DISCUSSION 
1957, on Mount Washington on the contract 
sponsored by Dr. Weickmann, we found as did 
Dr. Grunow and Dr. Nakaya, a very good corre- 
lation between the synoptic situation and the ice 
crystals. We made three kinds of analyses: (1) 
radar, (2) synoptic, and (3) ice-crystal analysis; 
the last I did myself. It is quite surprising how 
well one can determine the conditions aloft. 
Now, I would like to offer a word of caution. 
The main problem arises not from the mixture 
of ice crystals, but from the Nakaya diagram in 
which there is a duality of identical forms coming 
out on both sides of the diagram. In many oc- 
casions, for example, we have the occasion of hol- 
low needles or long columns which one does not 
know exactly where to place. The same thing hap- 
pens with plates; only with dendrites, there is 
no problem. 
Dr. Horace R. Byers—I notice in Dr. Nakaya’s 
data that the clouds seemed to be entirely below 
the 800 millibar surface; therefore, there are not 
great multiple layers involved. This is true also of 
the systems which produce snow on the exposed 
sides of the Great Lakes; therefore, you do not 
have there this multiplicity of crystal types. 
Augmenting what Dr. Weickmann said in re- 
gard to even those clouds which are very thick, 
it is my experience in observing them in Chicago 
or elsewhere, without lake or other special in- 
fluences, that one almost never gets a mixture of 
types. It is usually one type. The type may 
change during the course of a storm, but at any 
given instant there will be usually just one type. 
Dr. R. List—Regarding the comment of Mr. 
Aldaz, I can show you a dendrite that was found 
in a cloud with temperatures above about —4°C. 
It appears to have been grown at —15°C, but we 
know it was grown at temperatures higher than 
—4°C. 
Mr. Aldaz—How do you know? 
129 
Dr. List—Our institute is on the top of a moun- 
tain, and we can see the top of the clouds very 
well. 
Dr. C. L. Hosler—Two winters of observations 
of snow and activity in central Pennsylvania sel- 
dom got mixtures, and snowflakes were about 
80% dendrites. We did not observe mixtures at 
all. 
Dr. C. J. Grunow—In the cases of February 
10 and 16, the behavior of columns is in con- 
tradiction with the results found in your labo- 
ratory investigations. We found the same: the 
conditions of growth for columns must be some- 
what other than defined in the Nakaya diagram. 
Also the observations of Dr. Weickmann in natu- 
ral Cirrus clouds suggest the beginning of growth 
for columns at a lower temperature. Considering 
results of Kobayashi, it follows that not only the 
temperature and the state of saturation but also 
the ambient vapor density is an essential factor 
of growth. In the Kobayashi-diagram the column 
dominates in a range of little ambient vapor den- 
sity independently of any temperature ranges. 
Can the named doubtful cases in the behavior 
of columns be explained by this effect ? 
Dr. Nakaya—I admit that my diagram is now 
almost 20 years old and it must be revised by the 
advanced technique of experimentation in this 
field. Mr. Kobayashi is now working on this prob- 
lem in the Low Temperature Institute of our 
University. The problem exists not only in the 
point of the ambient conditions but also in the 
point of the definition or classification of the type 
of crystals. The columns are the most embarrass- 
ing type. Short needle, sheath type, column with 
thinner wall and the ordinary column belong to 
the same category; growing more in the direction 
of principal axis and less in the direction perpen- 
dicular to it. More detailed studies must be car- 
ried out for distinguishing one type of crystal 
from the other belonging to this same category. 
