Horizontal Distribution of Snow Crystals during the Snowfall 
Uxicutro NAkAyA AND Ketst Hicucut 
Faculty of Science, Hokkaido University, Sapporo, Japan 
Abstract—Simultaneous observations of the shape of snow crystals were carried out 
at 14 points in an area of about 5200 km* in the Ishikari Plain, Hokkaido, in the period 
from January 20 to February 28, 1959. The horizontal distribution of snow crystals and 
its time sequence on four days; namely, January 20, January 30, February 10, and 
February 16 are analyzed in detail. From these results, it was confirmed that a depend- 
ence of shape of natural snow crystals on temperature in the upper atmosphere was in 
reasonable agreement with that of artificial snow crystals. On the other hand, it was 
found that the area where the same shape of snow crystals was observed might have 
some relation to the isothermal lines in the upper atmosphere. 
Introduction—In the recent researches on nat- 
ural snow crystals, the relationship between the 
shape of snow crystals and meteorological condi- 
tions was studied by many workers. It was con- 
firmed by Gold and Power [1954], Murai [1956], 
and Kuettner and Boucher [1958] that a de- 
pendence of shape of snow crystals on tempera- 
ture in the upper atmosphere was in reasonable 
agreement with that found in the laboratory by 
Nakaya [1954, p. 249]. On the other hand, Weick- 
mann [1957, pp. 239-241] observed the time se- 
quence of snow-crystal forms during continuous 
precipitation, and suggested that the snow crys- 
tals could be used as an aerological sonde. How- 
ever, there have been no studies on the horizontal 
distribution of snow crystals during a snowfall. 
The influence of the area where the same shape 
snow crystals are observed will be one of the im- 
portant problems in the research on precipita- 
tion systems. From this standpoint, simultane- 
ous observations of snow crystals were carried out 
at 14 points in an area of about 5200 km’. The 
results from these observations will be described 
in this paper. 
Observational procedures—Simultaneous ob- 
servations of the shape of snow crystals were car- 
ried out at 14 points in an area of about 5200 km? 
in the Ishikari Plain, Hokkaido, in January and 
February, 1959. A map of Hokkaido is shown in 
Figure 1, in which the observation area is indi- 
cated by a square surrounding Sapporo; the lo- 
cation of Hokkaido is shown in the upper left 
corner. The topographical map of the observation 
area is shown in Figure 2, where the observation 
points or stations are numbered 1, 2, ete. Station 
2 is in Sapporo, where aerological data are ob- 
tained using Rawinsonde by the Sapporo Me- 
teorological Observatory at O9h OOm and 21th 
00m JST (Japan Standard Time) every day. 
The observation of snow crystals was requested 
of the teachers of senior or junior high schools at 
stations noted above. The observations at Station 
2 were made by the Sapporo Meteorological Ob- 
servatory, and those at Station 13 by the Iwami- 
zawa Weather Station. Since the observers had 
no experience in the observation of snow crystals, 
such methods as the use of microscope or replica 
or shadow photograph could not be employed. 
Therefore, observations were made with the 
naked eye or a magnifying glass. 
The shape of snow crystals was recorded by 
graphic symbols of the practical classification of 
Nakaya [1951, p. 311], in which the snow crystals 
were classified into the following eight classes: 
(1) plates O, (2) stellar crystals ¥, (3) columns 
O, (4) needles «, (5) spatial dendrites ©, (6) 
capped colums -, (7) irregular ‘crystals x), and 
(8) graupel X . 
The period of observation was 40 days from 
January 20 to February 28, 1959. The time of ob- 
servations was at 09h 30m, 10h 30m, 11h 30m, 
and 12h 30m, JST on each day that snowfall oe- 
curred. Since the aerological observation by Ra- 
winsonde at Sapporo is carried out at 09h 00m 
as noted above, such times of observation are 
reasonable for studying the relation between the 
shape of snow crystals and meteorological condi- 
tions. 
Besides the shape of snow crystals, it was re- 
quested that observers record the qualitative in- 
tensity of the snowfall and the occurrence of snow 
flakes. 
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