STRUCTURE OF SNOWFALL AND SNOW CRYSTAL DISTRIBUTION 143 
Sea 
of 
Okhotsk 
HOKKAIDO 
Sapporo 
oO 
A 
Mt Teine 
Pacific 
Ocean 
Fria. 1—Location of the observations 
4. Solid lines show isothermals and dashed 
lines represent relative humidity with respect 
to ice saturation. The thick solid line shows espe- 
cially the isothermal of —15°C around which 
snow crystals grow rapidly to form dendritic 
type. In general, moist air existed at the —15°C 
level on the 26th and night of 27th when light 
snow showers were observed at ground level. 
Early in the morning of 30th a cyclone passed 
through Hokkaido as shown in Figure 5 and 
warm moist air flowed into the observing area 
and brought heavy snowfall. This snowfall was 
on a large scale and the observation points were 
located to the lee of the mountain, so in this case 
the data obtained by rawinsonde sounding are 
considered to be reliable. Continuous snowfall 
was observed at Point 1000 during the period 
of the observation except on the 29th, but the 
moist-air occurrence at the Point 1000 was 
limited to a few short periods. This strange phe- 
nomenon is considered to be the result of con- 
densation of orographie ascending air, because 
the observed condensation level was always 
lower than the altitude of Point 1000 as shown 
on Figure 4. In addition to that, several small 
erystals of initial stage were almost always ob- 
served at the upper points. 
Therefore, the data obtained by the aspirated 
psychrometer were taken as the condition at al- 
titudes below 1000 m. As for levels higher than 
1500 m, the data obtained by rawinsonde were 
accepted as they were. The conditions at the in- 
termediate level between 1500 m and 1000 m 
were interpolated. The time cross seetion ob- 
tamed thus is represented in Figure 6 in which 
the layer lower than 3000 m is shown. The al- 
titudes of the five observation points are repre- 
sented by horizontal short thick lines on the or- 
dinate. The type of representative snow crystals 
observed at Point 1000, Point 500 and Point 100 
Fic. 2—Horizontal distribution of the observa- 
tion points 
Pt 1000 
10 
Pt.800 
° 
Pt.500 
fo} 
Pt.300 
° 
=e 2 3 4 
HORIZONTAL DISTANCE IN KM 
oe 
° 
Fic. 3—Vertical distribution of the observation 
points 
