BOD Q hl ies
SSE STEER EAPDT TELL
RADIATION STANDARDS, INCLUDING FALLOUT
61
gists are therefore not in unanimous agreement on the stratospheric circulation and mixing processes—neither on the qualitative nor the quantitative
aspects of transport within or removal from the stratosphere.
PREDICTIONS
The payoff in the meteorology of fallout is an accurate prediction of the fate
of an arbitrary injection of debris anywhere in the stratosphere. The previous
discussion indicates that this is not possible on purely meteorological grounds.
Hence, the fallout forecasters almost all extrapolate from past experience and
their own intuition. It should be noted, however, that some of the models will
predict the same fallout pattern even though their details may differ significantly.
By way of illustration and because of current interest, the last few moments
of this talk will be devoted to a set of predictions for events of current interest.
Figure 16 shows zones of the stratosphere in which nuclear clouds may have
essentially the same history. For example, the lower polar and temperate
zone stratosphere up to about 80,000 feet will be characterized by fast fallout
deposited in the same hemisphere as the injection. These features are derived
from past polar injections. It is the present view that stratospheric clouds
injected as far equatorward as 30° may behave like the polar clouds. Injections at the Equator, like the current U.S. tests at Christmas Island—those whose
nuclear clouds reach only to 80,000 feet—are in the zone identified on the
placard as lower equatorial B. It is characterized by somewhat slower removal
and roughly equal partitioning between hemispheres. There have, of course,
been injections into this zone by United Kinglom tests prior to 1959 but the
lack of unique tracers and confusion of the United Kingdom debris with other
fission products prevents one from actually using the history of the United
Kingdom fallout in future predictions. The forecasts are, therefore, based on
experience from the U.S. Eniwetok tests and meteorological intuition.
Figure 17 shows a cross section of the geographical spread of fallout for equal
inputs into the two zones—for simplicity to be called the polar (Soviet) and the
equatorial (United States). The Soviet fallout is shown to be limited primarily
to the Northern Hemisphere with a temperate zone peak while the U.S. fallout
is distributed about equally into both hemispheres with lesser peaks in each
temperate zone.
Figure 18 displays the time history of the fallout. The horizontal axis is time,
in years, increasing toward the right and monthly deposition increasing upward
on the vertical axis. The lower polar fallout, indicated by the dotted line, comes
down virtually entirely in the first year, while the U.S. fallout, indicated by
the dashed line, takes many years for the same amount to be deposited. In both
cases a spring maximum is expected.
Figure 19 repeats the lower equatorial curve dashed line in figure 18 but
adds a dotted line for a case of fallout from a different zone. This is from the
5
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very high atmosphere zone in figure 16 such as the clouds from high altitude
nuclear rocket detonations. Experience from the 1958 Johnston Island events
marled with rhodium 102 forms the basis for these predictions. The fallout
from these high-altitude injections will partition about equally between hemi-
spheres and likewise peak in the temperate zones. But the time history given by
the dotted line shows the much slower rate of fallout; in fact it may take a whole
year before even the first fallout is received at ground level.
CON CLUSION
tre
Experience derived from fallout since 1959 permits more confident predictions of fallout from many kinds of stratospheric injections. But the meteorology
explaining the observed fallout still lags behind the empirical findings.