HORIZONTAL DISTRIBUTION OF SNOW CRYSTALS 127 
ern half of Japan. The amount of precipitation 
was 0.0 mm at Sapporo (Sta. 2), and 2.4 mm at 
Iwamizawa (Sta. 13). 
The horizontal distribution of snow crystals at 
09h 30m, 10h 30m, 11h 30m, and 12h 30m is 
shown in Figure 16. The characteristic of this 
snowfall was that plate and column (capped col- 
umn) crystals were observed widely in the ob- 
servation area. 
The sounding curve at 09h 00m is shown in 
Figure 17, and Ta-s diagram for these sounding 
data is shown in Figure 18. It will be expected 
from Figure 18 that spatial plate, plate, and col- 
umn crystals would be the main shapes in this 
snowfall. Besides, dendritic erystals may form in 
Region I, but will not be so predominant, since 
the supersaturation with respect to ice was 110%, 
that is, nearly the critical value for transition 
from a plate to a dendritic form. These expecta- 
tions agree with the results of observations, as 
seen in Figure 16. The snow-crystal form recorded 
as irregular crystals by observers is considered to 
be spatial plate. From Figure 18, it may be con- 
sidered that column crystals formed in the 
warmer layer of Region VII, but that was not the 
case. Since the capped column was observed at 
some observation points, the column should form 
in a layer higher than a layer suitable for den- 
dritic or plate, that is, in a colder layer of Re- 
gion VII. However, no colder layer responsible 
for the generation of crystals of Region VII was 
observed by the sounding, as seen in Figure 18. 
This discrepancy must have been due to the hori- 
zontal difference of supersaturation in the upper 
layer. 
In this snowfall, the areas where the same 
shape of snow crystal was observed could not be 
500 500 
600 600 
z @ 
= 700 700 ~ 
¥ ¥ 
= =] 
2) w 
u w 
w w 
& 800 800 & 
a a 
900 900 
1000 1000 
ew 
80 90 100 110 12 -20 -10 fo) 
HUMIDITY (%) TEMPERATURE (°c) 
Fic. 17—Sounding curve at Sapporo, 09h 00m, 
February 16, 1959 
140 
130 
120 
SUPERSATURATION WITH RESPECT TO ICE (%) 
100 
95: 
25 
= 5) =O p15) 1-20 
TEMPERATURE (°c) 
Fre. 1S—T,-s diagram for the sounding at 
Sapporo, 09h 00m, February 16, 1959 
decided, since the mixing of snow crystals was ob- 
served at many stations. 
Concluding remarks—Simultaneous observa- 
tions of the shape of snow erystals were carried 
out at 14 points in an area of about 5200 km* in 
the Ishikari Plain, Hokkaido. Though this inves- 
tigation was a preliminary one, it was found that 
areas where the same shape of snow crystals are 
to be observed can be detected by observations 
in an area as wide as in this case. However, a 
wider area of observation will be necessary for 
fully understanding the snowfall caused by the 
large-scale motion associated with frontal zones. 
Therefore, further observations in the winter of 
1959-1960 will be carried out over a wider area, 
and by the use of more precise methods, such as 
plastic replica or shadow photograph. 
In conclusion, the authors express their hearty 
thanks to C. Magono for his criticism through 
this work. The authors are much indebted to A. 
Ichikawa for his kind assistance in carrying out 
this work, and to the Sapporo Meteorological 
Observatory, to the Iwamizawa Weather Station 
and to the Hokkaido Scientific Education Society 
for carrying out the observations of snow erys- 
tals. 
