RELATION OF UPPER AIR HEMISPHERIC INDEX
PATTERNS TO SEASONAL FALLOUT FLUCTUATIONS
JERRY D. MAHLMAN
Colorado State University, Fort Collins, Colorado
ABSTRACT
The downward transport of radioactive debris from the stratosphere,
in connection with tropopause-level cyclogenesis, is considered as a
possible
physical explanation for the spring fallout maximum. To
examine this possibility, an index designed to measure the relative
amount of cyclonic activity in the atmosphere is derived and then
compared with seasonal variations in mean fallout intensity. It is
established from the analyses that the spring fallout peak cannot be
adequately explained by an increase of cyclonic activity at this time of
year. It appears, however, that shorter period fallout peaks, super-
imposed upon the mean seasonal curve, are related to the occurrence
of cyclogenesis in the upper troposphere.
INTRODUCTION
In nearly every year since about 1955, a spring maximum of surface radioactivity resulting from nuclear testing has appeared in the
northern hemisphere.’ This spring peak is distinct from the heavy
fallout that follows shortly after periods of heavy testing in the atmosphere. The fallout maximums which occur soon after these testing
periods are in accordance with the assumption that the mean tropospheric residence time of radioactive debris is of the order of one
month. Because the spring peaks often occur many months after the
termination of atmospheric nuclear testing, it is necessary to postulate
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