98 WALTER HITSCHFELD 
pictures) are illustrated by dashed lines. Con- 
sider the line joining the 35 and 30 kft points 
in Figure 5b. Its southern extremity would be 
formed by particles of fall speed v = 1 ft sec”, 
which would have traveled some 128 mi from 
their origin at 35 kft, requiring 5000 see (about 
84 min) to do so. Particles of twice that fall 
speed would reach the 30 kft level at the point 
marked v = 2, about 64 mi from their origin at 
35 kft. The northern end of this plume would be 
formed by particles of increasingly higher fall 
speeds. The times required by these particles to 
reach their positions in the plumes also depend 
on their fall speeds, and three values are indi- 
cated in the diagram. The plume appearing at a 
height of 25 kft, and also made up of particles 
originating in the storm at 35 kft is similarly 
represented by the dashed line joining the 35 
and 25 kft points. If particles from the storm 
enter the wind field at 30 kft their trail would 
be as shown in Figure 5c (solid lines). At a height 
of 25 kft, such particles would give rise to a 
plume, oriented almost exactly north-south, as 
shown by the dashed line. 
Comparison with observations: particle fall 
speeds—Some of the plume observations are il- 
lustrated in the CAPPI photographs of Figure 2, 
and again in the schematic sketches of Figures 
40 
= \ Sa 
= Ne 1 
l= Sos 
= 
£3: 
a 
as 
oe EST 
Co) —— er 
40 
a 
oo 
T 
fe) == 1 — 
4ob 
eS me > ~, 
a 
OS. 1550 
tf ve = = 
r 
\ 
ie) 
fo) 20 MILES 40 60 
Fia. 6—Vertical sections along bearing 340° 
through Storm 1, showing the gradual decay of 
the core and development of the plume during one 
hour; plumes shown in dashed outline (two-fold 
vertical exaggeration) 
6, 7, and 8. Figures 6 and 7 show vertical sec- 
tions through Storms 1 and 2 and their plumes. 
The directions of these sections were chosen 
along the 340°-160° plane to coincide approxi- 
mately with the longest extent of the plumes. In 
Figure 7 the progression of the pluming storm 
through the field of view of the radar is also indi- 
cated by horizontal sections through the radar 
patterns at a height of 5 kft. (Where these hori- 
zontal sections are dashed, they were taken 
through the plume at 10 kft.) Figure 8 shows 
the development of Plume 3 as it appeared at 
25 kit. 
These observations are readily interpreted in 
terms of the preceding analysis. The predomi- 
nant direction of the plumes in Figure 8 is 835°— 
155°, and so agrees exactly with that of the 
derived pattern shown in Figure 4, for particles 
originating at 35 kft. That this level is the prin- 
cipal source of particles is also borne out by an 
analysis of the rate of southward elongation of 
the plumes prior to 17hO8m. This rate can be 
shown to be a function only of the height inter- 
val through which the particles are falling and 
the wind pattern they encounter en route, and 
is independent of particle speed. The rate ob- 
served here, which is about one mile min”, fits 
35 kft as an origin. (For an origin at 30 kft the 
rate would have been only 0.44 mile min™.) The 
apparent lengths of the plumes cannot be deter- 
mined with great accuracy, since the line of de- 
marcation of storm core and plume cannot easily 
be drawn. But at 16h57m, the plume at 25 kft 
is about 32 mi long, which by direct comparison 
with the plume derived in Figure 5b (length 
160 mi for v = 1 ft sec’) would mean that the 
particles in the southern tip are falling at about 
5 ft see*. At 17hOSm, the plume is about 37 mi 
long and this indicates that particles falling as 
slowly as 4.3 ft sec* have now reached the 25 kft 
level. By 17h20m the plume lengthened to its 
maximum dimension of 45 mi; minimum fall 
speeds are therefore 3.6 ft see*. One can check 
the times of departure of these particles from 
the 35-kft level, and find that they all agree 
reasonably well, being between 16h15m and 
16h30m. The first sign of a plume at that level 
appeared on the radar records at about 16h27m. 
The radar record of 17h47m is the last one 
showing an intense core at 35 kft. This probably 
was therefore the last instant at which particles 
entered the free atmosphere at that level. From 
this time on, the particles already in the trail 
continued to fall, but the northern end of the 
