The upper portion of the Hadley cell circulation as deduced from the 1968 French and Chinese nuclear tests

French and Chinese nuclear testing in 1968 provided an opportunity for studying stratospheric transport processes. The French tests of August and September 1968 and the Chinese test of December 1968 provided radioactive tracers to follow air motions in the lower stratosphere of each hemisphere. The two sources are readily distinguishable by fission product ratios (e.g., Zr-95/Ce-144). Information on interhemispheric exchange in the upper troposphere and lower stratosphere has been developed by the analysis of air-filter samples obtained by aircraft and balloons. The meridional transport of radioactive debris into the lower equatorial stratosphere from two sources is qualitatively explained by a mean meridional circulation superimposed on large-scale mixing processes. It is further suggested that the mean circulation is an extension of the tropospheric Hadley Cell into the lower stratosphere.