GROWTH OF CLOUD DROPS BY CONDENSATION 205 
bers of droplets of all sizes near the cloud base in 
the Trade-Wind Cumulus Case than in the Cumu- 
lonimbus Case (Fig. 17). Table 2 shows the rela- 
tive values at two corresponding levels above the 
cloud base. The modal sizes for the Trade-Wind 
Cumulus Case are taken from the differential 
frequency curves in Figure 18. 
At 130 m above the cloud base the trade-wind 
Cumulus has more drops in all size groups larger 
than four microns than the Cumulonimbus. How- 
ever, because of the larger number of small nuclei 
which are activated, the mode is smaller even at 
this height. By 800 m above the cloud base this 
greater competition for the available liquid has 
resulted in smaller numbers of drops larger than 
nine microns in the Cumulus Case than in the 
Cumulonimbus, and a modal size of eight microns 
as opposed to 11. At the top of the trade-wind 
cumulus the modal size is 11 microns, and there 
are about ten per liter greater than 20 microns 
in radius. Thus it would appear that also in this 
case precipitation initiation by the warm process 
129 ———_+— -—}— - — 
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108 10° 10° 10° 10? 10'cm 
oo! oO! 10 10 100 1000 microns 
Orop Radius 
Fic. 14—Differential drop-size distributions after 
various elapsed times, Cumulonimbus Case 
10! 
Liquid Content 
7.20.10 micron 
10° 10° 
10" a 
7 
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10 
1200 1800 2400 3000 3600 
Time (Seconds) 
Fic. 15—Variation of liquid content and visual 
range (for light of wavelengths 4000 and 7000 A), 
Cumulonimbus Case; thin lines show liquid con- 
tent in various drop-size groups 
could be expected, with the possibility of light 
showers reaching the sea surface. 
The liquid content in the Trade-Wind Cumulus 
Case (Fig. 19) increases faster than in the Cumu- 
lonimbus Case, and the visual range decreases 
more rapidly. The values at corresponding heights 
above the cloud base are shown in Table 2. The 
maximum liquid content in the trade wind Cumu- 
lus, however, reaches only 2.7 grams per m’, less 
than one-half that in the Cumulonimbus, because 
of the continued ascent in the latter case, but the 
minimum visual range is a little lower because of 
the larger total number of activated droplets in 
the Trade-Wind Cumulus Case. 
Because the 0.032 micron group is activated in 
