Snow Crystal Analysis as a Method of Indirect Aerology 
JOHANNES GRUNOW 
Deutscher Wetterdienst, Meteorological Observatory Hohenpeissenberg, Germany 
Abstract—Observations of form and size of snow crystals, whose conditions of growth 
are widely known from laboratory investigations, were compared with the synoptic 
situation. The qualitative analysis obtained by a general survey of all forms appearing 
at the same time imparts an insight to the structure of the atmospheric layers in their 
temporal and spatial succession. A quantitative analysis is developed to derive the 
thickness of layers and to reconstruct cross sections of temperature and state of satura- 
tion, based on rates of fall and rates of growth as known from laboratory investigations. 
The results show satisfying agreement with the cross sections derived from aerological 
soundings for layers up to —20°C. From measurement of numerous shadow photos, it 
was possible to derive frequency-sections and spectra of the distribution of sizes for 
some crystal forms that permit statements concerning the structure of the precipitating 
cloud system. From evaluation of water droplets attached to snow crystals, spectra of 
the diameters of droplets for different air masses were derived. Even simple observa- 
tions of snow crystals from different altitudes made by the visual method show char- 
acteristic differences of form and size of the crystals. Thus the suitability of the snow 
crystals as aerological sonde is confirmed by many single manipulations. 
Introduction—During the past decades the 
study of the ice-phase in the atmosphere has 
yielded important insights in fields of cloud phys- 
ics and in the formation and release of precipita- 
tion. With this knowledge, investigations of snow 
crystals on the ground, particularly on mountain 
stations, have proven to be useful as can be seen 
from the work of Weickmann [1957ab] on Mt. 
Hohenpeissenberg, Germany (located in the 
northern foreland of the Alps) and Kuettner and 
others [1956, 1958] on Mt. Washington, N. H. 
The form and size of snow crystals, whose condi- 
tions of growth have been widely known from nu- 
merous laboratory investigations, allow conclu- 
sions concerning the structure of the precipitation 
cloud system and upon the temperature and hu- 
midity within the upper air layers. In order to 
check these results under different climatie con- 
ditions and to complement the observations in the 
upper air layers with aerological measuring de- 
vices during the IGY, consecutive records of snow 
crystals by photographic methods, as shadow- 
macro- and microphotography, and by replica 
technique, were made on Mt. Hohenpeissenberg 
during the winter of 1957-1958 [Grunow and 
Huefner, 1959]. The conclusions drawn from the 
form analysis of snow crystals with respect to the 
state of the upper air layers were compared with 
the synoptic situation as determined by the data 
obtained by the usual sounding procedure. 
130 
Qualitative analysis—The manifold forms of 
snow crystals with their innumerable variants 
depend upon the atmospheric conditions, particu- 
larly upon temperature and state of saturation, 
that prevailed during their formation and along 
the path of fall. The ranges of temperature and 
humidity are demonstrated in the diagrams of 
Nakaya [1954], Aufm Kampe and others [1951], 
and Weickmann [1957a]. Nakaya chooses as or- 
dinate units of the relative humidity as a measure 
of the supersaturation with respect to ice, while 
Weickmann uses the vapor-pressure difference 
between water and ice saturation. Recent in- 
vestigations by Kobayashi [1957, 1958] on the 
habit of snow crystals artificially produced at low 
pressures show a relationship of the shape of 
crystals to the ambient vapor density. There- 
with the necessary conditions for the growth of 
each crystal type are known, namely, the ranges 
of temperature and the variation of humidity 
(state of supersaturation and ambient vapor 
pressure). It is possible to deduce from the suc- 
cessively grown parts of a snow particle that has 
fallen through the atmosphere, the conditions of 
the air layers during its passage. This statement 
about the structure of the atmospheric layers in 
their temporal and spatial succession we define 
as qualitative analysis. 
Such a qualitative analysis requires a general 
survey of all forms appearing at the same time, 
and their arrangement according to a detailed 
