other cases the increase in
geomagnetic activity is governed by the
passage of the filament through the centre
of the disc so that the maximum of the
increase is time displaced in keeping with the time displacement of the passage of a
filament from that of a flare. The geoactivity of the :opposite solar situations is shown
in Fig. 24.
Apart from this, individual investigations of the same question on a set offlares of
homogeneized importances gave analogous results [60] confirming the fact that flares
are not the direct source of geomagnetically effective corpuscular radiation.
4) Filaments and Corona � Their Geoactive Effects
Filaments � prominences � occur in the external solar layers above the photo-
sphere, in the chromosphere and in the inner and middle corona; in the case of rising
filaments they sometimes penetrate to the outer corona. Since it can be dssumed that
they are produced by the condensation of coronal matter along the lines of force of the
local magnetic fields, leaving the photosphere, the structure of such fields can be de-
duced from their shape. At the same time prominences give a conception of the arran-
gement of the magnetic fields in the direction perpendicular to the solar surface while
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�
filaments and the fine structure of the chromosphere indicate the magnetic fields distri-
buted parallel to the surfaces of the Sun.
On the basis of the relation of filaments to the surrounding magnetic fields we
classified filaments into three groups [6, 61], which proved to be very useful in in-
vestigating the geoactivity of filaments. It was later found that this classification can
be made in keeping with the development of filaments [6, 62] and therefore we give
here the different types in the order of the phase development of the filament.
1) Bound Filaments. These are the youngest type of filaments occurring directly in
the active regions and, as is clearly shown by their shape, they are under the influence
of the local magnetic field. They persist in the active region without any great changes
until they more or less suddenly become type 2 or gradually become type 3.
2) Unstable Filaments. Active, eruptive and disappearing filaments belong here,
in the order according to the suddenness of the changes occurring in them. They occur
again in active regions, not necessarily directly in the sunspot groups but always under
the influence of the local magnetic field, the basic time changes of which are, we as-
sume, the actual cause of instability of the filaments of this type.
3) Free Filaments. These include all filaments occurring clearly outside the active
region which are thus not under the influence of local magnetic fields. They are fila-
ments of the oldest phase of development which were produced in the active region as
type 1 and outlasted the period characterized by sunspot and flare activity in which
there occurred the strongest time changes in the magnetic field. In this period they
begin to move gradually further away from the active region in the direction of the
poles and to take up a position roughly in the direction of the solar parallels.
To the different types of filaments defined by our "magnetic" classification, one can
ascribe*) different types of prominences according to the "motion" classification [63]
Table VI
Classifications of different types of filaments-prominences
Classification
Magnetic
Motion
Morphological
1. Bound
filaments
2. Unstable
filaments
3. Free
filaments
electromagnetic
prominences
,
eruptive
prominences
chaotic
prominences
particularly prominences of type III a)�c) and less
active type I a)�c)
particularly prominences of type II a)�b) and more
active type of I a)�c)
some prominences of type V
*) If the filaments in question were observed on the solar limb as prominences.
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or the classical "morphological" classification [64], based on quite different principles
(Tab. VI).
The geoactivity of filaments � prominences � has already been investigated in a
number of papers [65-67]. A certain connection between filaments and geomagnetic
activity was statistically proved in the period before the minimum of solar activity,
and this was explained by the fact that filaments could be the source of slower corpus-
cular streams exciting smaller geomagnetic storms with a gradual commencement,
repeating after 27 days as a consequence of
Ap 0-
solar rotation. However, papers have also
20
appeared which, on the basis of statistical
methods, refute such a connection [68-71].
150-
100-
50-
Nr�
-i 6 4 a a 4--i 6 4 a 6 4-4 6 a 644 6 4 a a 44 6 4 26 4-i 6 4 a 5 4 d
261X-27D(.1957 9111958 19.1/11958 23.V111958 1111.1958 19.1X.1959
Fig. 25. Time dependences of geomagnetic activity after passages of unstable filaments through
centre of solar disc.
The question of the geoactivity of filaments, however, requires a more detailed
investigation using not only statistical methods but also methods of analyzing the
individual cases [72-77] which led to the need for the elaboration of the above
classification of filaments. It was on the basis of such a classification that we could
prove that there only seems to be disagreement in the conceptions of the geoactivity
of filaments because the different types of filaments have different results, as is seen
below:
Bound filaments: The geoactivity of these filaments was investigated by comparing
the course of the geomagnetic activity with the CMP of the filament [6, 7]. It was
� clearly shown that there is no increase in geomagnetic activity after the CMP of
filaments of this type.
Unstable filaments: When investigating the geoactivity of filaments of this type we
used different methods, chosen in keeping with the character of the problem to be
solved, and arrived at the following conclusions [7]:
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When these filaments pass through the centre of the solar disc (or its immediate
neighbourhood � max. a few degrees), a geomagnetic disturbance, usually a strong
storm, occurs in 100% of the cases (Fig. 25). An increase in geomagnetic activity occurs
even after the CMP of some non-central filaments oriented in the direction of the
meridian (Fig. 26). The value of the time interval between the CMP or between the
disappearance of a filament and the commencement of the storm varies between 27
and 53 hrs and it seems that it might depend on the degree of activity of the filament
(Tab. VII).
Ap
100-
50
0
.'"'" � .............. ��
����.
1 w
0 +1 +2 +3 +4 -1 0 +1 +2 +3 + 4 - 0' +; +31 + d
1957 1958
1959
Fig. 26. Course of ,4p-indices after CMP of non-central meridional filaments. The curves relate to
the dates as follows: 1957: 14. V.; � . �. 22. V.; . 27. VII.; � � � 8. VIII.;
16. XI.; 1958: ----1. X.; � � 9. X.; 16. X.; 2. XII.; � . � . 26. XII.; 1959:
8.� 9. II.; � 3.V.; � 10. V.; � . � . 22.V.; 2. IX.
Free filaments: The indisputable geoactivity of filaments of this type was proved
by an analysis of the different cases based on a comparison of the geomagnetic activity
after the CMP of a filament in the periods before minimum solar activity [6].
It was found that as long as there is no local magnetic field between the free filament
and the equator, then there is always an increase in geomagnetic activity after the
CMP of the filament in a time interval comparable with the values for the unstable
filaments [7]; thus the conception of the existence of corpuscular streams with very
small velocity (interval of 4 or more days) is not confirmed [66, 78].
Here we give only the results valid for isolated filaments so that their geoactivity can
be compared with that of other expressions of 'solar activity, discussed in the preceding
paragraphs separately.
29 Geofysikalni sbornik 1963
449
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3
Table VII
Mean values of time interval for different sets according to degree of activity
Maximum
degree of activity
Medium
degree of activity
Lowest
degree of activity
No.
of cases
No.
of cases
No.
of cases
time interval
in hrs.
velocity
in km/sec
28.3 � 0.6
1500
2
37.9 � 0.9
1100
11
50.9 � 0.8
800
7
The results given here lead one to think that, due to the practically 100% connection
between suitably placed unstable and free filaments and the geomagnetic activity, it is
these that are the expression of solar activity which is the direct source of geomagne-
tically effective corpuscular radiation. However, further invesligations [59] showed
that the question of determining the direct source is not so simple; the whole matter
becomes clearer if the connection with the solar corona is taken into consideration.
The Corona and its Connection with Filaments
It is usually stated that the solar corona, changing markedly during the eleven-year
cycle of solar activity, can be characterized by three basic types (Fig. 27):
a) The minimum type occurs usually in the period of the minimum of sunspots. It
Fig. 27. Tykes of solar corona (maximum, intermediate, minimum) in relation to zones of promi-
nences, marked by shorter radial lines (after [79]).
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�.'tist�t�
k
Fig 28. Comparison of structure of inner corona from 12. X. 1958 [80] with chromospheric situa-
tionaccording to solar map from Meudon. Since times of two observations do not exactly agree
comparison is valid only for more permanent events.
is characterized by a particularly simple regular shape with long equatorial wings,
without complex structures.
b) The intermediate type appearing in periods of medium solar activity is distin-
guished by a more complicated and less regular structure consisting usually of several
coronal wings.
c) The maximum type, which is formed during high solar activity, usually has a very
complicated ray-like shape with many coronal wings and streams.
The above types represent only the average idealized corona; in reality its instanta-
neous shape is given by the distribution of the different expressions of solar activity on
the edge of the disc and thus also of the local magnetic fields. The best known and
290
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most pronounced is the connection between coronal formations and prominences.
A certain coronal wing is sometimes regarded as a large three-dimensional copy of a
filament which is in the base of this wing [1].
If we take into consideration the distribution of filaments (prominences) given above,
we see their close connection with the shape of the corona. To bound prominences.
as long as they occurred in the region of simpler local magnetic fields, one can ascribe
the arched structure occurring in the base of the elongated elements � "helmets" �
from the Sun (Fig. 28). When they occur in strong more complicated fields (sunspot
groups) only arched formations are found. As regards unstable prominences, we found
[7] that they correspond to coronal streams of cylindrical shape (Fig. 29) usually
ascribed to facular fields [81].
Fig. 29. Coronal streams above facular fields in corona
from 14.1. 1926 (after [81]).
Free prominences are not seen in the corona above them by any corresponding
formation.
We can now go on to explain the conditions for the emission of geornagnetically
effective solar corpuscular radiation. The observed transformations of the bound
(non-geoactive) filaments into the unstable type (geoactive) must obviously correspond
to a change in the appropriate coronal formations above them. This, together with
the minimum type of corona at free (also geoactive) filaments, permits the assumption
that coronal formations represent the paths of corpuscular streams. The geoactivity of
unstable filaments occurring on the centre of the solar disc, which has been proved
quite definitely, is explained by a broad, favourably directed coronal stream rising
above them, which in this case is pointed towards the Earth. The geoactivity of free
filaments, which occurs if the filaments are high-latitude ones, can be explained by
the concentration of the emitted corpuscles into the equatorial plane as a result of the
effect of the total solar magnetic field, i.e. in the equatorial coronal wings which are
aimed towards the Earth. In this way it was possible to explain the origin of geomag-
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�
netic disturbances which are ascribed to hypothetical M-regions [6, 82-84]. If
a local magnetic field appears between the free filament and the equator (non-geo-
active sunspot group), the arrangement of the minimum corona is disturbed and the
corpuscular radiation is deflected from its original direction � negative effect of spots
occurs.
It remains to explain that in some cases a geomagnetic storm occurs even during the
passage of non-central unstable filaments through the central meridian [7].
a
0
0
WE
Fig. 30. Diagram of position of filament for different configuration of active regions.
It can be assumed that if the local magnetic field is temporarily compensated the
corona may prematurely become the minimum type with equatorial wing pointing to
the Earth and the emitted particles then move in the same way as in the case of free
filaments. In this way one can obviously explain why there is no increase in geomag-
netic activity after the CMP of active regions occurring symmetrically with respect to
the equator but that after the passage of a pair of active regions somewhat displaced
in heliographic longitude a magnetic disturbance sometimes occurs [85]. The explana-
tion is obvious from the representation of the magnetic fields excited during simple
configurations of idealized groups of spots [86]. It is seen from Fig. 30a that with a
symmetrical arrangement of the sunspot groups the central filament, if it is formed,
would be bound to the fields of both groups. In this case it is not very likely that there
would be a synchronous change in both magnetic fields and, moreover, a change such
as to cause the conversion of the filament into an unstable type. There is thus no reason
for an increase in geomagnetic activity at such a configuration.
If, however, the arrangement shown in Fig. 30b occurs, then the central filament, if
it occurs here, will try to take up a position along the boundary between the magnetic
fields of the two groups of spots. In this case a change in magnetic field of only one-
group with which the filament is connected is sufficient for the transition to the un
stable type; this gives rise to a favourable situation for the origin of a geomagnetic
disturbance.
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5) Deductions � On the Problem of Geomagnetic Storm Prognosis
The analysis made above mainly concerned individual solar phenomena from the
point of view of their geoactive effects. It is quite obvious, however, that for a satis-
factory explanation of the emission of corpuscular radiation, particularly in con-
nection with the prognoses of geomagnetic storms, one cannot confine oneself only to
separate investigations into the geoactivity of the above phenomena.
The conceptions on the role of the corona in the emission of corpuscular particles,
discussed above, permit filaments to be regarded as indicators of coronal formations;
this is of great importance in forecasting geomagnetic activity since the corona has not
yet been continuously observed in its whole extent.
On the Determination of the Direct Source of Corpuscular Streams
The question is, whether filaments contribute directly by their mass to the formation
of corpuscular streams, as can be expected from the high percentage of cases when
geomagnetic storms were preceded by filaments, or whether filaments merely deter-
mine the shape, position and change in the corresponding coronal formations which
were themselves the source of corpuscular streams. If we take it that filaments are the
source, then in the case of free filaments it should be possible to accept the conception
according to which hydrogen masses escape fro c filaments by diffusion into the
surrounding corona [66], where they are quite ionized and the protons and electrons
thereby released form the base of the corpuscular streams. This is also borne out by
the slow weakening of the filaments which often lasts for several rotations. In the case
of unstable filaments a larger amount of hydrogen atoms would get into the outer
corona which, after ionization, would give rise to the possibility of the origin of impor-
tant corpuscular streams.
The Geoactivity of the Active Region as a Function of its Phase
of Development
Let us first assume for the sake of simplicity that the active region is isolated. In
order to understand the character of its geoactivity the duration of the active region is
substantially divided into two periods: the first period is limited by the instants of the
formation and decay of the facular fields and the second is given by the existence of
a filament which was produced in the active region and outlasts the first period without
disappearing. This latter period lasts from the decay of the facular fields up to the
gradual decay of the filament.
As regards the geoactivity of the active region, two quite different cases may occur
in the first period according to the instantaneous situation in the active region during
CMP. If the conditions for the emission of, a geomagnetically effective corpuscular
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stream, discussed in detail in the preceding paragraphs, are not satisfied a complete
decrease in geomagnetic activity follows. In the opposite case a geomagnetic storm
with sudden commencement occurs.
The geoactivity in the second period is clear as long as the region is isolated. After
the CMP of the active region, which in this case reduces merely to a free filament, there
follows a geomagnetic disturbance or storm with gradual commencement. This
simple picture is of course complicated by the fact that not always only isolated active
regions occur on the Sun. In the period around the maximum of solar activity, in
particular, there is often a considerable concentration of different local magnetic
fields in the immediate neighbourhood of the central meridian. It is therefore more
difficult in periods of greater solar activity to determine in a simple way when a geo-
magnetic storm begins.
The negative effect of spots, causing the decay or temporary interruption of geo-
magnetic disturbances from the hypothetical M-regions, is the reason why these
regions cannot be expressed otherwise than in the period of smaller solar activity,
when there are less spots.
We proved of recurrent geomagnetic storms that they are produced by the joining
up of several disturbances [82 � 84]. A disturbance with a sudden commencement,
after the CMP of an active region through the centre of the solar disc, may be followed
by disturbances with a gradual commencement after the CMP of high-latitude fila-
ments.
Prognoses of Geomagnetic Activity
On the basis of the above results, to which special solar observations contributed to
a great degree [87, 88], it was possible to elaborate a method for the prognosis of
geomagnetic activity') and also on the basis of our own solar observations to start
issuing test forecasts.
In prognoses one must distinguish the degree of reliability of the solar bases, since
this is reflected in the varying degree of accuracy of the prognoses. The most exact are
prognoses of the first kind on the basis of changes seen directly in the central solar
meridian; this, of course, requires continuous detailed observation of the Sun for
forecasting the time dependence of the geomagnetic activity (i.e. of all geomagnetic
storms and smaller disturbances as well as geomagnetically quiet periods), which
cannot be ensured at one station on the Earth. Such a prognosis can be given for a
maximum of two days ahead. At sudden changes a 28 �38 hr interval is commonly
used, the length of which is made more exact according to the estimated degree of
suddenness of the change in the solar situation. Prognoses of this kind should agree
practically 100% with reality within the limits of accuracy of the interval used since
here one is mainly determining a certain phenomen from a total of other phenomena
on the basis of relations which in principle are known. High agreement of the
*) This will be published in detail later.
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CONCLUSION
forecasts of the first kind with reality is actually observed in
1-4 practice; of course, there are not many of them because data
from continuous observation of the Sun are not available.
1/40 Prognoses of the 2nd kind differ from the first group in that the
decisive changes were not observed directly but only the possi.
� bility of such changes was estimated from the character of the
solar situation on the central solar meridian. The accuracy of
�: 6
prognoses of this kind, which are issued for the same period
0 ahead and using the same time interval as for prognoses of the
5 17; first type, is limited mainly by the degree of probability of extra-
^ polating the development of the active region.
Less accurate are prognoses of the 3rd type, based on obser-
vations of the solar situation before the CMP, when extra-
� bJ)
���
polation of the development of the active region must be made
O s for a period of several days. These prognoses, which do not
have to be made if data from continuous observation of the
.0
Sun are available, may be of greater importance only in periods
a �
of lower solar activity, when the starting point for prognoses
cl
E are mainly long-term free filaments. In periods of greater solar
0 4)
activity they must be made as accurate as possible by prognoses
0
O I
at least of the 2nd type.
� 0
.E For illustration we give an example of a prognosis together
� --
O cz
with the course of geomagnetic activity for one 27-day period
4.4 N
(Fig. 31). It is obvious that as long as solar observations were
0
a 0 � avaimble, the prognoses could determine storms with a sudden
O -a
cS commencement as well as several smaller disturbances and even
u
� the quiet periods.
Prognoses of geomagnetic activity based on the above prin-
� ciples, as long as our own solar observations were available,
a 0
have been made since September 1959.
0 0
It is seen from the 135 prognoses issued so far that they
> agree with reality in 90% of the cases so that the above method
� can at present be regarded as very good; this is also borne out
.9.
by the correctness of the conclusions based on our analysis of
p.)
the connection between solar and geomagnetic activity.
cct
0
0
0
The problem of the origin of geomagnetic storms, as dis-
cussed here, represents a relatively very broad complex of
problems which are solved in this connection. In addition to
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a general view of the partial phase of the general development of geomagnetic
storms, our paper gives some new results of research, obtained recently, which
contribute to the classification of storms and to clarifying the relations between
geomagnetic and solar activity.
When classifying geomagnetic storms type analysis showed that the majority of
storms has a two-phase course although one cannot neglect even that number of
storms which exhibits a one-phase course. Such storms have a tendency to occur only
in a certain period of the day.
A systematic investigation of the relations between solar and geomagnetic activity
provided some important data contributing towards a decision on the causes of geo-
magnetic storms.
The relatively comprehensive material, on the basis of which the influence of sun-
spots on geomagnetic activity was determined, showed that the spots in themselves can-
not be geoactive; a certain connection, found earlier in a number of papers, can be
explained by the fact that other solar effects in the regions of spots were not taken into
consideration.
An analysis of the results of observing flares, which was made in a number of papers
both by statistical methods and for some individual cases, showed that flares might
play a role in events which are followed by an increase in geomagnetic activity (in par-
ticular the occurrence of flares might disturb the shape of local magnetic fields on
the Sun, if of course the flares themselves are not the consequence of the changes in
these fields); it was found quite definitely, however, that flares are not the direct
source of geomagnetically effective corpuscular radiation.
A study of filaments and the corona provided new results from the point of view of
the causes of geoactivity. We made a new division of filaments into three groups and
arrived at the conclusion that the filaments classified in unstable and free groups are
very closely related to sources of geoactive radiation. However, it is not a simple
problem to determine the direct source. It was found necessary to take into considera-
tion phenomena occurring in the corona. An important role here is played by the
approximately equatorial coronal streams or wings. The influence of the total magne-
tic field of the Sun is also very important in directing corpuscular radiation (parti-
cularly ejections connected with free high-latitude filaments).
The correctness of the conclusions we have derived is borne out by the reliability of
the prognoses of geomagnetic activity based on our conceptions of the geoactivity of
expressions of solar activity. The results obtained permit a unified interpretation of the
connection between geomagnetic and solar activity throughout the solar cycle.
It is natural that it has not yet been possible to explain quite satisfactorily all the
solar situations and the level of geomagnetic activity connected with them, on ac-
count of the very complicated conditions, sometimes reigning on the Sun. A number
of other problems will have to be clarified far such purposes, particularly as regards the
local magnetic fields of the Sun.
457
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The results obtained hitherto are mostly of a qualitative character, as followed from
an elaboration of the results of observations and the correlation of geomagnetic and
solar phenomena. This phase in research was indispensable for ensuring a sufficient
base of new experimental grounds; it contributed towards the discovery of a series
of new laws and should be continued. However, the problems have not yet been
solved from the quantitative point of view as regards the investigation of physical
conditions and the interpretation of the causes of the effects, as they actually occur, by
the proposal of suitable theoretical models. These questions will be the subject of
further work.
The discussion of events on the Sun shows that a decisive role in their formation is
played by the magnetic fields, their distribution and dynamics. It is therefore impor-
tant to explain their role in connection with geoactive processes and thus in relation to
the origin of geomagnetic storms. In this respect it will be expedient to use inter alia
the results of research into the internal geomagnetic field (particularly of continental
geomagnetic anomalies and isoporic expressions) at present being done in our depart-
ment [89] and at the same time to carry out model experimental investigations of the
general magnetic fields with the possibility of applying the conclusions derived to the
study of solar magnetic fields. From the theoretical point of view one must concen-
trate on the application of magnetohydrodynamical laws in explaining the causes of
magnetic fields.
It is well known that the hydromagnetic processes taking place in the Earth's inte-
rior, which to a certain extent participate in the formation and maintenance of the
Earth's magnetic field, have a relatively great similarity to processes on other cosmic
bodies, i.e. on stars and thus also on the Sun [90, 91]. It is therefore expedient to make
use of the results obtained from research into solar phenomena for the study of the
Earth's magnetic field and vice versa. This procedure, common at many laboratories
throughout the world where questions of research into the geomagnetic field are
solved, is quite logical. This is because while relatively much is known about the geo-
magnetic field and its dynamic expressions (whether external or internal) we are not
able to study directly hydrodynamic events appearing as the magnetic field on the
Earth's surface. It is therefore indispensable that, apart from an analysis of the sur-
face expressions of the geomagnetic field, analogies should be sought for the hydro-
magnetic processes in the Earth's interior and studied in those places where the mecha-
nisms of such events, i.e. particularly on the Sun, can easily be investigated.
Quite analogously, research into the external geomagnetic field, the structure of
which is observed at geomagnetic observatories, must use data from studies of pro-
cesses, which are the source of the above disturbances or at least influence them to
a certain extent, to explain the causes of geomagnetic disturbances.
Research work will have to be carried out along such lines both from the point of
view of obtaining new experimental data and as regards theoretical generalization.
Received 13. 4. 1963 Reviewer: A. Zatopek
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a
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Vj,tah
K PROBLEMATICE VZNIKU GEOMAGNETICIa'CH BOUM
Bohumila Bednarova-Novakova, Vaclav Bucha, Jaroslav Halenka,
Mojmir Konan)',
Problernatika vzniku geomagnetickjtch boufi, jak je diskutovana v pfedlokne praci,
pfedstavuje pomerne girol4 komplex iiko1�, ktere jsou v teto souvislosti fegeny.
Krome souhrnneho pohledu na dilI faze celkoveho vjfvoje geomagneticl4ch boufl
jsou uvedeny nektere novo vyisledky vYzkumu, nami dosaiene za posledni obdobi,
ktere pfispivaji ke klasifikaci boufi a k objasneni vzajemnSich vztahii mezi geomagne-
tickou a sluneeni aktivitou.
Pfi klasifikaci geomagnetickjrch boufi typova analysa ukazala, e vagina boufl ma
dvoufazoq pritheh, i kdyt nelze zanedbat ani east, kter�kazuje pritheh jedno-
fazovyr. U techto boufi je patrn�endence vyiskytu pouze v ureitem dennim obdobi.
Pi systematickem vygetfovani vztahti mezi sluneeni a geomagnetickou aktivitou
byly ziskany nektere &Waite poznatky pfispivajici k rozhodnuti o pfieinach vzniku
geomagnetickjich bouff.
Pomerne rozsahlSi material, na jehoi zaklade bylo provedeno posouzeni vlivu slu-
neenich skvrn na geomagnetickou aktivitu, ukazal, e skvrny samy o sobe nemohou
11)4 geoaktivni; ureitou, nekteqmi pracemi dfive zjigtenou souvislost lze vysvetlit tim,
le nebylo plihlIeno k vyiskytu dalgich sluneenich jevei v oblastech skvrn.
Rozbor vYisledkft pozorovani erupci, kterl jsme ptovedli v fade praci jak statistic-
14mi metodami, tak pro nektere jednotlive pfipady, ukazal, e erupce by se mohly
podilet na dejich, po nich tale nastat zvYfgeni geomagneticke aktivity (zvlagte tim,
vjiskyt erupci by mohl narugovat a menit tvar mistnich magneticl4ch poll na Slunci,
pokud ovgem samy erupce nejsou diisledkem zmen techto bylo vgak nami zjig-
ten�, e erupce nejsou pfin4m zdrojem geomagneticky teinneho korpuskularniho
zafeni.
Studium filament-a a korony pfineslo nektere nove vSisledky z hlediska pfiein geo-
aktivity. Provedli jsme nove rozdeleni filamentil do ti skupin a dogli k zaveru,
filamenty zafazene do skupin nestabilnich a voliVich maji velice blizk vztah ke zdro-
jiim geoaktivniho zafeni. Ure'eni pfimeho zdroje vgak neni jednoduchYr problem;
ukazala se nutnost pfihlednout k jev�m, ktera nastavaji v korone. DfileIitou roli zde
hraji pfibliine ekvatorealni koronalni proudy nebo kfidla. Ve1l4 vjiznam pfi nasmero-
vani korpuskularniho zafeni ma t�liv celkoveho magnetickeho pole sluneeniho
(zvlagte pH vytronech souvisicich s volqmi filamenty vysokogifkoqmi).
Pro spravnost zavera, jet' jsme odvodili, mluvi .spolehlivost prognos geomagneticke
aktivity, zaloienYrch na nagich pfedstavach o geoaktivite projeva sluneeni einnosti.
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5,1
Ziskane vysledky umolfluji jednotny vyklad souvislosti geomagneticke aktivity se slu-
neeni einnosti v celem obdobi sluneeniho cyklu.
Je pfirozene, e zatim nebylo mono vysvetlit zcela uspokojive vgechny sluneeni
situace a $ nimi souvisici stay geomagneticke aktivity vzhledem k velice sloiitym pod-
minkam, ktere nekdy na Slunci panuji. Pro tyto ueely bude tfeba vyjasnenl jet e dal-
gich otazek zvlagte pokud jde o lokalni magneticka pole sluneeni.
Dosud ziskane vYsledky jsou vetginou kvalitativniho charakteru, jak vyplynuly ze
zpracovani vYsledkit pozorovani a Z korelace geomagnetickych a solarnich jeva. Tato
faze nagi vYzkurnne einnosti byla nezbytne nutna pro zajigteni dostaeujici baze novych
zakladnich materialli z pozorovani, pfispela k objeveni fady novych zakonitosti a je
nutno v ni pokraeovat. Uvedend problematika vgak dosud nebyla fegena po strance
kvantitativni, pokud jde o vygetfovani fysikalnich podminek a objasnovani priein
zkoumanYch jevit, jak ye skuteenosti probihaji, navrIenim vhodnych teoretickYch
modelit; tyto otazky budou pfedmetem dali nag einnosti.
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59
�
Pe3iome
K IIPORTIEMATVIKE BO3H14KHOBEH1451 rEOMATI-114THbIX BYPI3
Bohumila Bednafova-Novakova, Vaclav Bucha, Jaroslav Halenka,
Mojmir Konenjr
lipo6nemaTHxa BO3H11K140BeHHA reomarHHTHbix 6ypb B TOM wane, Rai( oHa pac-
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110TO 113.nytie114n.
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3peHH5i 11p14=u4H BO3HHKHOBeHHA Te0aKTHBHOCTH. BMA� nposegeHo HOBO e nonpa3ne-
neime BOJIOKOH Ha Tpx rpynnbi 14 cgenall BbIBOXI, BOAOKIla, oTHecembie K CB060,II-
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reoaxTHBHoro H3nriemoi. OnHalco onpeneneHHe HenocpencTBeHHoro Haromunca He
30 Geofysikalni sbornik 1963
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