A Radio-Active Fall-Out Study at Melbourne, Australia

Measurements of the radio-active fall-out occurring in weekly rainfall samples at Melbourne (Aspendale) are presented for the period June 1958 to February 1959. Radio-active decay analyses show the activity to have arisen from nuclear weapons tests carried out near the equator during the period April to September 1958. The results indicate that, despite presumably continuous dispersion, individual radio-active clouds maintain their discreteness and a limited E—W extent even after six or nine months residence in the stratosphere. This property allows a poleward drift speed of order 1 m/sec and zonal circulation velocities ranging from 6 to 17 m/sec to be inferred.