342 
16 32 48 
17.6 
16.0 
14.4— 
12.8 
HEIGHT (KM) 
9.6 
8.0 
6.4 
16 32 48 
WINOSPEED (m/sec) 
O WIND OBSERVATIONS 
x TOWER*X-CLOUDTI 
© TOWER Y-CLOUDI 
CHESTER W. NEWTON 
200 280 360 
63,000 
57,600 
52,500 
47,200 
42,000 
(14) LHOIGH 
36,800 
31,450 
26,200 
21,000 
DIRECTION 
(°F ROM N, 360° COMPASS) 
LEGEND 
V TOWER Q-CLOUDI 
O TOWER W-CLOUDL 
4 STREAMER- CLOUD ID 
Fic. 2—Horizontal movements of Cumulus towers near Anegada Island, 
compared with winds at San Juan, P.R. (120 mi WSW), 15h 00m GCT April 1, 
1953; from Malkus and Ronne [1954] 
of spring situations wherein the vertical shear is 
strong. In summer, these values would be on the 
average considerably smaller; on the other hand, 
the mechanical lifting required is often corre- 
spondingly less. The significance of momentum 
transfer lies in the fact that it augments the rela- 
tive motion due to outflow alone, and that the 
induced pressures are proportional to V2. Thus, 
if a relative motion of only 5 m/sec because of 
momentum transfer with modest vertical shear 
is added to a relative motion of 10 m/sec due to 
the outflow field of a thunderstorm, the kinetic 
energy of relative motion, and the potential for 
lifting, is still more than doubled. 
Effects of storm size—Equating the right-hand 
terms in (4) and noting that AP is proportional 
to V,2, it is seen that for steady motion of the 
cloud 
( zi) 
= 1 w D 
Oz 
Since 0Vr/dz = OVz/dz — OV./dz, for a given 
environment shear small 0V./dz is concomitant 
with large Ve at upper and lower cloud levels. 
Proportionality (5) then states that for a given 
intensity of vertical motion and of vertical shear, 
large relative motions and induced pressures are 
enhanced by large storm diameter. 
Thus propagation arising from shear is most 
favored when a rainstorm is of large size. This 
suggests a selective growth of large storms at the 
expense of small ones, which can be more readily 
sheared off without propagation of new cells on 
VR? 
