840 
demonstrated by graphing the number of days of oc- 
currence of extreme meridional flow types (D, A, Bn-c) 
in the winter season (December, January, and Feb- 
ruary) for each year. This appears as the middle curve 
in Fig. 2. The curve for the extreme zonal flow types 
(Eu, Em, Ex) is the top curve in the figure. These 
curves show quasi-periodic variations with a period of 
five or six years and an appreciable amplitude. The 
two curves are out of phase. 
The period is suggestive of half the sunspot cycle, 
and the curve of sunspot annual relative numbers is 
shown at the bottom for comparison. The sunspot 
curve is based upon the annual value corresponding to 
the year of the January and February portion of the 
plotted winter-season type characteristics and hence is 
in effect somewhat lagged in phase from the top two 
curves. The correspondence between the peaks in the 
extreme meridional flow types and the sunspot maxima 
and minima is striking. 
PROSPECTS FOR THE FUTURE 
With regard to prospects for the improvement of 
techniques for extended-range forecasting, it is the 
author’s opinion that two fields of investigation offer 
the most attraction. One of these is the study of the 
long-period interaction between broad-scale circula- 
tion features in different parts of the Northern Hemi- 
sphere and, for that matter, over the whole world. 
This, it would appear, involves the modes of energy 
dispersion. A joint theoretical and synoptic attack is in 
order. 
The other field involves a thorough study of the 
radiational properties of the earth and its atmosphere 
and the study of the effects of variations in solar 
output upon atmospheric motions. The example of a 
general relationship between solar activity and 
weather-type frequencies presented above is just one 
of many such relationships developed from studies of 
weather types. The works of Abbot, Clayton, and 
many others provide evidence favoring a real relation- 
ship. Meteorological events, seemingly inexplicable 
from the viewpoint of a closed system consisting of 
the atmosphere and the earth, are continually occur- 
ring and require a systematic investigation of extra- 
terrestrial effects. 
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