HORIZONTAL DISTRIBUTION OF SNOW CRYSTALS 
123 
500 500 
2 ee Ny 
ae ih X 
ay N 
600} <9 a v a 600 
i a 
m a j \ zs 
a \ 
t . — 
£ 700 a A Ss - 700 ~ 
Ww 
ie i NS ie 
= i Ne \ im 
w ' bX \, wn 
! : N my 
& 800 ' <— | 800 & 
a 1 XN r 
5 \ 
t | x 
900 Sk | : 900 
o- H | 
bse, 
1000 : 1000 
go 90 100 110 120 -20 -10 ) 
HUMIDITY (%) 
TEMPERATURE (°c) 
Fre. 9—Sounding curve at Sapporo, 09h 00m, January 30, 1959 
09h 30m, 10h 30m, 11h 30m, and 12h 50m was as 
shown in Figure 8. As seen in these figures, the 
peculiar characteristic of this snowfall was that 
needle crystals were observed in the southern 
half of the observation area, indicated by N. On 
the other hand, snowfall was not observed in the 
northern half of the observation area, except that 
plates were observed at 09h 30m and 10h 30m at 
some stations. 
The sounding curve at 09h 00m is shown in 
Figure 9, and Ta-s diagram for the sounding data 
is shown in Figure 10. It will be expected from 
Figure 10 that column (capped column), plate, 
dendritic, scroll, and needle crystals would occur 
in such atmosphere aloft as shown in Figure 9. 
As seen in Figure 8, this expectation agrees with 
the result of observation in the southern half of 
the observation area. The predominance of the 
occurrence of needles can be explained from the 
existence of the deep layer warmer than —10°C 
where needles form, as seen in Figure 9. 
As indicated by N and § in Figure §, the area 
where needle and stellar crystals were observed 
is limited by an east-west line. This direction was 
not parallel to the direction of wind aloft, but 
parallel to the direction of the isothermal line in 
the upper air, as seen by the middle and right- 
hand charts of Figure 7. This seems to be a sug- 
gestive observation for further research on the 
system of snowfall. The reason why the snowfall 
in this case was limited to the southern half of 
the observation area cannot be explained now, 
but will be investigated in the further analysis. 
At 09h 30m and 12h 30m, the area where stel- 
140 
SUPERSATURATION WITH RESPECT TO ICE (%) 
-5 -10 =1/5 -20 =25) 
TEMPERATURE (°C) 
Fic. 10—T,-s diagram for the sounding at Sap- 
poro, 09h 00m, January 30, 1959 
lar crystals were observed most frequently existed 
northeast of the area where needle crystals were 
predominant, as seen on the 09h 30m and 12h 
30m charts of Figure 8. This situation may be ex- 
plained by the drifting of snow erystals by wind 
aloft. As seen in the left part of Figure 9, the 
direction of wind aloft was SE and SSE at the 
altitude from 1.0 to 2.5 km, where needles formed. 
Therefore, the needles are considered to have 
drifted to the NNW by the wind aloft. On the 
other hand, since the direction of wind aloft 
