PROBLEMS AND METHODS OF RAINFALL INVESTIGATION 9 
rather intense. And that is again a reason why 
our problems cannot be solved by micro-, meso-, 
and macrophysics of clouds working separately. 
I am now going to discuss some important 
types of precipitation and their mechanisms. 
Figure 1 tries to show schematic vertical cross 
sections of the main mechanisms of cloud and 
precipitation (excluding the drizzle from fog 
and Stratus) ; and by chance the size of the dif- 
ferent small pictures roughly corresponds to 
their relative importance on the globe—The 
second row shows the convective system, which, 
together with the ordinary convective clouds of 
the first row, gives the better part of the pre- 
cipitation in tropical regions, and even in middle 
latitudes on land in summer. Correspondingly, 
over the middle-latitude oceans, the convective 
clouds give the bulk of the winter precipitation. 
(In the Middle West, where the convective sys- 
tems or ‘squall-lines’ bring most of the spring 
and autumn rains, the warm-fronts then seem to 
bring relatively small amounts of precipitation.) 
—The third row contains the opposite kind of 
mechanism, the tropical hurricane, which brings 
great amounts of precipitation on the oceans and 
adjacent coasts in late summer and fall. In this 
figure there is an outward similarity between the 
convective system and the tropical hurricane, 
but at the same time they are opposite. Here 
I only want to point out that they contain two 
‘circulation wheels’ each, a big one C,, and a 
smaller one C, that is caused by the rainfall 
cooling. If they cooperate, as within the tropical 
hurricane, a very efficient mechanism is set up 
producing a cyclonic vortex, often with ex- 
tremely low pressure at the center. In the con- 
vective system, on the other hand, these two 
circulations counteract each other; Cy, causes a 
WM VOns.21 csAV gs 
SS 
PASO A 
20 
Mo. 
Texas ! 
| 09z 
: > 03z Isochrone of pressure jump, 
35°N ' 2 after M. Tepper 
+05mb Okla +10 ——- Equiscalar of pressure jump 
100° W 2 95° amplitude in mb 
1 n Ll ! 1 =a L ! ai 
Pressure Jump 
1-2 June 1951 
Fria. 4—Isochrones of the pressure jump of June 1-2, 1951, according to M. Tepper 
