GROWTH AND STRUCTURE OF GRAUPEL AND HAILSTONES 319 
Fic. 2—Thin section through hailstone 57.15 under translucent light; real length of the figure, 3.0 
em 
a result the particle developed different aero- 
dynamic behavior and this led to the establish- 
ment of a new center of symmetry. 
It may be remarked here that growth in one 
place may be the result of two different phases, 
the one ‘overlaying’ the other. This oceurs when 
a primary ice formation produces a loose ice 
framework, air capillaries of which become filled 
with liquid water at a later stage; this then 
freezes either entirely or in part. 
It is this ‘overlaying’ process which gives us a 
generally better picture of the original center 
than of the later phases, contrary to the views 
of Dessens [1959]. As an example, Figure 1 may 
again be referred to. We know that normally a 
graupel acts as the basic particle of a hailstone. 
Hailstone 57.15 indicates by the conical sym- 
metry of the initial particle that the graupel 
was also conical. Since, however, the shape of 
this central zone is ellipsoidal, this means that 
the graupel has absorbed slow-freezing water 
into its cohesive system of caverns. This has 
brought about its transformation into a small 
hail particle with the surface tension of the wet 
surface leading to a roundish shape. Such over- 
layings cannot be so well recognized in later 
phases. 
ICING NUCLEUS 
ICE CRYSTAL 
rapid freezing 
Sublimation 
Increase in volume 
Ww 
x= o 
c : 
5 GRAUPEL is a 
i FS (soft hail) = eo 
a wo fe 
w ° c = 
o|s & ° 
WW - slow freezing c S 
a | ° = 
> o 
r|s ain 
ry i = 
5 Vl gz 
< SMALL HAIL t+ 
(= 
> 
E 
slow or rapid freezing < 
eo 
“” 
o 
Y 2 
HAILSTONE 2 
——— ———————— 
Fic. 83—Characteristics of the growth of a hail- 
stone 
GrowTH FROM Icr-FormMInc NucLEus 
To HaILsToNE 
On the basis of observations made between 
1953 and 1959 on graupel and hailstones the 
