HORIZONTAL DISTRIBUTION OF SNOW CRYSTALS 
was SW at the altitude from 3.5 to 4.0 km where 
dendritic crystals formed, the dendritic crystals 
are considered to have drifted to the NE by 
the wind aloft. On account of such difference of 
the direction of drifting, it will be reasonable that 
the area of stellar crystals existed to the north- 
east of the area of needles. 
On February 10, the snowfall was due to the 
passage of the cold front. Sea-level and 700-mb 
charts at 09h 00m are shown in Figure 11. The 
snowfall area was the northern part of the Japan 
Sea coast of Japan. The amount of precipitation 
was 15.5 mm at Sapporo, and 1.7 mm at Iwami- 
zawa. 
The horizontal distribution of snow erystals at 
09h 30m, 10h 380m, 11h 30m, and 12h 30m is 
shown in Figure 12. As seen in this, the character- 
istic of this snowfall was the transition from the 
state of predominance of stellar crystals at O9h 
80m to that of needles at 12h 30m. 
The sounding curve at Sapporo at 09h 00m is 
shown in Figure 13, and Ta-s diagram for those 
sounding data 1s shown in Figure 14. It will be 
expected from Figure 14 that spatial plate (spa- 
tial dendrites), plate, dendritic, scroll, and needle 
crystals would occur in such atmosphere. This 
expectation agrees with the actual observation re- 
sults shown in Figure 12, excepting the occurrence 
of column crystals. The layer suitable for forma- 
tion of dendritic crystals was from the altitude 
of 2.5 to 2.8 km; this was in concordance with 
surface observation of clouds, reporting that there 
was Altostratus [Kuettner and Boucher, 1958] at 
3 km at 09h 00m JST. The layer suitable for for- 
mation of needles was from the altitude of 0.9 
to 1.3 km, which is im concordance with the data 
of surface observation, reporting that there was 
500 500 
600 O = —j 600 
E é 
~ 700 700 
w w 
§ 3 
n 2) 
7) wn 
& 0 & 
ee 800 80) er 
900 900 
1000 1000 
80 90 100 110 120 
HUMIDITY (%) 
-20 -10 te) 
TEMPERATURE (%) 
Fic. 13—Sounding curve at Sapporo, 09h 00m, 
February 10, 1959 
140 
130 
120 
110 
SUPERSATURATION WITH RESPECT TO ICE (%) 
100 
95 
=1'5 
TEMPERATURE (°c) 
= 5 =O =20) =25 
Fia. 14—T,-s diagram for the sounding at Sap- 
poro, 09h 00m, February 10, 1959 
Fractonimbus at 0.9 km in the period from 09h 
00m to 12h 00m. 
As indicated by N in Figure 12, the area where 
needles were observed expanded in the period 
from 09h 80m to 12h 50m. At 09h 30m, the stel- 
lar crystals were predominant, while needles were 
observed only at Station 2 (Sapporo). At 10h 
80m, the area of needles moved westward, needle 
crystals being observed at Stations 8 and 13. At 
11h 30m, the area of needles expanded in the 
longitudinal direction, while snowfall stopped in 
the areas other than this area. At 12h 30m, the 
area of needles expanded more than that at 11h 
30m. The reason for this transition cannot yet be 
explained. It must be noted, however, that the ex- 
panding direction of the needle area was parallel 
to the direction of the isothermal line in the upper 
ar, as seen in the right-hand chart in Figure 11. 
This result was the same as that of January 30, 
and is very interesting. 
On February 16, the snowfall was due to the 
passage of the trough in the upper atmosphere. 
Sea-level and 700-mb charts at O9h 00m are 
shown in Figure 15. The snowfall area was in 
Hokkaido, and the rain area was over the north- 
