6 TOR BERGERON 
thing is going on in the lower troposphere as far 
as the precipitation amount is concerned. Also 
other forms of precipitation are important to 
study: especially those that give unexpectedly 
small amounts, for example, smaller amounts 
than one would expect under conditions that 
generally would guarantee a substantial rain. 
One has hitherto distinguished between micro- 
physics, macrophysics, and synoptics of clouds. 
However, I think it would be better to use the 
terms micro-, meso-, and macrophysies (corres- 
ponding roughly to cloud particles, individual 
clouds, and cloud systems) since the name ‘syn- 
optics of clouds’ introduces an asymmetry, and 
since one is apt to think that ‘micro’ and ‘macro’ 
are for us, but ‘synoptics of clouds,’ that is for 
the weathermen, so we will not bother with 
= 
x NS 
that. In fact, these things hang so intimately 
together that they cannot be solved separately. 
We must all collaborate with these problems. 
Then, another point that I believe is impor- 
tant. Every cloud or cloud system giving abun- 
dant rain or snow can be divided into a releasing 
part and a spending part. I call it the releaser 
and spender part of the cloud or cloud system, or 
the ‘seeder’ and the ‘feeder.’ They may not even 
form parts of one and the same cloud; they may 
be two different clouds, one above the other, co- 
operating in some way or other; and they must 
really cooperate in order to insure efficient pre- 
cipitation. A cloud without a spender will give 
very little or no precipitation. A cloud without a 
releaser will generally give no precipitation at 
all, or only drizzle, even if the condensation is 
Cunb cap 
ASTON x 
rie me Ch, 
= ee ES AB 
4s Cloud and precipitation ==> Air-current at heat 
source 
«eee lce-nucleus level 
al Isobar 
==> Air-current at heat 
sink 
Fra. 1—Main precipitation mechanisms; schematic vertical cross sections 
