ATMOSPHERIC TRANSPORT PROCESSES LEADING TO RADIOACTIVE FALLOUT OVER THE UNITED STATES IN NOVEMBER 1962 ELMAR R. REITER and JERRY D. MAHLMAN Colorado State University, Fort Collins,*Colorado ABSTRACT Radioactive fallout in excess of 320 pc/m? of air was observed over the South Central United States Nov. 24 to 27, 1962. Atmospheric transport processes leading to these abnormally high values of fallout were studied in detail. It was estimated that 0.6 x 10" metric tons of air were involved in the rapid sinking process that transported air from the tropopause level to the ground in a matter of approximately two days. Wet washout processes also removed some radioactive debris from the atmosphere. INTRODUCTION It has been established by a number of case studies’ ® that atmo- Spheric motions, especially in the jet-stream region, are capable of rapidly transporting downward radioactive debris from the tropopause or the lower stratosphere to the ground. The purposes of the study reported in this paper wereto (1) arrive at quantitative estimates of the efficiency of such transport processes in the removal of stratospheric debris and (2) derive, if possible, fore- casting procedures for stratospheric fallout based upon dynamic considerations. These objectives were achieved by a detailed analysis of a case of strong radioactive fallout over the South Central United States which occurred Nov. 24 to 27, 1962 (see Fig. 1), The motion of 450