RELATION OF INDEX PATTERNS TO FALLOUT PEAKS
469
debris intensity was relatively high as a result of heavy testing prior
to the test ban,
Since fallout maximums tend to appear in relation to tropopause-
level cyclones,’:’.!°,11 300 mb was chosen as the most representative
level for the calculation.
Because the maximum cyclonic intensity
generally occurs within the 40 to 60°N latitude band, 50°N was chosen
as an appropriate latitude for the calculation of a series of cycloneindex values. Also, since the United States provides the only fallout
network that gives values representative over a large area, the index
was calculated from 70°W to 110°E longitude instead of around the
entire hemisphere.
If
Eq.
10
is
applied
to
the atmosphere under the previously
specified conditions, a difficulty arises because the flow direction is
often nonsymmetrical with respect to a given longitude line. In theory,
this could be avoided by driving the cyclone index in terms of a more
complicated atmospheric current that incorporates the tilting of
troughs, /8:17 This approach, however, increases the complexity of the
derivation
of
C considerably. These problems resulting from the
asymmetry of the current were in part avoided by measuring a mean
@ over the 10-degree latitude interval of 45 to 55°N instead of taking a
point value at 50°N,
By
an
incorporation of the previous specified conditions, the
cyclone index was calculated at 24-hour intervals for the period of
January to October 1963. Computational noise and the higher frequency
components were filtered from the time series by uSing a weighted
smoothing technique." See Fig. 1. By independent cross-checks the
cyclone index was seen to provide a statistically reliable indication of
the relative amount of cyclonic activity in the atmosphere. The index
was also checked by calculating separate time series with the use of
the 00 GMT and the 12 GMT data, respectively. The major fluctuations
in the two resultant smoothed time series were identical. The calculated filtered index time series for the indicated period showeda
succession of index increases terminated by index drops of equal
magnitude.
RELATION OF THE INDEX SERIES
TO THE FALLOUT DISTRIBUTION
The time distribution of fallout in air over the United States was
determined by computing area-weighted averages of gross betaactivity
in picocuries per cubic meter of air from the U. S. Public Health Radiation Surveillance Network. Two distinct scales of fallout intensity
with respect to time were obtained by calculating five-day and monthly
averages of the mean area-weighted fallout intensity (see Fig. 1). This