Effect of atmospheric wind structure on shorter-period, nuclear-generated infrasound

Abstract

One of the outstanding characteristics of acoustic signals received from nuclear explosions is their great time duration. This is true for long-period waves (greater than 1 minute), for intermediate-period waves (about 1 minute), and for short-period waves (less than 1 minute). Furthermore the extended signal often contains a very great number of (apparent) pulses of 10–20-sec duration. Ordinary dispersion cannot account fully for either the duration-effect or the multipulse appearance. This paper suggests that for intermediate periods the extended signal duration may be due to horizontal refraction from large-scale weather fronts. The change in travel time due to this horizontal refraction can account for the signal duration. It appears that the multipulse short period behavior may be a diffraction effect. It is shown that the very commonly occurring wind ducts, with wind speeds of 3 m/sec and several thousand feet thickness, can ‘split’ the pulse hundreds of times by diffracting the pulse. Such splitting into a transmitted and a reflected portion occurs for component time periods of 10–20 sec. This splitting and the attendant delay may account for some of the shorter-period signal characteristics.