The effect of the stratopause on the structure of the infrasound signal from the August 4, 2020, Beirut explosion

Abstract

The influence of wind velocity and temperature stratification in the upper stratosphere on the waveform of the infrasound signal received at a distance of 2398 km from the epicenter of the powerful explosion in Beirut that occurred on August 4, 2020 is studied using ray trace and pseudo-differential parabolic equation (PDPE) methods. Given a high temporal variability of the wind velocity in the stratopause predicted by the European Centre for Medium-Range Weather Forecasts model, it is assumed that within the stratopause layer, the increase in effective sound speed with increasing height is very small, on the order of 1 m/s. When modeling propagation of the signal from the explosion, the presence of a fine-scale layered structure of wind velocity and temperature in the real atmosphere was also taken into account. Accounting for the scattering of infrasound by strongly anisotropic (layered) inhomogeneities of the effective sound speed allowed us to explain the appearance of “fast” stratospheric arrivals, their time durations, the time period between successive arrivals (about 110 s), and the waveform of the entire observed signal.