Evidence for Short Temporal Atmospheric Variations Observed by Infrasonic Signals: 2. The Stratosphere

Abstract

Low-frequency sound waves, also known as infrasound, propagate in the atmosphere at frequencies ranging from 0.02 to 20 Hz. Their propagation is affected by temperature and winds, which vary spatially and temporally. Efficient propagation conditions arise when the combination of temperature and winds forms atmospheric waveguides. Such waveguides facilitate infrasound propagation over hundreds and thousands of kilometers (Evers & Haak, 2010).Infrasound is used for the forensic analysis of events, which can be both natural and anthropogenic. For forensic applications, numerical simulations are often used to help interpret the observations. Simulations are based on realistic atmospheric conditions, which are the product of numerical weather prediction (NWP) models. The weather forecast agencies provide such models at best every 1 hr. Since the atmosphere is a dynamic system, it is continuously changing, and therefore the acoustic propagation conditions change too. Hence, simulated signals using weather prediction models and observed wavefields can be significantly different (Averbuch et al., 2022).Alternatively, infrasound monitoring can be used to probe the atmospheric temperature and winds. While a wide array of technologies measure the lower and upper regions of the atmosphere, the middle atmosphere (30-80 km) is less sampled; this is a result of technological challenges that limit in situ and indirect measurements (S. Kulichkov, 2010;Lee et al., 2019). Since infrasonic waves propagate in these regions, exploiting them to probe the middle atmosphere has been the focus of multiple studies. For example, infrasound characteristics such as travel time, back azimuth, and apparent velocity have been used to quantify atmospheric winds by direct calculations and probabilistic inversions (

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