Sunspot cycle

“ This longer cycle, underlying the sunspot period, alters the time of occurrence of the sunspot maxima in relation to the preceding sunspot minima. He makes out three periods in solar activity, of between three and four years, about eleven, and about thirty-five year respectively. These are related as 1:3:9.
It is clear that the existence of a thirty-five-year period will account for many of the views that have been advanced in favor of a progressive change of climate. A succession of a few years wetter or drier than the normal is likely to lead to the conclusion that the change is permanent. ”

“ Sunspots can occur unexpectedly, and the life span of individual sunspots is variable. The ELEVEN-YEAR SUN SPOT CYCLE is a regular cycle of sunspot activity that has a minimum and maximum level of activity that occurs every 11 years. During periods of maximum activity, the ionization density of all the layers increases. Because of this, the absorption in the D layer increases and the critical frequencies for the E, F1, and F2 layers are higher. ”

“ Before these have all died away, a few small spots, the heralds of a new cycle of activity, begin to appear in high latitudes.
This law, called after SPÖRER, its discoverer, indicates that the origin and source of sunspot activity lie within the Sun. At one time it was thought that sunspots were due to some action of Jupiter—for Jupiter moves round the Sun in 11.8 years, a period not very different from the sunspot cycle—or to some meteoric stream. ”

“ It would be possible to apply correlation formulas to the Arizona tree records and perhaps to the sequoias and construct a probable rainfall record for long periods of time, but apart from Huntington's study of the "Climatic Factor in History," the chief use of such a record would be in studying the laws which govern rainfall; and this is best done through cycles. We shall find that the sunspot cycle plays an important rôle in rainfall. ”

“ While all adolescent suns do not pass through a pulsating stage, at least not visibly, when looking out into space you may observe many of these younger stars whose gigantic respiratory heaves require from two to seven days to complete a cycle. Your own sun still carries a diminishing legacy of the mighty upswellings of its younger days, but the period has lengthened from the former three and one-half day pulsations to the present eleven and one-half year sunspot cycles. ”

“ In order to test for possible variations in the sunspot curve during these 500 years, the tree record from 1420 to 1909 has been divided into 8 periods of approximately 60 years each and the form of the 11-year period obtained in each. This is shown in figure 33. From this it appears that the 11-year cycle is not uniform throughout the whole 490 years covered by the curve. In general the cycle shows 2 maxima and 2 minima. From 1420 to 1660 the second minimum is generally the deeper. For the next 60 years the curve flattens out in a striking manner. ”

“ Other solar cycles. — Plate 12, g to p, shows the multiples of the solar cycle. Pattern G gives the Arizona tree record analyzed at 23.5 years. It shows a slightly irregular vertical row of crests. This is best seen by tipping the pattern so that the eye views it from a low angle instead of perpendicularly as in ordinary reading. A line slanting down to the left giving a period at nearly 22.2 years would answer quite as well. The lower third is somewhat broken by the triple sunspot period showing in it. ”

“ The 11-year period is plainly evident through most of the record and for some centuries is the predominant cycle, but for long periods other slightly differing cycles, such as 10 years, 12.6 years, or 13 years, are more evident. It is as yet impossible to say whether at these times there was a real change in the sunspot period, whether some subordinate period is operating in the sun, or whether only local conditions of some kind are the controlling factor.
The yellow pines of northern Arizona are dry-climate trees. They have a modified winter precipitation of the temperate zone. ”

“ Plate 12, q, is made from the standard 5-year period with a setting at 5.0 years. The first pattern in plate 12 shows the regularity of the sunspot period since 1610 A. D. The interval in the latter part of the eighteenth century, when the cycle was reduced to less than 10 years, is distinguished by a bending of the row toward the left. This is followed by a deflection toward the right during the interval of readjustment from 1790 to 1830. The direction of any row becomes an exact measure of its period.
If a period is constant, the row of crests is straight. ”

“ Brückner's Thirty-five-year Cycle.—Of more importance than the results thus far reached for the sunspot period are those which clearly establish a somewhat longer period of slight fluctuations or oscillations of {hws|cli|climate}} climate, known as the Brückner cycle, after Professor Brückner, of Berne, who has made a careful investigation of the whole subject of climatic changes and finds evidence of a thirty-five-year periodicity in temperature and rainfall. ”

“ But let us see what the cycle association between solar spots and terrestrial weather actually is, or rather of what nature it promises to be, for as yet the true nature of the association has not been made out.
It has been found that in a period of about eleven years the sun’s surface is affected by what may be described as a wave of sun-spots. There is a short time—a year or so—during which scarce any spots are seen; they become more and more numerous during the next four or five years, until they attain a maximum of frequency and size ”

“ On the first examination of these sections in November 1912, it was evident that their growth follows with fidelity the sunspot curve since 1830. This may be traced in the curves below and in the accompanying photographs of two of the sections in plate 8. It will be seen at once that there is a rhythmic sway in the growth, groups of large rings alternating with small ones. The arrows placed in the photographs mark the years of maximum sunspots. Taking the group as a whole, the maximum growth comes within 0.6 year of the sunspot maximum. ”

“ It is like a checker-board of trees in an orchard; they line up in many directions with attractive intensity. But plate 9, c, helps remove some of the complexity of the sunspot problem. It shows us that while these various periods are apparent, they are improbable and needless complications. The diagram supplies a basis for profitable judgment in the matter. Hence to avoid just such awkward cases as the sunspot curve, a differential pattern is considered to be a necessary accompaniment of the periodogram in doubtful cases. ”

“ Greater solar radiation increases the evaporation over the oceans, so that the air becomes more humid. This moist air is carried by atmospheric currents over the land, where the moisture is condensed into clouds and greatly increases the rainfall. At the same time the cloud canopy shuts off some of the direct heat of the sun, and we have the curious paradox that at times of sunspot maximum, or greatest solar radiation, the temperature of the earth’s surface is lowest. ”

“ Similarly, near the sun’s poles we should find a gradual darkening, as is the case; but from five degrees to thirty degrees latitude, the sun, in its rotation, by reason of the inclination of its axis, passes at every point directly beneath the planets, or within their area of control, and here we find the solar spots in their greatest number, size, and intensity. These sun-spots cross the face of the sun in about fifteen days, and vary in development from year to year, having a cycle of 11.11 years from maximum to maximum. They also have a long cycle of about fifty-six years. ”

“ The question naturally arises, "If the Sun, to which the Earth is indebted for nearly everything, passes through a change in its activity every eleven years or so, how is the Earth affected by it?" It would seem at first sight that the effect should be great and manifest. A sunspot, like that of February 1905, one thousand times as large as Europe, into which worlds as large as our Earth might be poured, like peas into a saucer, must mean, one might think, an immense falling off of the solar heat. ”

“ The trees near sea-level, both at Christiania and on the outer coast of Norway, return again to the 11-year period. The former do not cross-identify well and the latter show occasional variations, such as double-crested period, inversion, etc. Variations of this kind were noted in different radii of the same tree. The trees from the south of England show slight relation to the solar cycle. They show more prominently other variations, which, taken between 1870 and 1900, may have given rise to Lockyer's 3.8-year period (1905, 1906) . ”

“ A 7-year period is also frequently observed, and the combination of the 7-year and 11-year periods may be the cause of these trees showing the double sunspot period prominently through most of their record by interfering to suppress alternate 11-year maxima. A triple sunspot period is very evident in the last 200 years, but is practically lost in the preceding 300. The pines and sequoias agree in showing a long period of about 100 years. The record of the pines is not long enough to give it much precision, and 120 years fits it more nearly. ”

“ Figure 28 gives details of the time relation between tree-growth, rainfall, and solar activity. In figure 29 the curves of figure 28 have been summated on an 11.4-year period, as was done in figure 25. At the bottom is the sunspot curve from 1834 to 1912 inclusive; directly above it is the curve of rainfall for the vicinity of Windsor, compiled chiefly from records at Hanover and Concord and covering 1835 to 1912; above that is the tree-growth from 1834 to 1912, and in the upper line the sunspot curve is repeated with a displacement of — 3 years. ”

“ Utterly inconsistent with all that is yet known of the sun’s physical action, as it may seem, on à priori grounds, to suppose that spots, currents, or other local disturbances of the sun’s surface could produce any but general effects on the earth as a whole, yet if we shall find that particular effects are produced in special regions of the earth’s surface in cycles unmistakably synchronizing with the solar-spot-cycle, we must accept the fact, whether we can explain it or not. ”

“ In countries where the most important interests are manufacturing and ocean transportation, the 'weather' is the first consideration; in lands where the agricultural interests are predominant, although the weather is important, it is more essential to have an idea of the climatic or seasonal changes. Thus if the sunspot period could be shown to have a large influence on the climate of any region, we should be able to forecast to a corresponding extent the general characteristics of future seasons, and lay plans accordingly. ”

“ We are certainly not going so far as to say that any connection has been definitely established between a season of exuberant sun-spots and a season remarkable for excessive warmth, but, as we know that there is a connection between the magnetic condition of the earth and the state of solar activity, it is by no means impossible that climate and sun-spots may also stand in some relationship to each other. ”

“ But when, on the contrary, a series of changes in the physical geography of the globe, or any other supposed cause, occasions an elevation of the general temperature,—when there is a passage from the winter to one of the vernal or summer seasons of the great cycle of climate,—then the order of the migratory movement is inverted. The different species of animals and plants direct their course from the equator towards the poles; 698 and the northern and southern hemispheres may become peopled to a certain limited extent by identical species. ”

“ Fundamental periodic changes in the body of the sun have been suggested and, in the absence of better explanations, some such statement hazily indicating the direction in which explanation is to be sought, is perhaps the best that we can do. Planetary influence, however, has often been proposed as the cause. The near agreement between the revolution period of Jupiter and the sunspot period has naturally attracted attention. ”

“ Cloudy, or humid days, diminish the effect upon the soil of solar radiation; similar nights retard the radiation from the earth. A dry atmosphere is the most favourable for the direct transmission of the sun’s rays; and the withdrawal of the sun from any region over which the air is dry, must be followed by very rapid cooling of the soil. “The removal, for a single summer night, of the aqueous vapour from the atmosphere which covers England, would be attended by the destruction of every plant which a freezing temperature could kill. ”

“ The average period between the minima or dates of fewest sunspots is rather less irregular, since it has never been known to differ by much more than two years from the mean period of 11 years. There is some evidence that these stronger and weaker maxima themselves run in a cycle, but the period is very doubtful. Wolf, who devoted most of his life to the investigation of sunspots, deduced a period of 55 years for this longer cycle, while there are later determinations of 60, 351/2 and 61 years. ”

“ Let us apply this principle to the solar system, and endeavour to find out whether in that system we have, in relation to the heat thereof, either a cycle of operations or a reversible cycle. We have again to consider the sun as the source of all light and heat in the solar [118] system, radiating forth on every side, year by year, the countless units of heat which go to form the continuance of all planetary life and existence. One of the problems that has confronted scientific men for many years is this, Where does the sun get its supply of heat from? ”