Abstract
The relation between radioactive fallout and meteorological conditions was studied. The relation of rainfall amount to fallout (R) can be expressed fairly well by the formula R=C (1-e-βP+κP), where P is the amount of rainfall, C is the air activity,β and κ are constants. There is little correlation between the surface weather conditions and fallout while a considerably higher correlation was found among a trough at 500 mb, position of jet stream and air activity. The activity increases remarkably when a trough at 500 alb passes above, and a core of jet stream is located above or a little south of an observation point. The analytical results of Sr-90 deposition in Japan since 1954 and its seasonal variation were also discussed.
