Infrasound in the middle stratosphere measured with a free‐flying acoustic array

Abstract

Infrasound recorded in the middle stratosphere suggests that the acoustic wavefield above the Earth's surface differs dramatically from the wavefield near the ground. In contrast to nearby surface stations, the balloon‐borne infrasound array detected signals from turbulence, nonlinear ocean wave interactions, building ventilation systems, and other sources that have not been identified yet. Infrasound power spectra also bore little resemblance to spectra recorded on the ground at the same time. Thus, sensors on the Earth's surface likely capture a fraction of the true diversity of acoustic waves in the atmosphere. Future studies building upon this experiment may quantify the acoustic energy flux from the surface to the upper atmosphere, extend the capability of the International Monitoring System to detect nuclear explosions, and lay the observational groundwork for a recently proposed mission to detect earthquakes on Venus using free‐flying microphones.

A Three‐Dimensional Array for the Study of Infrasound Propagation Through the Atmospheric Boundary Layer

“…Since it can be trapped in an elevated waveguide with the lower boundary between 0‐ and 60‐m altitude, the downward propagating wave is not reaching the surface microbarometers. Similar observations are presented in Bowman and Lees (, ). A high‐altitude balloon was used, where elevated acoustic waveguides are observed.…”

Acoustic and Seismic Fields of Hydraulic Jumps at Varying Froude Numbers

“…PSD estimates for all acoustic wavefields contain high‐power low‐frequency acoustic noise. This acoustic signal is classified as noise because it does not display cross‐spectral coherence (Figure ) and is likely explained by long‐period pressure fluctuations associated with wind noise and site‐specific thermal noise (e.g., Bowman & Lees, ).…”

Detecting Lightning Infrasound Using a High‐Altitude Balloon

“…A series of studies have recently taken place to explore how to fill this gap in our ability to monitor the atmospheric acoustic wavefield. These experiments have tested the use of microphones suspended underneath free‐floating balloons to record infrasound at high altitude (e.g., Bowman & Lees, , ; Bowman & Albert, ). Balloon deployments conducted as part of the NASA High‐Altitude Student Platform program described evidence of the ocean microbarom as well as other signals of unknown provenance (Bowman & Lees, ).…”