Observational Evidence for Wind-Driven Low-Pass Filtering of Infrasound at Short Range

TL;DR

This study provides direct observational evidence that tropospheric winds can cause azimuth-dependent low-pass filtering of infrasound at short ranges, significantly affecting wave spectral characteristics even within a few kilometers.

Contribution

It demonstrates that atmospheric winds can impose azimuth-dependent low-pass filtering on infrasound, independent of temperature inversions, based on controlled explosion observations.

Findings

Wind-driven low-pass filtering varies with azimuth.

Upwind paths show longer periods due to filtering.

Downwind paths preserve original wave characteristics.

Abstract

Infrasound from controlled explosions provide a unique opportunity to isolate atmospheric effects on propagation. We report observations from two campaigns in May and October 2024, each featuring 10-ton TNT-equivalent controlled surface chemical explosions recorded by a dense network of 31 single-sensor stations within 23 km. Despite identical sources, the observed wavefields were very different. October signals followed a near-unimodal period-distance trend, whereas May signals exhibited a pronounced azimuthal bifurcation in both period and celerity. Downwind paths largely preserved the short-period baseline observed in October, while upwind paths showed systematically longer periods caused by wind-driven low-pass filtering. This study provides the first direct observational evidence that tropospheric winds can impose azimuth-dependent low-pass filtering at local ranges, without the influence of measured temperature inversions. Thus, the structure of the atmosphere can modify the spectral characteristics of low-frequency acoustic waves even at a distance of only a few kilometers.