Estimating tropospheric and stratospheric winds using infrasound from explosions

Abstract

The receiver-to-source backazimuth of atmospheric infrasound signals is biased when cross-winds are present along the propagation path. Infrasound from 598 surface explosions from over 30 years in northern Finland is measured with high spatial resolution on an array 178 km almost due North. The array is situated in the classical shadow-zone distance from the explosions. However, strong infrasound is almost always observed, which is most plausibly due to partial reflections from stratospheric altitudes. The most probable propagation paths are subject to both tropospheric and stratospheric cross-winds, and our wave-propagation modelling yields good correspondence between the observed backazimuth deviation and cross-winds from the ERA-Interim reanalysis product.We demonstrate that atmospheric cross-winds can be estimated directly from infrasound data using propagation time and backazimuth deviation observations. We find these cross-wind estimates to be in good agreement with the ERA-Interim reanalysis.

Assimilation of atmospheric infrasound data to constrain tropospheric and stratospheric winds

“…The position r a of the wavefront depends on the infrasound speed of propagation along d a , which is the sum of the sound speed (a function mainly of temperature) and the actual background wind along the direction of the propagation w a (r a , t). Blixt et al (2019) define an average cross-wind as:…”

“…The wave travels both in the r a and z directions. The wave travels in the vertical to a given maximum altitude from where it returns down to ground (e.g., due to partial reflection as explained in Blixt et al, 2019) and it is then detected at the receiver. As in the 2D case, the wave travels through a cross-wind field which leads to F I G U R E 2 Depiction of an infrasound wave (yellow) travelling through an atmospheric volume.…”

“…The current study follows directly from a recent paper by Blixt et al (2019), which used the same dataset to demonstrate that atmospheric cross-winds can be estimated directly from infrasound data using propagation time and back-azimuth deviation observations, and interpreted these results in the context of ERA-Interim reanalysis winds. There is a physical effect which is the basis of this work: when a steady cross-wind acts on a propagating acoustical plane wave, a bending of the wavefront is introduced.…”

“…We use this physical effect to assess the dynamical evolution of the stratosphere during several events, as sampled by the infrasound waves on their paths between Finland and a ground-based station in Northern Norway. The array signal processing algorithms exploit infrasound signals recorded on a set of 25 sensors distributed on the ground within a 3 km wide aperture (figure 1 of Blixt et al, 2019).…”

Global Monitoring and Characterization of Infrasound Signatures by Large Fireballs

“…Infrasound, which is low-frequency sound below the threshold of human hearing (around [16][17][18][19][20], is generated by a large number of natural and anthropogenic phenomena [1,2]. While the monitoring and verification of man-made atmospheric explosions using infrasound array recordings is one of the main purposes of the infrasound observation technology [3][4][5], also the detection of natural explosions or shock waves, such as generated by large fireballs during meteoroid or asteroid entries into the Earth's atmosphere, is a major topic of interest with respect to infrasound [6][7][8].…”