RAINOUT RELATIONS ON SAMPLING NETWORKS
919
AREAL-PATTERN RELATIONS
Comparisons were made between the areal patterns of rainout of
radioactivity and rainfall on the networks in 1962 and 1963 storms. It
is quite possible for point-to-point correlations to be poor, whereas
areal patterns may show considerable similarity. For example, high
and low regions in the rainfall and radioactivity patterns would be dis-
placed from each other if the greatest concentration of radioactivity
tended to occur near the edge of convective rain cells rather than near
the cell center. Other factors, such as storm movement and raindrop
fall velocity, may also cause displacement of high and low centers of
radioactive rainout and rainfall from each other. With such conditions
correlation coefficients from point data might be relatively low, although
a definite physical relation was apparent in the areal patterns.
Comparison of the areal patterns of beta rainout and total storm
rainfall on the East Central Illinois network in 1963 revealed a rela-
tively strong association between the patterns of beta deposition and
storm rainfall, with respect to the location of highs and lows in the
patterns, in seven of nine storms in which data were available to define the patterns accurately. In no case was the spatial displacement
of centers greater than six miles when the pattern association was
rated strong. In all cases regions of heavy beta deposition tended to
be associated with regions of relatively heavy rainfall, and light rain-
fall was associated with light deposition. The areal patterns of beta
concentration and storm rainfall did not compare as favorably as the
patterns of deposition and rainfall. The association of patterns was
relatively strong in six of the nine storms, but the high and low as-
sociation was not consistent. High beta concentrations occurred in
low rainfall regions in five of the six cases, whereas, in the other
case, the association was strong but high beta concentrations were
associated with high rainfall values. Huff! has indicated that the occasional reversal from a direct to an inverse relation between beta
concentration and rainfall is dependent upon the maturity of the storm
system and its degree of vertical development.
An example of pattern associations is illustrated in Fig. 4 for the
storm of July 1 on the East Central Illinois network. Relatively high
beta concentrations in the northern and the southeastern parts of the
network correspond with relatively light rainfall in these regions. A
region of relatively light beta concentration extends from the eastern
to the southern part of the network, but it is displaced about three
miles east of the corresponding rainfall high in the south-central part
of the network. Similarly, generally close association is indicated between regions of highs and lows in the beta deposition and the rainfall
patterns, although the high centers are displaced from each other by
several miles.