Gravity and rumble of distant sources

Abstract

The subject of this paper is the comprehension of this physical phenomenon: Let an atmospheric source emiting an impulsive signal (such as thunder, explosion...). The received signal at short distance is itself impulsive but at long distance one can hear a rumble which can last up to one minute. If one models the propagation of the sound by the traditional equation of the waves, as the Green function is a distribution whose support is the sphere of radius CT (C: speed of sound, T: the travel time), the received signal (calculated by convolution) should last only the duration of emission. If one uses ray tracings to take into account the heterogeneity of the medium, one obtains the same conclusion (only the time of arrival is modified) in contradiction with the experimental results such as those obtained for example during the First World War to detect the position of the enemy batteries. A similar phenomenon can be observed in the study of the propagation of a sonic boom (although less obvious because the support of the two-dimensional Green function is not a circle). We thus propose a critic of the physical models, and our conclusion lays on the need for taking into account gravity.