528
SAUCIER, HALL, AND NELSON
humidity during the spring season, Weather radars are operated at
the Oklahoma City airport, Tinker Air Force Base southeast of Okla-
homa City, NSSL in Norman, Wichita Falls, and Fort Worth. At most
of these, photographic scope records are made for later research use.
An M-33 radar system at Norman is also employed by this project for
current storm surveillance and for obtaining wind soundings in the
thunderstorm surroundings.
During the 1963 storm season, we maintained rainfall collectors
situated over the northwest one-third of the network. These were pans
of 25 sq ft area which emptied into 10-liter plastic jugs. With this
surface area of the pan, a rainfall of 0.15 in. gave a 10-liter sample,
which was believed to be more than sufficient for the radiochemical
analyses planned. Under each pan, a dry filter paper, which was exposed to the air but sheltered from the rain, was placed horizontally to
collect a sample of the dry fallout. This was to serve as an index to
the dry fallout collected by the pan which would contaminate the sub-
sequent rain sample. Each time the pan was washed, by either hand or
rainfall, the filter paper was changed. The radioactivity of the filter
paper was found to be below threshold in each case. Therefore the
procedure for observing dry fallout was discontinued in 1964.
Analysis of the 1963 data revealed that the radioactivity, as well
as the rainfall, varied considerably from one collector to the next, even
though the sample collected by any pan was a composite of the entire
storm over that location. This was attributed to the existence of significant horizontal gradients in radioactivity within the storm produced
by variations in the storm circulation of dimensions equal to or smaller
than the collector network. Also, propagation of the storm would pro-
duce local time variations in the amount of radioactivity collected. To
obtain meaningful results required a sampling technique that would
measure the time variations at each station. These time variations
measured at each in a network of collectors, compared with the in-
tensive meteorological records for the storms, would lead to a more
complete picture of the circulation, propagation, and development of
the storm. The rain-sample collector pans were modified so that each
would obtain as many as ten 1-gal sequential samples of rainfall per
storm. A 1-gal sample represents about 0.05 in. of rain. The tenth
sample at each collector integrated all rainfall from the storm beyond
about 0.50 in. Some loss occurred between samples due to strong winds.
The automatic sample collector was designed by S. J. Hall from
the pattern devised earlier by the Illinois State Water Survey group.
Figure 4 is a photograph of the original collector pan on the left and
of the automatic sequential sample collector on the right. As each jug
in sequence is filled to the desired level, it drops by its weight, and
the next jug is driven into position by torque on the axial drum sup-
plied by a pulley and weight system. The weights are common build-