12 TOR BERGERON 
sure jump’ of another case with similar charac- 
teristics: June 1-2, 1951. Figure 4 shows his 
isochrones of this pressure jump over Nebraska, 
Towa, Kansas, Missouri, and Oklahoma; thus it 
covered quite a vast region. After having studied 
the numerous barograms from this case, I do 
not doubt the reality of this pressure Jump; 
although, naturally one needs not accept the 
various explanations given. In the United States 
there exists a wonderful network of pluvio- 
graphs, and their registrations have been worked 
up and published in the shape of hourly precipi- 
tation data, this being the only country in the 
world that has done anything similar. With the 
aid of these data, I was able to analyse, in 
1953, a series of maps, of which Figure 5 shows 
a sample. As you see, the results are similar to 
those reached by Dr. Fusrra in 1955, so our 
works corroborate each other quite nicely. In 
this ease there was a long quasistationary Polar 
front, with a cold-front section extending to- 
wards SW over Kansas. The warm-front section, 
over Nebraska and Iowa, gave only weak rain. 
At the top of the warm sector within the Tropical 
air, in SE Nebraska, there was, however, a 
circular convective system with intense rain 
along its outer edge, but with very little or no pre- 
cipitation in the interior, and a small High at the 
Meon temperature for September 
Meon temperoture for February 
Temp. of adiabatic lifting with 
28°C and 85% RH. of seo-level 
Temp. of adiabatic lifting with 
25°C ond 85% R.H. af sea-level 
% Lability energy in September 
Lobility energy in February 
Fra. 6—E. Palmén’s general hurricane tephigram 
for the Caribbean Sea 
very center. All this could be traced by means 
of the above-mentioned hourly precipitation 
data. The maps also show the position of the 
pressure jump taken from Dr. Tepper’s map 
(Fig. 4). 
We do not know for certain the origin of 
convective systems; but they generally form in 
the warm sector, and often at its top. Some- 
times the ‘squall line’ is parallel to the cold 
front; but in such a case as this, with a circular 
pseudo-front, I am not able to accept the old 
explanation that a ‘squall line, or convective 
system, should be caused by the overflowing of 
cold air at a higher level. Then, why does it not 
extend down through Texas in this case? In fact, 
the explanation of the convective system may be 
quite another one in this case, and we are on the 
safe side if we start by observing it, then digest 
and carefully analyse it, and save our explana- 
tion for a later stage. What I wanted to under- 
line here is that the pressure jump at the stage 
of the 00h 30m z map (Fig. 5a) les far behind 
the ‘squall line’ and also behind the cold front. 
Whereas, nine hours later (Fig. 5b), the pressure 
jump has mostly overtaken both the ordinary 
cold front and the pseudo front. The convective 
system now forms an almost circular rain area, 
with hardly any rain at the center. On later 
maps, the pressure jump even went further into 
the Tropical air and left both the ordinary cold 
front and the pseudo front behind it. Thus, one 
may conclude that in this case the pressure jump 
was produced, neither by the ‘squall line,’ nor by 
the cold front; they were in this case three more 
or less independent agents. Certainly, these phe- 
nomena are worthy of many more investigations 
in the future. 
PatMéN has shown that the tropical hurri- 
canes form and are maintained according to the 
convective theory. In Figure 6 the curve of con- 
vective lifting, in February, when there are no 
hurricanes, lies mainly to the left of the curve of 
stratification. The corresponding curves for Sep- 
tember, in the middle of the hurricane season, 
show that there is then a great positive area be- 
tween the curve of lifting and the curve showing 
the stratification of the air. What I especially 
wanted to emphasize is that the curves of lifting 
diverge with height. Thus, a certain difference of 
temperature at the Earth’s surface corresponds 
to a two or three times greater difference of 
temperature at the tropopause, or say at the 
300-mb level. This implies that a surplus of 
2°C in the rising air at the cloud base will give 
