50 AIR MASS ANALYSIS 
Atlantic and Pacific for example; they are 
notable in spring in eastern U. S., too. 
The existence of “‘dynamic’’ lows and highs 
does not refute any principles of frontal or 
air mass analysis, however uncertain the the- 
oretical explanations, but such phenomena 
must be recognized as additional processes to 
be given due consideration in forecasting. 
It might be added that the semi-permanent 
sub-tropical anticyclones (e.g., Azores High) 
are also warm and dynamic in character; 
the moving anticyclones of middle latitudes 
often finally merge into them. However, the 
Aleutian and Icelandic semi-permanent Lows 
are more statistical than dynamic, due to fre- 
quent frontal cyclogeneses, though deep dyna- 
mic lows often stick there for days at a time.— 
R. G. Stone. 
The réle of the tropopause in the dynamics of extra-tropical disturbances 
“J. Bjerknes has especially studied the in- 
teraction between waves in the Polar Front 
surface and waves of the tropopause, showing 
that the latter cannot be the primary ones. 
According to J. Bjerknes these induced tropo- 
pause waves mainly consist in a horizontal 
meridional oscillation of the air at the oblique 
tropopause. 
E. Palmén adds to the above effect also the 
pumping effect of cyclones and anticyclones 
to which the stratosphere is subjected, using 
aerological data to show that the tropopause 
is often lower, the stratosphere temperature 
higher, in deep cyclones of our latitudes than 
in Arctic regions in winter. Such a state 
could not be attained merely by advection of 
the low and comparatively warm Arctic strato- 
sphere, but the stratosphere must also be 
sucked down by the cyclonic vortex (and by 
analogy pushed up in anticyclones). 
The author then proposes the following solu- 
tion, which takes account of both effects and 
also satisfies the well-known statistical data 
from the upper air of Dines and Schedler. 
The suction effect of Palmén ought to pre- 
dominate during and shortly after the most 
intense processes of cyclogenesis or anticyclo- 
genesis (‘‘Verwirbelung’’*=the transformation 
of a frontal wave into a vortex), when the 
suction effect of the ‘‘circular vortex’ (ac- 
cording to V. Bjerknes, 1921, sinking in 
cyclones, lifting in anticyclones) will be most 
pronounced and a “‘new tropopause” has not 
yet had time to form at the normal height.— 
The advective effect of J. Bjerknes, on the 
other hand, will most likely predominate not 
only during the initial wave-like stage of 
Polar Front disturbances but also during their 
final stage, when the violent pumping effect 
of the ‘‘Verwirbelung’? may have developed 
a kind of free oscillations of the tropopause, 
which liberate themselves from the tropospheric 
vortex and are propagated in the ordinary 
way eastwards.—These initial and final stages 
are of much longer duration and are also pre- 
dominant in intensity as compared with the 
stage of ‘‘“Verwirbelung” in those rather low 
latitudes from which the statistical data of 
Dines and Schedler were collected. This may 
explain why the statistics quoted speak in 
favour of the advective effect, whereas the 
intense high latitude cyclogeneses studied by 
Palmén show all the characteristics of the 
suction effect.”—T. Bergeron. 
VIII. 
In order to forecast local showers 
and thunderstorms successfully it is 
necessary to interpret aerological 
data in the light of a reliable analysis 
of the synoptic chart. An individual 
sounding made in the lower tropo- 
sphere is more immediately signifi- 
cant in summer than it is during the 
winter months. That is, in the warm 
months upper-air conditions imme- 
diately above a station are relatively 
important in determining the weather 
for the particular day, whereas in 
winter the rapid advection of air 
masses may so completely change the 
upper-air conditions over any given 
point that an attempt to forecast 
solely from the data in one sounding 
THE TEPHIGRAM* 
would be fruitless. Because of this 
control of the weather by local upper- 
air conditions, forecasters now con- 
sider upper-air soundings almost in- 
dispensable in summer work. In order 
to portray most effectively the state 
of the upper atmosphere, particularly 
from the standpoint of energy trans- 
formations, several diagrams have 
been suggested. 
Hertz developed a diagram (later 
modified by Neuhoff) on which an aero- 
*The procedures with the tephigram de- 
scribed herein may be readily applied to other 
thermodynamic diagrams such as the modified 
pseudo-adiabatic charts of the U. S. Weather 
Bureau (Upper Air Map C and forms 1147 
and 1126 Aero.) described in Article III, p. 18, 
to the Refsdal emagram and ‘“‘Aerogram’’, 
and to the Neuhoff diagram. 
