STRUCTURE OF 
SNOWFALL AND SNOW CRYSTAL 
DISTRIBUTION 147 
2000 
S 
Lo) 
IN M 
ALTITUDE 
$00 
-10 ~5 (°C) 
TEMPERATURE | 
80 90 100 (%) 
REL. HUM.(ICE SAT.) | 
Fia. 7—Growth of snowflakes 21h 30m—21h 50m, Jan. 27, 1959 
Time Section B: On the 28th, snow crystals 
of dendritic type continued to fall. It cleared off 
about 15h00m but the crystals continued to 
fall although it was a light fall. The snow crys- 
tals were of very beautiful plane dendrites form. 
The vertical distribution of air temperature and 
humidity at 21h00m is shown in Figure 8. There 
existed a thick layer of —15°C near Point 1000 
actually. It is notable that the air was not satu- 
rated and there were no clouds nearby; however 
perfect snow crystals fell and grew as shown in 
the left-hand part of the figure. The size dis- 
tribution is shown in Figure 9 starting with a 
erystal diameter of 0.5 mm. It is noted that the 
mean diameter of the snow crystals observed at 
Point 500 was markedly larger than that at 
Point 1000. The mean diameter of snow crystals 
at Point 100 is about the same as that at Point 
500, resulting from the fact that the air layer 
between Point 500 and Point 100 was dry. The 
tips of the branches of snow crystals observed 
at Point 100 were, to some extent, changed to 
sector form. 
The observational fact that dendritic snow 
erystals grew in air not saturated with respect 
to ice may be thought to be strange. Concerning 
the fact, the error of the humidity measurement 
should be considered first. The error of the psy- 
chrometer was +0.05°C. The error margin cor- 
responds to about +2% at —15°C, therefore the 
air whose humidity was lower than around 95% 
as seen in Figure 8 should be considered to be 
not saturated to ice. At least it is sure that the 
air was not saturated with respect to water. 
Generally it is considered from laboratory ex- 
periments that dendritic snow crystals grow in 
