Effects of relative humidity and yield on self-induced rainout from tactical nuclear explosions

Abstract

We have studied the process of wet fallout from a tactical nuclear explosion due to scavenging of radioactivity by self-induced rain (rain produced by the explosion itself) using a numerical two- dimensional model of an axisymmetric cloud. Under mid-latitude summertime conditions and for yields of 20 to 100 kilotons, the model shows that self-induced rainout is not significant for low relative humidities, is very important for high relative humidities (> 80%), and is moderately important for relative humidities down to about 50%. When self-induced rainout occurs, it is heavy within a couple of kilometers of ground zero and peaks early in the episode. The model has successfully predicted observed radioac tive self-induced rainout for the Hiroshima and Nagasaki detona tions (both in the 20 kiloton range), and does not predict rain under conditions typical of U.S. tests in Nevada, where self-induced rainout has not been observed. The model is interesting as a hybrid of Eulerian and Lagrangian methods.