SNOW-CRYSTAL ANALYSIS AS INDIRECT AEROLOGY 
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Fra. 3—Diagram of temperature ranges derived from snow crystal analysis as basis of a temperature- 
height cross section, March 21, 1958 (Operation 27); thickness of layers are in meters 
the layers are taken as basis for the construction 
of a height cross section. As starting-point it is 
necessary to have a reference value, for which the 
relation temperature to altitude is taken from 
other facts of observation, for instance, from 
ground observations. The construction is then 
carried out in two parts (Fig. 2): 
(1) The thickness of temperature ranges in 
meters is entered in an equidistant scale of tem- 
perature for each observation time (above left). 
If several different types of crystal appear in one 
observation, as it is the rule in most cases, the 
diagram of the stratification can be further se- 
cured by comparisons of the single-layer thick- 
nesses determined from different snow particles. 
Thus, uncertainties of using average values for 
the rate of growth in relation to the state of satu- 
ration can be partly eliminated. 
(2) The temperature scale, derived from the 
analysis of the different crystals, is entered in the 
diagram with equidistant scale of altitude (above 
right). This operation is done in several steps, as 
explained in detail m Fig. 2, below. The state- 
ments about humidity are added at the right of 
the altitude-scale. 
These values obtained for all observations of one 
operation were put in a row (Fig. 3). A cross sec- 
tion for temperature and humidity constructed 
by the snow crystal analysis as derived according 
to the procedure described here is shown in Fig- 
ures 4 and 5. 
A comparison between the results from the 
snow-crystal analysis with the aerological state 
measured by soundings indicates (1) the aecord- 
ance in the existence of layers of defined qualities, 
especially the state of saturation combined with 
a defined temperature range and the structure 
of precipitation clouds (qualitative analysis), and 
(2) the quality of a quantitative analysis, espe- 
cially the question whether in spite of some nec- 
essary simplifications with respect to the use of 
mean values for the rate of growth the results are 
suitable for a fairly exact calculation of the thick- 
ness of defined layers. The results are as follows: 
The growth conditions of a crystal form, 
known from laboratory investigations, allow con- 
clusions regarding the temperature range and the 
state of saturation of the atmospheric layers in 
which the erystal originated. The qualitative 
crystal analy from consecutive observations 
during snowfall shows excellent agreement be- 
tween crystal types and synoptic development. 
Quantitative analysis for deriving the thickness 
of layers and for reconstruction of cross sections, 
based on rates of fall and rates of growth, as 
measured in laboratory experiments, show satis- 
fying agreement with the cross sections derived 
from aerological soundings for Jayers up to the 
—20° C level. Determination of the stratification 
for the upper atmospheric layers becomes more 
and more uncertain, as the rate of growth for 
columns and the upper temperature boundary 
for their origin seem to be doubtful. 
As the agreement of the reconstructed analysis- 
sections with the values from aerological measure- 
ments is best near the time of sounding, it can be 
5. 
