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The Solar Cyclonic Hypothesis

The progress of science is made up of a vast succession of hypotheses.

The majority die in early infancy. A few live and are for a time widely

accepted. Then some new hypothesis either destroys them completely or

shows that, while they contain elements of truth, they are not the whole

truth. In the previous chapter we have discussed a group of hypotheses

of this kind, and have tried to point out fairly their degree of truth
r /> so far as it can yet be determined. In this chapter we shall outline

still another hypothesis, the relation of which to present climatic

conditions has been fully developed in Earth and Sun; while its

relation to the past will be explained in the present volume. This

hypothesis is not supposed to supersede the others, for so far as they

are true they cannot be superseded. It merely seems to explain some of

the many conditions which the other hypotheses apparently fail to

explain. To suppose that it will suffer a fate more glorious than its

predecessors would be presumptuous. The best that can be hoped is that

after it has been pruned, enriched, and modified, it may take its place

among the steps which finally lead to the goal of truth.

In this chapter the new hypothesis will be sketched in broad outline in

order that in the rest of this book the reader may appreciate the

bearing of all that is said. Details of proof and methods of work will

be omitted, since they are given in Earth and Sun. For the sake of

brevity and clearness the main conclusions will be stated without the

qualifications and exceptions which are fully explained in that volume.

Here it will be necessary to pass quickly over points which depart

radically from accepted ideas, and which therefore must arouse serious

question in the minds of thoughtful readers. That, however, is a

necessary consequence of the attempt which this book makes to put the

problem of climate in such form that the argument can be followed by

thoughtful students in any branch of knowledge and not merely by

specialists. Therefore, the specialist can merely be asked to withhold

judgment until he has read all the evidence as given in Earth and Sun,

and then to condemn only those parts that are wrong and not the whole


Without further explanation let us turn to our main problem. In the

realm of climatology the most important discovery of the last generation

is that variations in the weather depend on variations in the activity

of the sun's atmosphere. The work of the great astronomer, Newcomb, and

that of the great climatologist, Koeppen, have shown beyond question that

the temperature of the earth's surface varies in harmony with variations

in the number and area of sunspots.[15] The work of Abbot has shown that

the amount of heat radiated from the sun also varies, and that in

general the variations correspond with those of the sunspots, although

there are exceptions, especially when the spots are fewest. Here,

however, there at once arises a puzzling paradox. The earth certainly

owes its warmth to the sun. Yet when the sun emits the most energy, that

is, when sunspots are most numerous, the earth's surface is coolest.

Doubtless the earth receives more heat than usual at such times, and the

upper air may be warmer than usual. Here we refer only to the air at the

earth's surface.

Another large group of investigators have shown that atmospheric

pressure also varies in harmony with the number of sunspots. Some parts

of the earth's surface have one kind of variation at times of many

sunspots and other parts the reverse. These differences are systematic

and depend largely on whether the region in question happens to have

high atmospheric pressure or low. The net result is that when sunspots

are numerous the earth's storminess increases, and the atmosphere is

thrown into commotion. This interferes with the stable planetary winds,

such as the trades of low latitudes and the prevailing westerlies of

higher latitudes. Instead of these regular winds and the fair weather

which they bring, there is a tendency toward frequent tropical

hurricanes in the lower latitudes and toward more frequent and severe

storms of the ordinary type in the latitudes where the world's most

progressive nations now live. With the change in storminess there

naturally goes a change in rainfall. Not all parts of the world,

however, have increased storminess and more abundant rainfall when

sunspots are numerous. Some parts change in the opposite way. Thus when

the sun's atmosphere is particularly disturbed, the contrasts between

different parts of the earth's surface are increased. For example, the

northern United States and southern Canada become more stormy and rainy,

as appears in Fig. 2, and the same is true of the Southwest and along

the south Atlantic coast. In a crescent-shaped central area, however,

extending from Wyoming through Missouri to Nova Scotia, the number of

storms and the amount of rainfall decrease.

(After Kullmer.)

Based on nine years' nearest sunspot minima and nine years' nearest

sunspot maxima in the three sunspot cycles from 1888 to 1918. Heavy

shading indicates excess of storminess when sunspots are numerous.

Figures indicate average yearly number of storms by which years of

maximum sunspots exceed those of minimum sunspots.]

The two controlling factors of any climate are the temperature and the

atmospheric pressure, for they determine the winds, the storms, and thus

the rainfall. A study of the temperature seems to show that the peculiar

paradox of a hot sun and a cool earth is due largely to the increased

storminess during times of many sunspots. The earth's surface is heated

by the rays of the sun, but most of the rays do not in themselves heat

the air as they pass through it. The air gets its heat largely from the

heat absorbed by the water vapor which is intimately mingled with its

lower portions, or from the long heat waves sent out by the earth after

it has been warmed by the sun. The faster the air moves along the

earth's surface the less it becomes heated, and the more heat it takes

away. This sounds like a contradiction, but not to anyone who has tried

to heat a stove in the open air. If the air is still, the stove rapidly

becomes warm and so does the air around it. If the wind is blowing, the

cool air delays the heating of the stove and prevents the surface from

ever becoming as hot as it would otherwise. That seems to be what

happens on a large scale when sunspots are numerous. The sun actually

sends to the earth more energy than usual, but the air moves with such

unusual rapidity that it actually cools the earth's surface a trifle by

carrying the extra heat to high levels where it is lost into space.

There has been much discussion as to why storms are numerous when the

sun's atmosphere is disturbed. Many investigators have supposed it was

due entirely and directly to the heating of the earth's surface by the

sun. This, however, needs modification for several reasons. In the first

place, recent investigations show that in a great many cases changes in

barometric pressure precede changes in temperature and apparently cause

them by altering the winds and producing storms. This is the opposite of

what would happen if the effect of solar heat upon the earth's surface

were the only agency. In the second place, if storms were due

exclusively to variations in the ordinary solar radiation which comes to

the earth as light and is converted into heat, the solar effect ought to

be most pronounced when the center of the sun's visible disk is most

disturbed. As a matter of fact the storminess is notably greatest when

the edges of the solar disk are most disturbed. These facts and others

lead to the conclusion that some agency other than heat must also play

some part in producing storminess.

The search for this auxiliary agency raises many difficult questions

which cannot yet be answered. On the whole the weight of evidence

suggests that electrical phenomena of some kind are involved, although

variations in the amount of ultra-violet light may also be important.

Many investigators have shown that the sun emits electrons. Hale has

proved that the sun, like the earth, is magnetized. Sunspots also have

magnetic fields the strength of which is often fifty times as great as

that of the sun as a whole. If electrons are sent to the earth, they

must move in curved paths, for they are deflected by the sun's magnetic

field and again by the earth's magnetic field. The solar deflection may

cause their effects to be greatest when the spots are near the sun's

margin; the terrestrial deflection may cause concentration in bands

roughly concentric with the magnetic poles of the earth. These

conditions correspond with the known facts.

Farther than this we cannot yet go. The calculations of Humphreys seem

to indicate that the direct electrical effect of the sun's electrons

upon atmospheric pressure is too small to be of appreciable significance

in intensifying storms. On the other hand the peculiar way in which

activity upon the margins of the sun appears to be correlated not only

with atmospheric electricity, but with barometric pressure, seems to be

equally strong evidence in the other direction. Possibly the sun's

electrons and its electrical waves produce indirect effects by being

converted into heat, or by causing the formation of ozone and the

condensation of water vapor in the upper air. Any one of these processes

would raise the temperature of the upper air, for the ozone and the

water vapor would be formed there and would tend to act as a blanket to

hold in the earth's heat. But any such change in the temperature of the

upper air would influence the lower air through changes in barometric

pressure. These considerations are given here because the thoughtful

reader is likely to inquire how solar activity can influence storminess.

Moreover, at the end of this book we shall take up certain speculative

questions in which an electrical hypothesis will be employed. For the

main portions of this book it makes no difference how the sun's

variations influence the earth's atmosphere. The only essential point is

that when the solar atmosphere is active the storminess of the earth

increases, and that is a matter of direct observation.

Let us now inquire into the relation between the small cyclonic

vacillations of the weather and the types of climatic changes known as

historic pulsations and glacial fluctuations. One of the most

interesting results of recent investigations is the evidence that

sunspot cycles on a small scale present almost the same phenomena as do

historic pulsations and glacial fluctuations. For instance, when

sunspots are numerous, storminess increases markedly in a belt near the

northern border of the area of greatest storminess, that is, in southern

Canada and thence across the Atlantic to the North Sea and Scandinavia.

(See Figs. 2 and 3.) Corresponding with this is the fact that the

evidence as to climatic pulsations in historic times indicates that

regions along this path, for instance Greenland, the North Sea region,

and southern Scandinavia, were visited by especially frequent and severe

storms at the climax of each pulsation. Moreover, the greatest

accumulations of ice in the glacial period were on the poleward border

of the general regions where now the storms appear to increase most at

times of solar activity.

decreasing sunspots.

Heavy shading, more rain with increasing spots. Light shading, more rain

with decreasing spots. No data for unshaded areas.

Figures indicate percentages of the average rainfall by which the

rainfall during periods of increasing spots exceeds or falls short of

rainfall during periods of decreasing spots. The excess or deficiency is

stated in percentages of the average. Rainfall data from Walker:

Sunspots and Rainfall.]

decreasing sunspots.

Heavy shading, more rain with increasing spots. Light shading, more rain

with decreasing spots. No data for unshaded areas. Figures indicate

percentages of the average rainfall by which the rainfall during periods

of increasing spots exceeds or falls short of rainfall during periods of

decreasing spots. The excess or deficiency is stated in percentages of

the average. Rainfall data from Walker: Sunspots and Rainfall.]

Even more clear is the evidence from other regions where storms increase

at times of many sunspots. One such region includes the southwestern

United States, while another is the Mediterranean region and the

semi-arid or desert parts of Asia farther east. In these regions

innumerable ruins and other lines of evidence show that at the climax of

each climatic pulsation there was more storminess and rainfall than at

present, just as there now is when the sun is most active. In still

earlier times, while ice was accumulating farther north, the basins of

these semi-arid regions were filled with lakes whose strands still

remain to tell the tale of much-increased rainfall and presumable

storminess. If we go back still further in geological times to the

Permian glaciation, the areas where ice accumulated most abundantly

appear to be the regions where tropical hurricanes produce the greatest

rainfall and the greatest lowering of temperature at times of many

sunspots. From these and many other lines of evidence it seems probable

that historic pulsations and glacial fluctuations are nothing more than

sunspot cycles on a large scale. It is one of the fundamental rules of

science to reason from the known to the unknown, from the near to the

far, from the present to the past. Hence it seems advisable to

investigate whether any of the climatic phenomena of the past may have

arisen from an intensification of the solar conditions which now appear

to give rise to similar phenomena on a small scale.

The rest of this chapter will be devoted to a resume of certain

tentative conclusions which have no bearing on the main part of this

book, but which apply to the closing chapters. There we shall inquire

into the periodicity of the climatic phenomena of geological times, and

shall ask whether there is any reason to suppose that the sun's activity

has exhibited similar periodicity. This leads to an investigation of the

possible causes of disturbances in the sun's atmosphere. It is generally

assumed that sunspots, solar prominences, the bright clouds known as

faculae, and other phenomena denoting a perturbed state of the solar

atmosphere, are due to some cause within the sun. Yet the limitation of

these phenomena, especially the sunspots, to restricted latitudes, as

has been shown in Earth and Sun, does not seem to be in harmony with

an internal solar origin, even though a banded arrangement may be normal

for a rotating globe. The fairly regular periodicity of the sunspots

seems equally out of harmony with an internal origin. Again, the solar

atmosphere has two kinds of circulation, one the so-called "rice

grains," and the other the spots and their attendant phenomena. Now the

rice grains present the appearance that would be expected in an

atmospheric circulation arising from the loss of heat by the outer part

of a gaseous body like the sun. For these reasons and others numerous

good thinkers from Wolf to Schuster have held that sunspots owe their

periodicity to causes outside the sun. The only possible cause seems to

be the planets, acting either through gravitation, through forces of an

electrical origin, or through some other agency. Various new

investigations which are described in Earth and Sun support this

conclusion. The chief difficulty in accepting it hitherto has been that

although Jupiter, because of its size, would be expected to dominate the

sunspot cycle, its period of 11.86 years has not been detected. The

sunspot cycle has appeared to average 11.2 years in length, and has been

called the 11-year cycle. Nevertheless, a new analysis of the sunspot

data shows that when attention is concentrated upon the major maxima,

which are least subject to retardation or acceleration by other causes,

a periodicity closely approaching that of Jupiter is evident. Moreover,

when the effects of Jupiter, Saturn, and the other planets are combined,

they produce a highly variable curve which has an extraordinary

resemblance to the sunspot curve. The method by which the planets

influence the sun's atmosphere is still open to question. It may be

through tides, through the direct effect of gravitation, through

electro-magnetic forces, or in some other way. Whichever it may be, the

result may perhaps be slight differences of atmospheric pressure upon

the sun. Such differences may set in motion slight whirling movements

analogous to terrestrial storms, and these presumably gather momentum

from the sun's own energy. Since the planetary influences vary in

strength because of the continuous change in the relative distances and

positions of the planets, the sun's atmosphere appears to be swayed by

cyclonic disturbances of varying degrees of severity. The cyclonic

disturbances known as sunspots have been proved by Hale to become more

highly electrified as they increase in intensity. At the same time hot

gases presumably well up from the lower parts of the solar atmosphere

and thereby cause the sun to emit more heat. Thus by one means or

another, the earth's atmosphere appears to be set in commotion and

cycles of climate are inaugurated.

If the preceding reasoning is correct, any disturbance of the solar

atmosphere must have an effect upon the earth's climate. If the

disturbance were great enough and of the right nature it might produce a

glacial epoch. The planets are by no means the only bodies which act

upon the sun, for that body sustains a constantly changing relation to

millions of other celestial bodies of all sizes up to vast universes,

and at all sorts of distances. If the sun and another star should

approach near enough to one another, it is certain that the solar

atmosphere would be disturbed much more than at present.

Here we must leave the cyclonic hypothesis of climate and must refer the

reader once more to Earth and Sun for fuller details. In the rest of

this book we shall discuss the nature of the climatic changes of past

times and shall inquire into their relation to the various climatic

hypotheses mentioned in the last two chapters. Then we shall inquire

into the possibility that the solar system has ever been near enough to

any of the stars to cause appreciable disturbances of the solar

atmosphere. We shall complete our study by investigating the vexed

question of why movements of the earth's crust, such as the uplifting of

continents and mountain chains, have generally occurred at the same time

as great climatic fluctuations. This would not be so surprising were it

not that the climatic phenomena appear to have consisted of highly

complex cycles while the uplift has been a relatively steady movement in

one direction. We shall find some evidence that the solar disturbances

which seem to cause climatic changes also have a relation to movements

of the crust.


[Footnote 15: The so-called sunspot numbers to which reference is made

again and again in this book are based on a system devised by Wolf and

revised by A. Wolfer. The number and size of the spots are both taken

into account. The numbers from 1749 to 1900 may be found in the Monthly

Weather Review for April, 1902, and from 1901 to 1918 in the same

journal for 1920.]