Some Notes on Discrete Trains of Infrasonic Waves Produced by Point Sources

Abstract

The most prominent trains of infrasonic waves are produced by strong point disturbances in the atmosphere, such as nuclear explosions in the megaton range. The infrasonic records at the La Paz Bolivia observatory indicate that the signals resulting from such explosions have a sharp beginning similar to seismic records. The results of analysing the data from four signals presumed to have resulted from nuclear explosions in the atmosphere are given in Table 1. The great circle path length from the source location to La Paz, and the arrival times for the short and long path arrivals are also given in the table. The long path arrival for all events, except that of 1968 August 24, was somewhat masked by the irregular noise at the tail of the short path signal. Readings on all received signals were taken at four distinct times. Values are not given for some readings on the long path arrivals, due to low signal conditions. The periods given in the table indicate normal dispersion properties, with the very long period gravity waves arriving first. The remaining readings appear irregular both in period and in travel time, with no distinct wave arrivals noted. The observed dispersion is somewhat dependent on the size of the explosion exciting the waves, but a greater influence is the wind and temperature variation with altitude. Seasonal effects are evidenced by observing the travel time for the events of 1968 December 27 and 1970 October 14. The difference between the short and long path arrivals is changing, probably due to different seasonal wind profiles.