SNOW AND EXPERIMENTAL METEOROLOGY 
and irregular crystals (the latter probably formed on 
fragmentation nuclei) constitute the major portion of 
the snow reaching the ground. It is this chain reaction 
mechanism which must be responsible for most exten- 
sive snowstorms not seeded by high-level clouds. 
5. Electrification Ice Nuclet. That some type of elec- 
trification may be an important producer of ice nuclei 
is suggested by laboratory experiments and field obser- 
vation. If a field of several hundred volts per centimeter 
is established in a supercooled cloud, dendritic treelike 
growths may form if some ice crystals are present. These 
treelike forms seem to grow from a combination of 
crystals and supercooled cloud droplets. Subsequently 
227 
Figure 12 illustrates the type of atmospheric electricity 
observed in snowstorms. 
Electrical Properties of Snow 
It is very likely that the chain reaction mechanisms 
suggested by the operation of fragmentation processes 
at temperatures from —12C to —20C and the interest- 
ing effects observed in electric fields are complementary 
mechanisms. Since snow crystals reaching the ground 
are often electrically charged, it seems obvious that 
they are indicators of mechanisms operating in the 
atmosphere where they were formed. The electrification 
may be a causative agent or an end result. The highest 
Fig. 11—Types of snow erystals which are probably important in the formation of fragmentation nuclei. 
they break and form many ice fragments, each of which 
becomes a potential ice crystal. 
This effect has never been observed unless ice crystals 
were already present, and it may be associated with the 
Workman-Reynolds effect [42]. Although it has so far 
been impossible in the General Electric Research 
Laboratory to show any freezing effect or production 
of nuclei using either a-c or d-c fields up to 1 kv em 
in a supercooled cloud, a temporary coexistence of 
cloud droplets and ice crystals shows electrification 
phenomena which may be of great importance. These’ 
effects may be of primary importance in the establish- 
ment of the chain reaction which seems to be necessary 
to produce the many crystals required to form an ex- 
tensive snowstorm. Certainly high fields are present in 
many snowstorms [22], particularly in those charac- 
terized by convective activity and supercooled clouds. 
amounts of atmospheric electricity observed occur at 
temperatures not far below freezing and with broken 
stellars, needles, spatial dendrites, and sleet particles, 
all of which could be associated with fragmentation and 
electrification processes. Typical air-to-ground currents 
during a snowstorm are shown in Fig. 12. 
The fact that the fragmentation of snow crystals 
causes a large increase in the charging potential of 
snow crystals shows the close interrelation which must 
exist between these two effects [22]. Further studies in 
this field should produce important results. 
Factors Controlling the Life Cycle of Supercooled 
Clouds 
The icing of aircraft, the formation of hail and 
graupel, and the electrical phenomena of thunderstorms 
are typical products of supercooled clouds. The growth, 
