Temporal Changes in Horizontal Diffusion Parameters of a Single Nuclear Debris Cloud

Abstract

An evaluation is made of the variations of σy and KH over a 70-hr period as derived from analyses of radiological and meteorological data collected during extensive aerial sampling of a single nuclear debris cloud. These data reveal that for t<1 hr and t>10 hr, σy?T0.5 and KH≈constant; however, for 1<t<10 hr, the diffusive process is accelerated so that σy?T1.2 and KH≈σ1.17y.A constant-diffusivity model for the Ekman layer, developed by Csanady, is assessed. The model yields close approximations to σy through the period of ?shear-induced? diffusion between 1 and 10 hr after detonation. In both cases the constant-diffusivity model is highly dependent on U2g