SOLAR ENERGY VARIATIONS AS A POSSIBLE CAUSE OF 
ANOMALOUS WEATHER CHANGES 
By RICHARD A. CRAIG 
Harvard College Observatory 
and H. C. WILLETT 
Massachusetts Institute of Technology 
INTRODUCTION 
This article is concerned only with the possible rela- 
tionships existing between anomalous changes of 
weather and the variations, in one form or another, of 
the output of solar energy. There can be no question 
that the sequence of weather change which is repre- 
sented by the normal diurnal and seasonal sequences of 
weather over the globe is to be explained entirely by the 
corresponding diurnal and seasonal variation of the 
sun’s distance and position in the sky, whether or not 
the quantitative explanation of this normal variation is 
entirely satisfactory. There is no suggestion of any 
normal diurnal or seasonal variation of the output of 
solar energy which would account for any part of the 
normal variation of global weather. This is entirely a 
question of the regularly variable distribution of the 
solar energy. 
As soon as a comparison is made between the irregu- 
lar, anomalous fluctuations of world weather patterns 
and the irregular variability of the output of solar 
energy, the evidence of definite relationship between 
the highly complex variations of these two patterns 
of change becomes at many points contradictory, in- 
decisive, and highly controversial. In our present state 
of ignorance as to (1) the specific nature and amount 
of the solar energy changes, (2) the specific effects 
which this irregular solar activity produces in the higher 
atmosphere, and (3) the mechanism of interaction be- 
tween the higher and the lower atmosphere, it is quite 
impossible conclusively to prove or disprove the effec- 
tive influence of irregular solar energy variations on the 
anomalous fluctuations of the global weather patterns. 
The evidence for this influence must inevitably depend 
to a large extent on inference and on the elimination of 
possible alternative explanations of observed effects. 
Such evidence is of necessity somewhat subjective in 
character, and liable to some stretch or strain in its 
interpretation. In the following discussion an effort 
will be made to maintain objectivity in the presentation 
and judgment of the evidence, but the interpretation is 
intended to be sympathetic to the view that irregular 
solar activity is the primary factor in the control of 
anomalous weather fluctuations. 
To facilitate the presentation of irregular solar ac- 
tivity as the predominant factor in controlling the 
anomalous fluctuations of weather and climate, the 
following discussion is divided into three sections, as 
follows: 
1. The nature, periodic character, and observed 
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effects in the higher atmosphere of irregularly variable 
solar activity, which presumably is causally related to 
anomalous weather fluctuations. 
2. The periodic character and geographical pattern 
of anomalous weather fluctuations, which are presuma- 
bly related to variable solar activity. 
3. The applicability of variable solar activity as the 
primary explanation of anomalous weather fluctuations. 
THE NATURE AND PERIODIC CHARACTER OF 
VARIABLE SOLAR ACTIVITY 
Systematic studies of the sun have revealed several 
characteristic features that vary semicyclically. It is 
the purpose of this section to discuss briefly these 
features, their variations, and the observed effects of 
the variations on terrestrial phenomena. The only book 
devoted exclusively to a technical discussion of the sun 
is that of Abetti [1]. A more recent semipopular book is 
that of Menzel [15]. Various astronomical texts, for 
example [2] and [19], give brief discussions of the sun. 
The sun’s visible surface, or pholosphere, presents a 
mottled appearance on telescopic inspection. Many 
small brilliant granules can be detected against a darker 
background. Sunspots and faculae are much larger and 
more stable features of the solar surface. The sunspots 
are relatively dark areas, roughly circular in form. 
They usually occur in groups, dominated by two large 
spots. The individual spots vary in diameter from a few 
hundred miles to tens of thousands of miles. Faculae, 
on the other hand, are relatively bright areas, usually 
occurring in the vicinity of sunspot groups. 
The spectroheliograph photographs the sun in the 
selective radiation of one element, and hence enables 
us to study the sun at levels above the photosphere. In 
both calcium and hydrogen light, large bright (relatively 
hot) or dark (relatively cool) patches are observed, 
especially in the vicinity of the sunspots. These are 
called flocculi. When the hydrogen flocculi are carried 
by the sun’s rotation to the solar limb, they appear as 
bright prominences, or projections of gas from the sun. 
At times very intense outbursts, called flares, occur. 
These flares are accompanied by hydrogen emissions 
detectable at the wave length of the Ha line in the 
visible part of the solar spectrum. Another solar phe- 
nomenon, recently noted by Roberts, is the occurrence 
of spicules. These are relatively small and relatively 
short-lived extensions of gas from the chromosphere, 
and are most noticeable at high solar latitudes. 
Even farther out from the photosphere is a very 
