Multi-Arrival Infrasound from Meteoroids: Fragmentation Signatures versus Propagation Effects in a Fine-Scale Layered Atmosphere

Infrasonic signatures of meteoroid fragmentation are frequently ambiguous: do multiple arrivals signify a complex breakup or merely the distorting effects of a layered atmosphere? Resolving this ambiguity is critical for accurate energy estimates and source reconstruction. In this study, we address this challenge by analyzing a unique regional dataset of well-constrained meteoroid events observed by the Southern Ontario Meteor Network and the co-located Elginfield Infrasound Array. We employ pseudo-differential parabolic equation (PPE) simulations to quantify how fine-scale gravity-wave structures in the stratosphere and lower thermosphere modify acoustic waveforms at ranges <300 km. Our modeling reveals that while fine-scale layering can stretch signals and generate diffuse oscillatory tails, it does not produce discrete, high-amplitude pulse splitting at ranges below ~140 km. By applying these results to the rare multi-arrival event 20060305, we demonstrate that its distinct double arrival at 100 km range is inconsistent with atmospheric multipathing and provides definitive evidence of separate fragmentation episodes. These findings establish new diagnostic criteria for separating source physics from propagation artifacts, improving the reliability of infrasound as a monitoring tool for natural bolides, space debris re-entries, and catastrophic launch failures.

💡 Research Summary

The paper tackles a long‑standing ambiguity in regional infrasound observations of meteoroids: when multiple arrivals are recorded at a single station, are they signatures of distinct fragmentation events along the meteoroid trajectory, or are they artifacts produced by propagation through a finely layered atmosphere? To answer this, the authors exploit a unique dataset from the Southern Ontario Meteor Network (SONM) and the co‑located Elginfield Infrasound Array (ELFO), which together provide calibrated optical trajectories, synchronized infrasound waveforms, and atmospheric profiles for 71 meteoroid events recorded between 2006 and 2011. While most events show a single coherent arrival, 16 exhibit two or more arrivals; only one of these, the 20060305 event, presents two well‑resolved, high‑signal‑to‑noise arrivals with consistent back‑azimuth and celerity, making it an ideal case study.

The methodological core is a pseudo‑differential parabolic equation (PPE) propagation model that incorporates realistic fine‑scale (FS) atmospheric structure generated by internal gravity waves (IGWs). The effective sound speed, C_eff(z,r)=c_ad(z)+u·n̂, combines the adiabatic sound speed with wind projection along the source‑receiver line. A background profile derived from the Ground‑to‑Space (G2S) climatology supplies large‑scale temperature and wind fields up to ~120 km. Superimposed on this are IGW‑based perturbations ΔC_eff(z,r) with vertical and horizontal wavelength spectra matching measurements from MST radars and satellite data. These perturbations are introduced at 28 km horizontal steps, creating a two‑dimensional effective sound‑speed field that reproduces the scattering, refraction, ducting, and shadow‑zone formation observed in the real atmosphere.

Simulation results reveal that FS layering can stretch a signal, generate low‑frequency oscillatory tails, and even allow weak energy to leak into geometric shadow zones via diffraction and anti‑guiding. However, crucially, at ranges below ~140 km the FS‑induced multipath does not produce discrete, high‑amplitude pulse splitting; instead it yields a continuous, distorted waveform. Only at greater distances does the model generate clearly separated pulses.

Applying this framework to the 20060305 event, the authors find that the observed double arrival at ~100 km range, with a ~2 s separation and comparable amplitudes, cannot be reproduced by any realistic FS atmospheric configuration. The timing, amplitude ratio, and spectral content match the signature expected from two independent fragmentation sources rather than from atmospheric multipathing. Consequently, the event provides definitive evidence of genuine multi‑fragmentation.

From these findings the authors propose practical diagnostic criteria for future analyses: (1) at ranges ≤140 km, arrival separations ≤1 s are likely atmospheric; separations >1 s, especially with similar or larger secondary amplitudes, indicate fragmentation; (2) the presence of distinct dominant periods in each arrival supports a source‑origin interpretation; (3) the relative altitude of the fragmentation point to the FS layers determines whether a “thermospheric reflection” or a direct arrival is expected, offering additional constraints for energy deposition estimates.

The study’s implications are significant. By establishing a robust method to separate source physics from propagation artifacts, it enhances the reliability of infrasound for quantifying kinetic energy, reconstructing fragmentation histories, and monitoring hazardous atmospheric entry events such as natural bolides, space‑debris re‑entries, and catastrophic launch failures. The diagnostic framework can be readily integrated into existing global infrasound networks, improving both scientific understanding and planetary defense capabilities.