332 
The Krakatoa eruption and the subsequent phe- 
nomena show that three-dimensional diffusion problems 
in the upper atmosphere cannot be solved without con- 
sidering the average horizontal and vertical motions 
and the pertinent steady or unsteady deformation fields 
of representative motion. 
PROSPECTS FOR FUTURE WORK 
The present-day inadequacies of the field require ex- 
perimental as well as theoretical investigations. 
More plentiful and improved observations of the 
composition and the geophysical conditions of the upper 
atmosphere with the aid of high-altitude balloons and 
rockets will stimulate considerably the interest in dif- 
fusion problems. To be certain of the representativeness 
of the data, it is imperative that upper-level soundings 
should be distributed more uniformly than before with 
regard to season and geographic latitude. 
The deficiencies of our knowledge are fairly well illus- 
trated by Fig. 2. The purpose of this graph was to 
demonstrate how an assumed D(z)-function affects the 
height variation of gas concentration in the strato- 
sphere. Only when D(z) can be verified more soundly 
than by arbitrary assumptions can the composition of 
the stratosphere be computed. 
The most promising method of direct attack requires 
chemical analyses of the air at levels above 15 km, 
especially from the layers of presumably small turbu- 
lence at 20-30 and 80-100 km approximately. Because 
of certain facts discussed in Section 4, permanent gases 
like argon are preferable in such an analysis; nonper- 
manent gases like helium, ozone, water vapor, etc., 
must be compared to permanent gases in order to ascer- 
tain the location and characteristics of sources and 
sinks. 
Difficulties encountered in the mathematical analysis 
of time-varying one- or three-dimensional diffusion must, 
of necessity, confine the discussion to simplified models 
of the processes. More thorough and critical considera- 
tions than before appear necessary in order to avoid 
misleading results owing to oversimplification of the 
models used. 
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