HORIZONTAL DISTRIBUTION OF SNOW CRYSTALS 
500 
600 
121 
500 
N 
° 
° 
600 
1 
1 
! 
1 
+ 
4 
\ 
ao 
So 
fo} 
700 
PRESSURE (mb) 
4 
900 
800 
PRESSURE (mb) 
1000 
900 
80 90 100 110 
HUMIDITY (%) 
-20 -10 ce) 
TEMPERATURE (°c) 
Fic. 5—Sounding curve at Sapporo, 09h 00m, January 20, 1959 
sounding data, the relation between the air tem- 
perature and the supersaturation with respect to 
ice was plotted on the Ta-s diagram [Nakaya, 
1954, p. 249] from the study of artificial snow 
crystals, as shown in Figure 6. The broken line in 
this figure indicates a line giving the saturated 
vapor pressure with respect to supercooled water. 
On the basis of the experimental results with ar- 
tificial snow crystals, it will be expected from 
Figure 6 that column (capped column), plate, 
dendritic, and scroll crystals would occur in such 
atmosphere aloft as shown in Figure 5. This ex- 
pectation agrees quite well with the results of the 
actual observations as shown in Figure 4. The 
plates observed in the southeast region are con- 
sidered to form in the warmer layer of Region II, 
since the plates formed in the cold layer of Region 
II would develop into dendritic crystals in the 
layer of Region I. On the other hand, the needles 
observed at 09h 30m in the east region cannot be 
explained from the sounding data, and so it will 
be local snowfall. 
As seen in Figure 4, it is noteworthy that the 
southeast region where plate crystals were ob- 
served did not change position during the period 
from 10h 30m to 12h 30m. This suggests that the 
meteorological condition suitable for the forma- 
tion of snow crystals continues for several hours 
during a snowfall. 
On January 30, the snowfall was due to the up- 
glide motion associated with the warm front. Sea- 
level, 850-mb, and 700-mb charts at 09h 00m 
are shown in Figure 7. As seen in the sea-level 
chart, the rain area reached the southern end of 
140 
rr) 
° 
Ss 
° 
SUPERSATURATION WITH RESPECT TO ICE (%) 
to) =-§ -10 -15 
TEMPERATURE (°c) 
=201 =25 
SAPPORO, O9OOJST, Jan.20,1959 
Fic. 6—T,-s diagram for the sounding at Sap- 
poro, 09h 00m, January 20, 1959; Region I, den- 
dritic; II, sector and plate; III, needle; IV, scroll 
or cup; V, irregular needle; VI, spatial plates; and 
VII, column 
Hokkaido, and snowfall occurred in the area 
northward from there. The amount of precipita- 
tion on this day was 28.5 mm at Sapporo, and 1.5 
mm at Iwamizawa. The difference in the amount 
of precipitation between these two places can be 
explained as follows. 
The horizontal distribution of snow crystals at 
