RAINOUT RELATIONS ON SAMPLING NETWORKS
913
Table 2— CORRELATION BETWEEN GROSS BETA RELATIVE
VARIABILITY AND RAINFALL FACTORS ON
KASKASKIA AND BONEYARD NETWORKS
Correlation
factor
Beta-concentration variability vs. mean storm rainfall
Beta-deposition variability vs. mean storm rainfall
—0,32
—0,45
Beta-concentration variability vs. storm-rainfal] duration
Beta-deposition variability vs. storm-rainfall duration
—0.20
—0.33
Storm-rainfall variability vs. mean storm rainfall
Storm-rainfall variability vs. storm-rainfall duration
-—0.25
— 0.30
Table 3—-RATIO OF MAXIMUMTO MINIMUM VALUES OF GROSS
BETA ACTIVITY AND STORM RAINFALL
Fifteen-storm ratios
Mean
Median
Maximum
Beta concentration
2.7
2.3
9.5
Storm rainfall
1.8
1.5
4.0
Beta deposition
2.5
2.0
6.8
Minimum
1.4
1.3
1.1
indicates that gross beta activity has more extreme variation in storms
on the average than does storm rainfall. This is in agreement with the
average relative variability data of Table 1. Gross beta deposition was
found to vary slightly less areally than did concentration. The betaconcentration ratio equaled or exceeded the rainfall ratio in 12 of the
15 cases, and the beta-deposition ratio was greater than the rainfall
ratio in 11 of the 15 cases. The average relative variability of both
beta concentration and beta deposition exceeded average storm-rainfall
variability in 12 out of 15 cases (Tablel). Thus the foregoing statistics
indicate a strong tendency for greater areal variability in gross beta
activity than is exhibited by storm rainfall. In turn, this suggests
partial control of rainout of radioactivity by other atmospheric factors
with relatively large spatial variability. It seems logical to expect the
surface rainout to be related to the drop size distribution in the storm
clouds in which the rainfall developed; this distribution should be highly
variable in the convective storms that make up the 15 samples used in
the variability study. Regardless of the cause, however, the study
indicates that great variability in rainout of radioactivity may occur
within small areas of 10 to 15 square miles and within distances of 1
to 2 miles in midwestern convective storms. If this degree of varia-