SOLAR ENERGY VARIATIONS AND ANOMALOUS WEATHER CHANGES 
variability that exists is related to the sunspot number, 
at least in a general way. The record of sunspot number 
in the past 200 years, therefore, gives some idea of the 
character of solar fluctuations. A study of the record 
shows great irregularity. Although the average time 
from maximum to maximum has been eleven years, the 
interval between maxima has been exactly eleven years 
only three times in eighteen cycles and has varied from 
seven to seventeen years. The annual mean sunspot 
number at maximum has varied from 46 (1816) to 152 
(1947). The maxima appear to have run in cycles of 
four large values and three small values. This longer- 
period variation can also be expressed in terms of an 
80-year cycle, that is, in successive forty-year periods 
the average number of sunspots has been alternately 
large and small. 
There is some evidence that during the historical 
past solar activity has varied considerably more than 
during the past 200 years. Fragmentary observations 
and records indicate that during parts of the 13th and 
14th centuries (a period of considerable climatic stress 
in Hurope and Asia) solar activity as evidenced by very 
large and numerous sunspots was probably greater 
than it has been since, although observations were so 
few and primitive that no real comparison can be made. 
On the other hand, between 1672 and 1704 (the 17th and 
18th centuries were notably lacking in climatic stress) 
not a single sunspot was observed on the solar northern 
hemisphere, so that in 1705 when the observation of 
such a spot was announced it was considered a sur- 
prising fact of extreme scientific interest. 
THE PERIODIC CHARACTER AND GEOGRAPHI- 
CAL PATTERN OF THE ANOMALOUS 
WEATHER FLUCTUATIONS 
The flow pattern of the general circulation of the 
earth’s atmosphere, by which the world weather pat- 
tern is determined, is in a perpetual state of anomalous 
fluctuation comparable in amplitude to and much more 
rapid than the normal slow seasonal fluctuation. The 
periodic character of these anomalous fluctuations of 
the general circulation has been the subject of extensive 
statistical analysis. Components of periods ranging from 
a few days to millenia or geological epochs in length 
can be detected, but it has not been possible to demon- 
strate any regular periodicity of real statistical signi- 
ficance in these fluctuations. To all practical purposes, 
there are no established periods of anomalous fluctua- 
tion of the general circulation. 
The fluctuations occur in an almost continuous spec- 
trum of periods from the very short to the very long. 
For purposes of discussion it is convenient to group 
the anomalous fluctuations of the general circulation 
(z.e., of the world weather pattern) by length of period 
of the fluctuation concerned, in five general classes. 
A discussion of each of these classes follows. 
Geological Fluctuations. These refer to the major 
glacial and interglacial periods during geological time. 
According to the best geological evidence [7], major 
glacial epochs, at least during the last billion years, 
381 
have occurred approximately at quarter-billion-year 
intervals, but no over-all climatic trend towards more 
mild or more severe conditions is indicated. Each of 
these glacial epochs (with the exception of the Pleisto- 
cene, which is not yet terminated) continued for many, 
perhaps as much as 50 million years, being separated 
by approximately 200 million years of relatively mild 
interglacial climate. The geological evidence indicates 
that each major glacial epoch was by no means con- 
tinuous, but consisted of an extended sequence of per- 
iods of maximum glaciation (ice-sheet development) 
separated by periods of ice-free interglacial conditions. 
These glacial-interglacial sequences apparently run in 
cycles of from one hundred thousand to five hundred 
thousand years duration. 
The present Pleistocene Epoch, which apparently 
has not lasted more than one or two million years, has 
experienced four such glacial maxima, separated by 
three interglacial periods, of which the middle and 
longest one lasted for at least two hundred thousand 
years [7]. Since the Pleistocene sequence of glacial and 
interglacial climates is known in much greater com- 
pleteness and detail than that of the earlier glacial 
epochs, and since it occurred under essentially the 
present condition of topography (land and water dis- 
tribution) which determines our climatic patterns to- 
day, only this epoch is referred to in the following dis- 
cussion of glacial and interglacial climates. It is assumed 
that any deviation of the earlier glacial-interglacial 
patterns from those of the Pleistocene period are to be 
explained by the extensively different terrestrial to- 
pography of the earlier periods. 
The climatic conditions of a period of maximum 
glaciation may be characterized essentially as follows: 
1. Ice sheets covering up to 30 per cent of the con- 
tinental area of the Northern Hemisphere, with prin- 
cipal ice sheet centers between latitudes 60° and 65° 
over northeastern America and over Scandinavia, ex- 
tending southward over favorably located continental 
areas to the 40th parallel of latitude. 
2. Greatly expanded anticyclonic polar-cap circu- 
lations, with a corresponding equatorward displace- 
ment of the climatic belts and zonal wind systems, 
notably of the prevailing storm tracks of middle lati- 
tudes. 
3. Increased poleward temperature gradient in middle 
latitudes, with a correspondingly marked intensifica- 
tion of the general circulation, notably of storminess 
in middle latitudes and of the effective operation of the 
evaporation-precipitation cycle. 
4. Predominance of excessively cool and wet condi- 
tions in the middle and lower middle latitudes of max- 
imum storminess; of excessive rainfall in the inter- 
tropical convergence zones, and probably of hot dry 
conditions in a narrow intense subtropical high pressure 
belt on either side of the equator. 
In contrast the climatic conditions of a typical inter- 
glacial period may be characterized essentially as 
follows: 
1. Complete disappearance of permanent ice from 
the face of the globe on land and sea, with only tempo- 
