EXTENDED-RANGE WEATHER FORECASTING 
tour charts show that a remarkable meridional cireula- 
tion extends also to the upper troposphere of the middle 
latitudes. Even at the 5- and 10-km levels, there is, 
Taste LV. Darty VaLuEs oF THE MrAN ZONAL GRADIENT 
ALONG THE 60°N Larirupr Crrete DuRING THE FIRST 
Stix Monrus or 1949* 
(In mb per 1000 km) 
Day January |February| March April May June 
1 el 13}.7/ S35 il 7.0 10.8 7.3 
2 12.6 10.2 13.1 8.1 1.3 9.1 
3 9.4 10.7 12.4 11.1 9.5 8.6 
4 12.6 13.2 13.7 ITE) 8.8 G9 
5 12.6 12.7 138.7 11.4 Ua 8.5 
6 10.6 13}. 10.1 @).7/ 10.6 7.0 
7 iil 5a 11.2 12.5 9.1 1.2 6.4 
8 15.5 13.9 14.0 9.0 7.4 7.6 
9 alsyal 9.2 10.5 10.0 9.0 7.8 
10 9.9 13.5 10.0 | 12.4 8.1 7.3 
11 8.5 13.6 11.3 9.9 7.9 6.9 
12 10.5 11.8 12.1 7.8 10.0 8.2 
13 7.4 10.4 12.3 7.9 8.2 8.0 
14 7.3 9.0 11.6 Gell 8.0 7.4 
15 10.5 10.3 11.9 6.4 1.2 8.1 
16 11.3 11.6 12.7 7.4 9.1 11.7 
17 12.8 12.4 11.9 8.1 10.7 10.4 
18 13.4 | 14.8 15.3 8.8 9.4 11.6 
19 13.4 | 13.9 16.0 8.9 eX 9.5 
20 11.3 It. 7/ 10.8 6.5 6.3 8.3 
21 14.5 12.0 10.3 7.6 8.2 7.4 
22 17.6 | 12.8 11.0 | 10.5 8.0 7.2 
23 14.3 8.8 12.0 8.3 8.2 7.4 
24 14.0 8.7 Qi Qi 8.4 9.1 
25 13.2 10.8 10.2 9.9 10.0 6.9 
26 11.9 9.8 9.0 8.5 8.2 8.4 
27 11.9 10.7 8.7 8.3 8.1 (0) 
28 11.6 | 13.8 Cot 7.8 | 10.2 4.3 
29 13.1 8.5 7.4 8.6 8.2 
30 15.6 1.2 8.1 8.7 Uae 
31 15.9 Toll 9.0 
Monthly 12.3 11.7 11.3 8.8 8.6 7.0 
means 
_ * The principal maxima are in boldface; the principal min- 
ima are in italics. 
only in exceptional cases and then at the most as far 
south as 55°N, an uninterrupted west-east circulation 
around the pole (Fig. 5). In most cases, the isobars at 
the 5-km level seem to “meander” (Fig. 6), the pole- 
ward convexities representing warm ridges, the pole- 
ward concavities representing cold troughs [52, 53). 
The sinuosities of the isobars are called waves by 
some meteorologists. One can, however, argue that this 
designation is misleading because it is suggestive of 
progressive waves. Experience has taught us that the 
ridges and troughs at the 5-km level are, in general, 
rather stationary with respect to their geographical 
longitude (as in Figs. 7 and 8). Zonal movements occur 
principally when two pressure ridges on either side of a 
trough join on the poleward side of the trough thereby 
cutting off a low-pressure cell, or when two troughs on 
both sides of a wedge join on its equatorward side thus 
cutting off a high-pressure cell. In some cases there may 
be longer zonal movements of individual pressure cen- 
ters in the upper troposphere. An impressive example of 
823 
such a case is the high-pressure cell at the 5-km level 
that within five days (November 24-29, 1949) moved 
from 70°N and 172°W to 78°N and 55°W along an 
on 
RSE os 
Ry ae 
Fre. 5.—Contours of the 500-mb surface (in tens of dynamic 
meters) for January 11, 1949 at 0200 GMT. Example of a cir- 
cumpolar zonal circulation. 
unusual path. This is also an example of the fact that 
relatively warm anticyclones in the upper troposphere 
can occur at rather high latitudes even during the 
i SS 9 
Ure PN \ fi LAA : 
// 
| 
y : 
R No 
7 
Uf: 
y 
580 
= 
7 
20° toe oe toe 
Fie. 6.—Contours of the 500-mb surface (in tens of dy- 
namic meters) for June 23, 1949 at 0200 GMT. Example of a 
circulation in the form of elongated meridional circulation 
cells (Zirkulationsstreifen). 
winter season. (Regarding zonal displacements of 
wedges and troughs, see p. 830.) 
The centers of high- and low-pressure cells at the 
5-km level for the period from June 21 to July 5, 1949 
are shown in Fig. 7. In each of the regions marked I and 
III there is a moving low-pressure center (the one of 
region III splits at times). Regions II and IV each con- 
tain a high-pressure center and show, in particular, the 
small zonal displacement. On June 27 and 28, a stronger 
zonal movement occurred. to the northeast for region 
