822 
phenomena such as the alternation between meridional 
and zonal circulation in the Northern Hemisphere (see 
p. 827) and the southern oscillation in the Southern 
Hemisphere. However, these regulatory phenomena 
merely shape the macrometeorological events and can- 
not be regarded as governing complexes of conditions. 
If they alone were decisive, obvious periods should 
occur in the course of the weather, whereas in reality 
one must search for such periods by means of “methods 
for the discovery of hidden periodicities.”” The solution 
of the second fundamental problem is given by the 
empirical facts briefly sketched in the two preceding 
paragraphs from which the following conclusions can 
be derived: 
FourtH Empirican THrorem: The fluctuations in 
the solar radiation represent complexes of conditions that 
govern the course of the large-scale weather. 
WEATHER FORECASTING 
for the latitudes 50°N, 60°N, and 70°N, where R is the 
mean radius of the earth, ¢ is the latitude, and |Ap|, 
is the pressure difference from one extreme value to the 
next along a latitude circle. The mean zonal air motion 
(eastward and westward) is expressed by the mean of 
the meridional pressure gradients at sea level from 40°N 
to 75°N, averaged over all meridians, 
_ 1S = |Apls 
Mo —75 a > L 5) 
where Z is the length of the meridional distance be- 
tween 40°N and 75°N, | Ap |, is the pressure difference 
from one extreme value to the next along the meridian 
between 40°N and 75°N, and n is the number of merid- 
ians for which | Ap |, is computed [22]. It should be 
noted that the mean gradients were first determined 
for each single day and the monthly means computed 
Tasie II]. Montaty Means or tHE Datty Zona aND MERIDIONAL PRESSURE GRADIENTS IN THE NORTHERN HEMISPHERE 
Zonal pressure gradients* (mb per 1000 km) Bae eee eee 
Month 
1937 1938 1939 1937 1938 1939 
50°N. 60°N 70°N 50°N 60°N 70°N 50°N 60°N 70°N 40°-75°N 40°-75°N 40°-75°N 
January Mey eee ee 10.7 12.4 10.5 | 10.7 | 10.5 | 12.0 11.5 11.1 
Kebruany 2 Ae cact oon ee 10.5 11.8 10.5 12.2] 11.9] 8.9 10.7 11.9 
IMLS Sig dea eaomeieiy slg aaa ict SeENGIn A ot 10.6 10.6 9.8 | 10.8) 9.7 10.6 10.3 
/ Navn Ee, Meh eo trees cae Bet eeors et net Bes 5 8.8 10.2 9.8 8.8 | 10.4 8.9 9.8 9.0 
IMIR VeR Ree. heck Gee ee 8.0 9.0 8.1 73 || SY 7.6 8.2 7.8 
pI UUaNee Revoeaty nett ce aint roe argcatan 6.9 7.6 7.4 6.8 | 7.5 | 7.4 7.2 7.0 
Tillivie cette teeeictebaten Gaeliien 6.0 7.0 eS 6.1 | 7.3) 7.0 6.4 6.5 
MURR aha na ralele ae 6.0)| 7.4) 7.91) 6.2) | (8) | Ges) 7.8 8.1 
Septembarcd) Wem. Memniie 6 7.8| 10.0] 9.6] (8.0) | 9.8) | @.0) 8.6 9.0 
October Teen cee ee ae tind 9.0 | 10.3 | 10.0] (8.7) | 1.8) | (12.7) 9.6 10.8 
INOWeri be ae ean Msi) TLS || 10.7 |) @O.i) | CB hy | @a,0) 10.3 11.5 
December. ee 11.2 | 12.3 | 9.4 | (11.2) | (12.2) | (43.1) 10.5 11.8 
Wien CAws, UCR aulby IBID). ccnescesscancoscescnovanavnssvaagcoeasauan 8.8 | 10.1) 9.5 a4! 
Mean (50°N=f02N) TL Bie, SY Sie TSO NE rs SE DS ee een 9.5 
* Numbers in parentheses are uncertain. 
Therefore, an intensive promotion of solar physics 
is one of the prime prerequisites for progress in long- 
range weather forecasting. 
Morphology of the Grosswetter. Forms of the General 
Atmospheric Circulation. Twenty years ago it was recog- 
nized that it is erroneous to consider the west-east cir- 
culation as the essential feature of the “general atmos- 
pheric circulation” in the temperate zone [8; 33, pp. 
215-218]. Without the meridional movements there 
would not be the exchange between the warm sub- 
tropical and cold polar air masses that is the most 
important effect of the general circulation in the tem- 
perate zone. The quantitative equivalence of zonal 
and meridional circulation in the lower troposphere is 
shown in Table III. Here, the mean meridional air 
motion (poleward and equatorward) is expressed by the 
mean of the zonal pressure gradients at sea level, 
z |Apla 
AO) = 2Rr cos ¢’ 
from them afterwards. Comparison shows that the 
differences between the mean zonal and the mean 
meridional gradients by months are much less pro- 
nounced than the seasonal trend of both these indices. 
Sometimes, however, large differences between these 
indices occur on individual days. Thus the mean zonal 
gradient at 60°N amounted to only 8.5 mb per 1000 
km on January 11, 1949 but, on the same day, the 
average of all meridional gradients from 50°N to 65°N 
was 15.0 mb per 1000 km. The mean gradient for 
meridians with west-east zonal circulation only, be- 
tween 50°N and 65°N, (that is, two-thirds of all merid- 
ians on that particular day) was 17.5 mb per 1000 
km. Table IV shows the pronounced daily fluctuations 
of the circulation in addition to the seasonal trend. 
On some winter days, values are observed that almost 
equal the summer normals and on many summer days 
the gradients correspond closely to the mean values of 
winter. 
The recently available daily cireumpolar 500-mb con- 
