DISCUSSION 
Discussion 
Dr. H. Dessens—Was this storm with or with- 
out hail? 
Dr. W. Hitschfeld—There was hail in the 
plume, but very little. Hail was observed on the 
ground, but it was small and insignificant. We do 
not get much hail in Montreal. 
Dr. E. Kessler—Do you think that the evapo- 
ration of parts of the plume, and therefore the 
cooling of the top of the layer immediately below 
and its destabilization might contribute to the 
observed structure in the base of the plume? 
Dr. Hitschfeld—Yes, indeed. In this connec- 
tion I might mention again the work of Imai in 
Japan, who had RHI pictures showing some 
mamatus at anvil base. 
Mr. C. E. Anderson—Your paper bears out 
some ideas that I have. I feel that by watching 
how a cloud dies, one can learn a lot about the dy- 
namics of the cloud, because the manner in which 
it dies gives a clue as to how it has lived. You 
showed that you had a continuous production of 
particles at 35,000 ft which sent down streamers 
with the wind for an hour. This we have noted 
also in anvils in the southwest, and we could only 
interpret this to mean there was some type of 
continuous updraft within the cloud producing 
the plume. Sometimes we noted new cloud devel- 
opment in the plume away from the core of the 
main cloud as it moved down stream a bit. 
Dr. Hitschfeld—At what height are your 
plumes? 
Mr. Anderson—These would vary, sometimes 
25,000 ft, but usually higher. 
Dr. Hitschfeld—This, I think, is vital because 
as I am showing elsewhere (McGill University 
Report MW, July 29, 1959) if the plume is warm 
enough to be supercooled water, there is no 
reason why there should not be new generation 
of precipitation im it. But in the plumes I was 
emphasizing here, I know this was not the case 
because the temperatures were much, much too 
low. 
Dr. H. Weickmann—Do you have any indica- 
tions of differences of lifetimes between storms 
with strong wind shear and storms with little 
wind shear? 
Dr. Hitschfeld—No. 
Dr. Weickmann—I am asking because by car- 
rying away the anvil the high-level jet may alter 
the life history of the storm as determined by 
cloud physical processes. From the Byers- 
Braham thunderstorm model we know that the 
developing state is followed by the mature state 
and this by the dissipating state. The mature 
state is characterized by updrafts prevailing 
throughout the cloud, whereas the dissipating 
state is characterized by downdrafts throughout 
the cloud and by an increasing predominance of 
the ice phase in the cloud. Byers and Braham 
have pointed out a mechanism by which down- 
drafts form in the upper parts of the cloud. These 
downdrafts will counteract the bouyancy of the 
rising cloud air and may thus mark the beginning 
of the dissipating state. If these downdrafts are 
displaced away from the original cloud by the ac- 
tion of a strong wind shear, they may not initiate 
the dissipating state and the cloud may stay alive 
in the mature state. 
Dr. Hitschfeld—In spite of the fact that the 
system is being deprived of water all the time? 
Dr. Weickmann—Yes, because it is only de- 
prived of water which has spent already its en- 
ergy for the cloud, whereas new moisture can 
continuously be fed in at the base, depending on 
the depth of the moist layer, inflow velocity, 
and migration velocity of the storm. 
Mr. Jerome Namias—I would like to ask a 
question of you or the audience which has puz- 
zled some of us for 20 years. Over the southern 
plains of the United States in the summer we have 
a condition in which an upper-level anti-cyclone 
develops and moisture flows around it in the form 
of great moist tongues. In the Great Lakes area 
rain falls from the warm front, as this moisture 
is forced over colder air, and much thunderstorm 
activity takes place. In many of these cases there 
is a very strong vertical wind shear so that the 
southwest surface flow from the Bermuda high 
is overrun by northerly components. As a re- 
sult, these thunderstorms move southward in 
clusters. In earlier studies I showed (Bul. Amer. 
Met. Soc., 19, 1-14, 1938) that the moisture 
pumped up by these thunderstorms is carried 
by the wind and in some way sets off chains of 
thunderstorms that move in the fashion indi- 
cated. In the 1930’s we tried to explain this on 
the basis of radiational cooling from the cloud 
tops or perhaps lack of entrainment. Have you 
some new explanation to suggest; namely, a 
