GROWTH OF CLOUD DROPS BY CONDENSATION 
TaBLe 2—Comparison of relative values at corre- 
sponding levels above cloud base for the Cumulo- 
nimbus and Trade-Wind Cumulus Cases 
Distance above cloud base 
Item | 
130 m 800 m 
Cloud type Cb Cu Cb Cu 
Time of rise, sec 1300 900 1800 1200 
No. of drops per 
em? larger | 
than: 
20 microns 9X PSE AN bee Ga [ne eg 
10-6 10-4 O54, |) L0e3 
14 microns | 1.7 X 6 xX 9X | 5X 
10-4 1078 10-3 | 10-2 
Symicrons, | 15 $< | 14 || 158 100 
10-2 1071 
4 microns 220 570 | 200 550 
1 micron 350 680 | 310 620 
Modal size, mi- 5.4 4.3 11 8 
cron 
Liquid content, 0.29 0.4 | ilke7/ 2.6 
g/m$ 
Visual range,m | 45 30 15 8 
AEM 
10° 4 
* t*600 sec 
3 1 i a sec 
s 10 a ~ Ni SoD sec zimra eal 
3 XN i eal 1200 sec 
5 rT aN iy eee 
2 tn lif 
fF t 
= ol . 4 
° at aH 
& F an 
> Np | Ii 
' 10" + Li 
a: } 
o 1 
aE 
E i; + |! + 
8 £F \hh | 
e 10° \ 
° F | i 
| \\ 
E \\\ 
‘ " 
10 —\,\\ + 
FE hak | 
- /\ \N\ | 
A Pere 1 \ feeeurn| 
10® 10° 10° 10° 107 10'cm 
0.oO1 oO! 10 10 100 1000 mrom 
Drop Radius 
Fic. 18—Differential drop-size distributions af- 
ter various elapsed times, Trade-Wind Cumulus 
Case 
— 
os 
Liquid Content (Grams m~>) 
Visual Range (Meters) 
af 
900 1200 
Time (Seconds) 
10° 
'800 
1500 
Fie. 19—Variation of liquid content and visual 
range (for light of wavelengths 4000 and 7000 A), 
Trade Wind Cumulus Case; thin lines show liquid 
content in various drop-size groups 
tribution has the modal radius somewhat larger 
than the observed distributions, and in the 6000- 
sec distribution the modal radius is more than 
twice as large as the observed modes. An explana- 
tion of the difference probably lies in the rapid 
rate of cooling assumed in the computations. The 
coastal stratus forms by slow cooling, during 
which the large drops may tend to settle out of 
the cloud. Another factor which may contribute 
to the small modal size in the observed distribu- 
tions is the fact that the observations were made 
in the daytime, when the clouds were tending to 
dissipate. 
While the initial nucleus distributions and ver- 
tical velocities used by Howell were quite differ- 
ent than those we used, his results are quite simi- 
