200 
NEIBURGER AND CHIEN 
3 
Ttelsitinn) 
ti titi 
Liquid Content— 
1 
= 010 micron 
0 
| 
| 
‘of 
Sane eel 
Liquid Content (Grams m7>) 
fo} 
03 
Visual Range (Meters) 
y-Nisual Ronge 
2000 3000 
Time (Seconds) 
4000 5000 
Fie. 7—Variation of liquid content and visual range (for light of wave- 
lengths 4000 and 7000 A), Stratus Case A; thin lines show liquid content in 
various drop-size groups 
and eight microns, and 360 between eight and 14 
microns. 
The rapid development of the visual cloud is 
shown by Figure 7, in which the visual range com- 
puted from Koschmieder’s formula and the liquid 
content are shown as a function of time. The 
visual range drops from 5 km at 2400 see to 50 m 
at 3000 sec, a change to one per cent of its earlier 
value in ten minutes. In the same interval the 
liquid content increases from 3 X 10-4 grams per 
m*, to 0.3 grams per m*, a factor of one thousand. 
In the unrealistic conditions postulated (rapid 
cooling and no fallout) the visual range drops 
below ten meters and the liquid content rises al- 
most to three grams per m*. The thin curves in 
Figure 7 show the contributions of the various 
size groups to the liquid content. Almost all of 
the liquid content is due to the 0.1 micron and 
0.32 micron groups, with the former accounting 
for about five-sixths and the latter about one- 
sixth of the total. This is because the larger nuclei 
are so much less frequent and the more frequent 
smaller ones do not grow. 
The growth curves in Stratus Case B, in which 
the same cooling rate was used but with many 
more large nuclei, are shown in Figure 8. Satura- 
tion with respect to a plane water surface is 
reached a little later than in Stratus Case A, the 
peak supersaturation attained is slightly lower, 
and the amount of supersaturation remains lower 
throughout the drop growth. However, there is 
very little change in the rate of growth of the 
various-sized drop groups, so that the change in 
the humidity curve reflects almost entirely the 
additional water required by the growth of the 
larger number of large drops. 
