GROWTH OF CLOUD DROPS BY 
1003 
100 2 = ———IE : | 
100.1 
100.0 
100 
Humidity (%) 
Relative 
x @ wo 
ooo 
CONDENSATION 201 
fo) 
55 
Radius (cm) 
1034 
3000 4000 5000 
Time (seconds) 
Fic. 8—Variation of relative humidity and growth curves for various 
ity g 
drop-size groups, Stratus Case B 
In Case B, in order to determine more closely 
the separation between the nuclei which do not 
grow and those which are ‘activated,’ an addi- 
tional group was inserted, with average equiva- 
lent radius of nucleus 0.056 micron. It turned out 
that this group also was activated, so that the 
boundary between non-activation and activation 
for this rate of cooling lies between 0.032 and 
0.056 micron. 
In Figure 9 are shown the cumulative distri- 
butions for Case B. As might be expected, the 
main difference between these and those for Case 
A lies in the ‘tails’ of the curves, representing the 
largest drops. Thus at 3000 see the number greater 
than four microns is 330 per em’ compared with 
300 in Case A, but the number larger than ten 
microns is 230 per liter, compared with ten per 
liter in Case A, and 2.3 per liter are greater than 
20 microns. At 6000 sec about 50 per liter are 
greater than 20 microns in radius, compared with 
one per liter for Case A. Since in light rain there 
may be from two to 60 raindrops per liter, it will 
be seen that for the cooling rate assumed the 
Type B nucleus distribution might be expected 
to produce drizzle or light rain within a short 
time (from 5 to 50 minutes) after the cloud 
formed. 
As in the cumulative frequency curves, the 
differential frequency curves for Case B (Fig. 10) 
show little difference from those of Case A except 
that the tails show the larger number of large 
drops. The modes are nearly the same. Similarly 
the visual range and total liquid content curves 
are almost identical (Figure 11), since the larger 
drops are not sufficiently numerous to affect them. 
The bulk of the liquid content is due to the same 
range of sizes as in Case A, but the subdivision of 
this range into an additional group emphasizes 
the fact that the 0.1 micron group is responsible 
for the bulk of the liquid content even though 
