Evidence for short temporal atmospheric (tropospheric) variations observed by infrasonic signals

Infrasound monitoring is used in the forensic analysis of events, to study the physical processes of sources of interest and to probe the atmosphere. The dynamical nature of the atmosphere and the use of infrasound as a forensic tool lead to the following questions: (1) what is the time-scale of atmospheric variability that affects infrasonic signals? (2) can we link variations of infrasound signals to specific atmospheric phenomena? This study addresses these questions by monitoring a repetitive infrasound source and its corresponding tropospheric returns 54 km away. Source-receiver empirical Green's functions are obtained every 20 s and used to demonstrate the effect of atmospheric temporal variability on infrasound propagation. In addition, observations are compared to predicted simulated signals based on realistic atmospheric conditions. It is shown that infrasound properties change within tens of seconds. Particularly, phases can appear and disappear, the propagation time decreases, and the signals' energy fluctuates. Furthermore, the similarity between the predicted and observed signals varies significantly within a few minutes. The observed changes are related to variations in temperature and wind, which are coupled to dynamic processes such as radiation, gravity waves, and turbulence. Therefore, this study highlights the potential of high temporal infrasound-based atmospheric sounding.