Daily fluctuations of radioactive fallout particles in ground-level air

Long-range 500 mb and 300 mb air trajectories were computed in an attempt to interpret the daily variation of the number of fallout particles in the ground-level air observed at Fayetteville (36°N, 94°W), Arkansas, after a nuclear weapon was tested at Lop Nor (40°N, 90°E), China, December 24, 1967. The dates of occurrence of peak concentrations of fallout particles generally coincided with (a) the arrival times of air masses at 500 mb and/or 300 mb after completing a cycle around the world, and (b) the passage of 500 mb troughs at Fayetteville. A significant deviation from the above rule occurred on January 20, 1968, when the highest concentration of fallout particles in air was observed at Fayetteville. According to the computed air trajectories, such a maximum should have occurred 3 days earlier on January 17, 1968. The discrepancy was explained as due to local meteorological conditions: the occurrence of positive vorticity transport at 500 mb followed by the formation of slow-moving cut-off low during January 17 through January 19, 1968.