650
THATCHER, PAYNE, AND CAMERON
globe:
Europe and the Mediterranean, Africa and surrounding ocean
areas, South Continental Asia and the Indian Ocean, Eastern Asia and
the Pacific, and the Americas.
The data cover 1961 through early 1964. It is generally arranged
in the five tables on a north to south basis with a few exceptions. Approximately one-half of the network stations are represented. The
other stations are not represented for various reasons: failure to
receive the samples, contamination of samples making them unfit for
measurement, or insufficient measurements.
The figures plot the concentration—time trends for key stations
in each of the five global subdivisions and provide a basis for intercomparisons between individual stations and regions.
The most striking observation is the general similarity of trends
in tritium concentration throughout the northern hemisphere. While
the absolute concentrations vary from site to site, the same relative
concentration changes in precipitation are observed at almost all sites
in the northern hemisphere. The exceptions to the overall pattern are
found in sites where the seasonal climatological pattern is affected by
extraordinarily powerful influences, as in the monsoon region of India.
The consistency of the overall pattern strongly suggests that the
major control on tritium fallout is stratospheric rather than tropospheric. The stratospheric control regulates the major phases of the
tritium cycle, and the tropospheric controls affect only the relative
variations betweensites.
Tritium at all stations rose sharply in November and December
1961 following the release of 95 Mt of fusion by the U.S.S.R. in late
October 1961. The base in September and October 1961 was approximately 80 T.U. for continental sites in the mid-latitudes and 20 to
40 T.U. for sites influenced by oceanic air. In November and December
the tritium concentration of precipitation rose to an average of ap-
proximately 200 T.U. for continental sites as a result of tropospheric
fallout.
The tritium rise continued in early 1962 to attain a peak of approximately 1000 T.U. at continental mid-latitude sites by March.
Further rise continued to approximately 2000 T.U. at several sites and
remained at this level through July or August. Decline was apparent
in September, and minimum levels were generally reached in October
or November. The minimum for 1962 was approximately 400 to 500 T.U.
In 1963 the pattern established in 1962 was repeated with a general
rise in January which continued to peak levels in May which were sus-
tained through July or August. The peak was higher than in 1962,
averaging 4000 to 5000 T.U. for continental sites. At Some northern
sites concentrations of 8000 to 10,000 T.U. were observed. For tritium,
1963 appears to have been the peak fallout year. The October or No-
vember minimum wasin the range of 1000 T.U.
(Text continues on page 659,)