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HUFF
junction with a research program on the rainout of radioactivity in
convective rainstorms. This research was performed to determine the
time and the space distributions of storm rainout and the relation of
these distributions to various meteorological factors. This paper is
restricted to discussions of space distributions.
Two major purposes of the Illinois research were to determine
quantitative relations for the spatial variability of radioactive rainout
in convective storms and to ascertain the accuracy with which a point
radioactivity measurement represents the mean storm rainout for
areas of various sizes. Such knowledge has important applications in
investigations aimed toward defining the atmospheric processes and
the hydrometeors controlling the radioactive rainout in rainstorms and
in the design of sampling networks for health-hazard monitoring. The
sampling-network problem will become increasingly importantif large
increases in fallout occur in the future. Another problem that has not
been satisfactorily solved to date is the relation between radioactive
rainout and rainfall parameters; that is, how well can the rainout be
estimated from a knowledge of the volume, the intensity, and the dura-
tion of the associated precipitation and how similar are the areal
patterns of radioactive rainout and rainfall.
Through use
of data collected on densely gauged networks in
Illinois, considerable information on the mesoscale features of radioactive rainout has now been compiled and is presented in this paper
for
the
use of persons and organizations involved in radioactive-
fallout projects. It is not implied that the Illinois study provides
complete answers to the several problems that exist, but the results
do supply considerable quantitative information not available previously.
Furthermore, the results clearly illustrate how erroneous conclusions
may be reached when the characteristics of radioactive rainout are
based upon data assembled from widely spaced observation points.
MEASUREMENT PROCEDURES
During 1962 storm-rainwater samples were collected for radiochemical analyses in the three concentrated rain-gauge networks shown
in Fig. 1. The East Central Illinois network consists of 49 recording
rain gauges in 400 square miles, the Kaskaskia network hasfive re-
cording rain gauges in 12 square miles, and the Boneyard network
consists of 11 recording and ninenonrecording rain gaugesin 10 square
miles. These concentrated rain-gauge networks provided a detailed
pattern of the time and the space distribution of the amount, the intensity, and the duration of rainfall within the area.
On the East Central Illinois network, rainwater samples were
obtained from weighing-bucket rain gauges, most of which had 12.6-in.-