solution will contribute substantially to knowledge of stratospheric circulation.
Two obvious experimental
approaches are direct investigation by high altitude sampling and the use of selected atmospheric tracers.
Someof the fallout evidence having bearing on the question of high stratosphere holdup of nuclear debris
from past tests are presented and discussed below.
Cloud Height Considerations
The development and rise of nuclear clouds and the influence of meteorological factors on their height
9
10
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tas
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:
and shape have been discussed by Machta and Kellogg.
Approximate stabilization cloud heights for equatorial surface bursts of several yields, based on results of Kellogg,
1
° are given in Table 1.
“7:
Time of stabili-
Table 1
Approximate Stabilized Cloud Heights for Equatorial Surface Bursts
Height, Center
(ft)
Vertical Extent
(ft)
Height, Top
(ft)
10 MT
82, 000
46, 900
105, 000
1 MT
63, 000
28, 000
77,000
100 KT
40, 000
16, 000
48, 000
50 KT
34, 000
12, 000
40, 000
Yield
zation apparently increases somewhat with yield, but is usually taken as 6 minutes,
For megaton yield shots,
horizontal growth continues to 10 minutes or longer at a rate too rapid to be due to natural wind shear. 10 The
observational data for megaton burst clouds are inadequate to reliably assess the vertical extent and heights of
cloud tops at times beyond the first few minutes.
Subsequent vertical extent due to meteorological mixing on a
time scale of weeks and months is unknown.
Considerations about debris condensation, particle growth and cloud distribution have been discussed by
the Rand Corporation! and by Lapple. 2
Lapple argues convincingly that the radioactive debris cannot be
restricted to a discrete small portion of the cloud volume, but must be distributed generally throughout the
cloud,
However, in stratospheric clouds for high-yield surface shots, the upper portion of the cloud should
exhibit higher activity concentration, a greater proportion of the very fine particles which persist in the
stratosphere, and some enrichment in fission products like sr’? and cg l3? which condense late from gaseous
or volatile precursors.
Subsequent upward migration of the more concentrated zone of the debris cloud on a
time scale of hours, days, and longer, may occur under the influence of local heating from residual radiation
and from debris absorption of radiation from external sources.
The evaluation of these as well as meteorologi-
cal factors which may modify the vertical distribution of nuclear debris clouds following stabilization appears to
be a neglected subject.
U-2 aircraft, used in the High Altitude Sampling Program, 2,8 provide excellent means of sampling up to
levels of 70,000 feet.
However,
it is clear from the cloud height data, Table 1, and from other considerations
mentioned above, that a substantial proportion of debris from megaton-yield tests was injected to higher levels.
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