STRATOSPHERIC DISTRIBUTION OF NUCLEAR DEBRIS
317
The distributions of “Sr during January to April 1963 and May to
August 1963, shown in Fig. 12, are based on more substantial data. The
high concentrations of ‘Sr in the northern polar stratosphere resulted
from the injection of debris into that region by the late 1962 U.S.S.R.
test series, including the December 1962 tests. It is unlikely that the
zonal distribution of the debris from these tests was uniform as yet.
The subsequent rapid drop in concentrations of debris in this region
suggests that the ‘Sr concentrations sampled during early 1963 were
anomalously high. The somewhat lower concentrations found during
May to August 1963 may have been more representative of the average
values in the stratosphere. Since few data are available for the Sr
concentrations in much of the southern polar stratosphere during the
first two-thirds of 1963 and since none are available for the upper
tropical stratosphere, the distributions that are shown in these regions
in Fig. 12 may be in error. These distributions are based on several
assumptions. One is that the high concentrations of *°Sr (greater than
100 dis/min per 1000 scf) found at 105,000 ft at Mildura during January
to
April 1963 were derived from high-altitude injections,
such as
Starfish Prime. Another assumption is that most of the *°Sr found at
90,000 ft at Mildura during May to August 1963 had moved southward
to 34°S from the tropical stratosphere.
The sr distributions during September to December 1963 and
January to April 1964 (Fig. 13) show continuing decreases in the *°Sr
concentrations in most regions of the stratosphere. The decreases
that occurred in the concentrations in the region above 90,000 ft between mid-1963 and early 1964, as we discussed previously, seem to
be attributable only to settling of fallout particles from that region into
the lower stratosphere. It may be noted that this same mechanism could
be used to explain the changes in stratospheric concentrations that
occurred during the 1958 to 1961 moratorium on weapons testing.
The horizontal profiles of *Sr at 65,000 ft which are plotted in
Figs. 14 to 16 mayaid in the visualization of the changes that have occurred in the "Sr distribution during 1962 to 1964. Between August 1961
and March 1962 (Fig. 14), the ®Sr concentrations increased in the
northern hemisphere as a result of the 1961 U.S.S.R. tests. By July
1962 the peak concentrations, attributable to the Dominic I tests, were
found in the tropical stratosphere. The high concentrations of Sr pro-
duced in the northern hemisphere by the 1962 U.S.S.R. tests resulted
in the presence of a steep concentration gradient across the tropical
stratosphere by January 1963. This gradient was still quite steep in
July 1963 (Fig. 15), but it had decreased considerably by October 1963
as a result of the movement of debris from the northern into the south-
ern hemisphere. The gradient was about the same in January 1964
(Fig. 16), but by May 1964 it appeared again to have becomestill more
gentle, perhaps because of more debris entering the southern hemi-