SOLAR ENERGY VARIATIONS AND ANOMALOUS WEATHER CHANGES 
prevailing type of climate has been that of postglacial 
severity rather than mildness. The important fact about 
the postglacial period is that in the relatively short 
time of 8000 years the world climate has swung through 
two cycles of change which in amplitude are a sub- 
stantial part of the much longer typical glacial-inter- 
glacial cycle of the Pleistocene Epoch. 
Secular Fluctuations. These refer to cycles of change 
or trends of weather and climate which are completed 
within a single century. Examples are the so-called 
Briickner Cycle, the single or double (Hale) sunspot 
cycle, and the world-wide trend since 1880 towards 
higher temperatures which has progressed poleward 
and reached a crest in the higher latitudes during the 
past two decades. Many investigations of these secular 
fluctuations of the world weather pattern have been 
undertaken. Here it need only be mentioned that these 
fluctuations are small in amplitude compared with 
both the climatic and the geological fluctuations, but 
they do show notably similar characteristics as to 
latitudinal displacement of the zonal wind systems and 
prevailing storm tracks, and as to the corresponding 
severity of cyclonic storm activity in middle latitudes. 
This latitudinal shift of storm tracks and belt of maxi- 
mum cyclonic precipitation is shown quite clearly by 
the last, and statistically best-established, of Briickner’s 
rainfall cycles (1855-1885), by a number of Tannehill’s 
secular trend graphs of pressure, temperature, and rain- 
fall [24], by the trend since 1880 towards warmer and 
drier conditions in progressively higher latitudes, and 
by many of the double sunspot-cycle phase-change 
patterns of pressure, temperature, and rainfall (27, 28]. 
The basic similarity of the geographical patterns of 
secular changes and trends of weather anomalies to the 
patterns of climatic and geological changes is consid- 
ered to be highly significant for any physical interpreta- 
tion of these fluctuations. 
Anomalous Fluctuations. This class is made up of 
the anomalous irregularly cyclical fluctuations of the 
general circulation from week to week, from month 
to month, or from season to season within the year. 
Im recent years considerable synoptic and statistical 
analysis has been directed toward the determinat on 
of the essential character and the most significant param- 
eters for the diagnosis and prognosis of these fluc- 
tuating patterns of the general circulation. As a result 
of these studies there was developed the concept of the 
high- as opposed to the low-index pattern of the general 
circulation as an expression of the essential character 
of the opposite extremes between which the pattern 
typically fluctuates. These fluctuations usually run in 
cycles of from three to seven or eight weeks. During 
some periods the opposite type patterns reach more 
extreme development than during others, and during 
some seasons or years or even longer periods (secular, 
climatic, and geological) one type or the other is largely 
predominant. The most noteworthy feature of these 
two contrasting type patterns is that they are world- 
wide in character, so that they appear to express the 
operation of a mechanism of basic significance in all 
383 
of the longer-period fluctuations of the general circu- 
lation [17, 23]. 
Originally the single parameter by which the high- 
and low-index patterns of the general circulation were 
defined was that of the strength of the sea-level zonal 
westerly winds between latitudes 35° and 55°, but much 
statistical and synoptic analysis [18, 28] has indicated 
that there are other parameters which are probably 
of more significance. 
In the light of these statistical studies the change 
from a high- to a low-index pattern (the reverse of a 
change from low to high index) is best expressed by the 
significant parameters of the state of the general cir- 
culation, other than by a weakening of the sea-level 
zonal westerlies, in the following terms: 
1. An intensification and expansion of the polar anti- 
cyclonic circulations, with a corresponding equator- 
ward displacement of the zonal wind systems and the 
related climatic zones, notably of the zonal westerlies 
and the prevailing storm tracks. 
2. An intensification of the cellular (as opposed to the 
zonal) pressure and wind pattern. At sea level this 
trend is indicated by a splitting of the major cyclonic 
and anticyclonic centers of action, with a north-south 
rather than east-west orientation of the major axes. 
At upper levels the trend is indicated by an increased 
amplitude and shortened wave length of the trough- 
ridge pattern, with a tendency toward the formation of 
closed anticyclonic centers in the higher latitudes and 
closed cyclonic centers in the lower. The result is an 
increase of the latitudinal exchange of air masses, and 
of storminess and extreme air mass contrasts in lower 
middle latitudes. 
3. Initially an increased poleward temperature grad- 
ient in the lower troposphere in middle latitudes, hence, 
with the increased austausch, a marked increase of 
poleward transport of heat and energy. 
It is immediately apparent, from the above summary 
of the high-low index contrast, how strikingly this 
contrast of the general circulation pattern resembles 
the interglacial-glacial, and less extreme climatic and 
secular, contrasting world weather patterns. 
Daily Fluctuations. These are essentially the day-to- 
day progression of pressure centers, with related air 
mass and frontal phenomena, as observed on the daily 
weather maps. Essentially the daily fluctuations of the 
weather pattern are local rather than global in char- 
acter, for only relatively small-scale circulation phenom- 
ena can run through a cycle of change in a day or two. 
However, it must be recognized that the sum total of 
these small-scale fluctuations integrated over a period 
of days or weeks constitute the world-wide patterns 
of weather change discussed above as the anomalous 
changes. When the anomalous changes are progressing 
rapidly, the trend of this progression, and the contribu- 
tion to it of the daily local changes, becomes quite evi- 
dent. In particular, the progressive effects of any sud- 
den impulses (solar) to the anomalous fluctuations of 
the world weather pattern must be traced in daily 
pattern changes. Such effects are noted below in the 
reference to Duell and Duell’s study [6] of the effects 
