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THATCHER, PAYNE, AND CAMERON
of year. With the onset of the monsoonin June, the tritium level dropped
sharply to average 188 T.U. for the four months of the monsoon season.
This is approximately one-tenth of the level at Teheran during these
months. In 1963 the same pattern is repeated at the somewhat higher
tritium level of 246 T.U.
Bombay shows the same pattern as New Delhi but with more
pronounced oceanic influence. Minicoy, an island off the southwest
coast, had an average level of 167 T.U. in the 1963 monsoon season.
This is only 79 T.U. lower than New Delhi and shows the complete
dominance of the oceanic air masses deep into the continent in the
monsoon season. In 1963 New Delhi (246 T.U.) had a lower level than
Bombay (464 T.U.) during the monsoon. This is the reverse of ex-
pectations. The
situation is attributed to the 1963 monsoon coming
predominantly from the Bengal Sea, whereas in 1962 it came pre-
dominantly from the Arabian Sea.
Tritium levels at Diego Garcia (IA), an island in the Indian Ocean
at 06°34’S, show the typical low values of the southern hemisphere.
The average for 1963 was 34 T.U.
The Pacific Ocean
In the Pacific, tritium data have been obtained ata series of
stations ranging from 51°35’N, Adak, Alaska, to 41°S, Kaitoke, New
Zealand. Here the sampling sites are clearly dominated by an oceanic
environment; and, consequently, as a group the tritium concentrations
at the northern-hemisphere sites are substantially lower than in the
other four northern-hemisphere areas considered in this report.
The highest concentrations are found at Adak (CR) and Pohang
(IA), at Adak because of the high latitude and at Pohang because of the
nearby Asian continent, which provides a continental air-mass effect.
Tokyo, at approximately the
same latitude as
Pohang,
shows con-
sistently lower concentrations.
Comparison of the 1963 tritium data at the Pacific islands, Midway
(LJ) (28°N), Hawaii (LJ) (19°44’N), Johnston (LJ) (16°44'N), indicates
a significant latitude trend. All three sites are completely oceanicdominated, and therefore the latitude effect can be revealed without
ambiguity. The mean values for the February through September 1963
data are given below. Data for Tokyo and for Adak (based on an assumed 1500 T.U. for August and September) are also given.
Station
Latitude
T.U.
Adak
Tokyo
Midway
Hilo
51°53'N
35°41'N
28°13’N
19°44’N
2030
876
351
204
Johnston
16°44’N
155