HF radio measurements of high-altitude acoustic waves from a ground-level explosion

Linear acoustic theory predicts that a large ground-level explosion—several hundred tons of TNT—should produce a pressure wave amounting to several per cent of ambient in the atmosphere 200 km above the explosion. Analysis of the interaction of such a pressure disturbance with the ionosphere implies that the passage of the wave should be readily measurable by means of vertical-incidence radio phase-path soundings. Radio measurements made at the time of a 500-ton explosion have confirmed the hypothesis. The shape of the observed phase disturbance agrees well with that predicted, and the observed onset times check to within 10 seconds with acoustic ground-to-ionosphere travel times. The amplitude and duration of the disturbances were approximately 100 radians and 2 minutes, respectively. The amplitude is slightly smaller than predicted; however, the observed duration is approximately twice that calculated. Refining and fitting the model to obtain better agreement—especially in disturbance onset time, shape, and duration—may represent a technique for improving present estimates of the upper-atmosphere density molecular weight and temperature.