COALESCENCE TENDENCIES IN CLOUD DROPLET SPECTRA 189 
TaBLe 6—Values of T for the four cases parison between the two smallest categories of 
a ues — ] droplets and the number of existing, condensa- 
Distri- | 83 ae dros | n/E |p-=ay/iv/z) tlon-produced droplets which have a radius 
bution | 3S |with r = 27 roughly equal to that of the droplets produced 
~ by combining the two small droplets. Actually 
cn, al Sc07 Se it would be better perhaps to compare all coales- 
lee alov 3 ; 
et ae | 3x ine i . Ce cences between the smallest categories having a 
3.8 26. ; 
Ill 53x 105| 2.3 xX 102 1.3 % 193 ‘tadius not more than about ten per cent larger 
| 6.7 X 10 | 60. than the minimum value with the number of 
Il 100 | 4 X 105 
! | 
condensation produced large droplets. If this is 
done, values of T are decreased by a factor of 3 
those with a radius r = 2! = 1.26r in periods — to 5. 
ranging from less than one second for the dis- If these computations are made for a larger 
tribution Case I at 100 cm/sec to more than 1000 liquid water content then the collisions between 
sec in the distribution Case II at 5 cm/sec. These the small droplets become relatively more im- 
values for the four cases are given in Table 6. portant. To see how this proceeds a useful dia- 
The values for T in Table 6 only give a com- — gram can be constructed as in Figure 3. Here the 
7 = 
9 10 15 20 30 40 50 60 70 80 90 100 
(2%+Ar) 
Fic. 3—The number of potential collisions n’ per unit time between two size categories of droplets 
of radius (7) and (7 + Ar) as computed from Eq. (13); as 7 increases the points in the curves move along 
the diagonal lines (rkNiN2Ar = constant) hence tend to line up vertically as Ar/7 + 0 and thus demon- 
strates the increasing importance of collisions between the smaller size categories as 7 increases with 
time or liquid water content; curve AB becomes A’B’ as 27 + Ar increases; the curves marked C and 
D represent two cases computed in Table 6 and demonstrate how different the collision expectancy can 
be for the different condensation conditions assumed. 
