Papers by Daniel Bowman
Low frequency acoustic waves (infrasound) are generated by a variety of natural and anthropogenic... more Low frequency acoustic waves (infrasound) are generated by a variety of natural and anthropogenic phenomena. Although infrasound propagates throughout the atmosphere, the vast majority of acoustic studies utilize sensors on or near the Earth's surface. This paper describes results from two infrasound arrays launched into the stratosphere, one in August 2014 and the other in September 2015. The observations presented here are the first stratospheric infrasound measurements reported in scientific literature in 50 years. Acoustic signals recorded on the balloon borne sensors were different than those recorded by nearby infrasound stations on the ground. The 0.2 Hz ocean microbarom was detected in the stratosphere, but was not observed on nearby ground stations. A series of narrow band signals were also observed in the stratosphere, some of which varied in frequency over tens of minutes. The source of these signals is unclear. Wind noise decreased with altitude during the ascent, becoming negligible above 20 km. It was absent when the balloon was neutrally buoyant, although it was pervasive on ground stations operating in the same region during the day. Spectral characteristics of stratospheric infrasound were similar between the two flights and also resembled the last experiment in the early 1960s, but spatiotemporal variations in signal strength and frequency were also observed. Future efforts should focus on characterizing infrasound sensor operation in extreme environments and increasing spatial and temporal frequency of acoustic measurements in the free atmosphere. Results from this study have implications for long range detection of events such as nuclear blasts, the quantification of acoustic energy that heats the upper atmosphere, and calibration of a proposed mission to place airborne acoustic sensors on Venus.
Infrasound recorded in the middle stratosphere suggests that the acoustic wavefield above the Ear... more 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.
Seismological Research Letters, 2013
Geophysical Research Letters, 2014
ABSTRACT Infrasound and high speed imaging during a series of field-scale buried explosions sugge... more ABSTRACT Infrasound and high speed imaging during a series of field-scale buried explosions suggest new details about the generation and radiation patterns of acoustic waves from volcanic eruptions. We recorded infrasound and high speed video from a series of subsurface explosions with differing burial depths and charge sizes. Joint observations and modeling allow the extraction of acoustic energy related to the magnitude of initial ground deformation, the contribution of gas breakout, and the timing of the fallback of displaced material. The existence and relative acoustic amplitudes of these three phases depended on the size and depth of the explosion. The results motivate a conceptual model that relates successive contributions from ground acceleration, gas breakout, and spall fallback to the acoustic amplitude and waveform characteristics of buried explosions. We place the literature on infrasound signals at Santiaguito volcano, Guatemala, and Sakurajima and Suwonosejima volcanoes, Japan, in the context of this model.
The National Oceanic and Atmospheric Administration Operational Model Archive and Distribution Sy... more The National Oceanic and Atmospheric Administration Operational Model Archive and Distribution System (NOMADS) facilitates rapid delivery of real time and archived atmospheric and oceanic model outputs from multiple agencies. These data are free to the scientific community, industry, and the public. The rNOMADS package provides an interface between NOMADS and the R programming language. Like R itself, rNOMADS is open source and cross platform. It utilizes server-side functionality on the NOMADS system to subset model outputs for delivery to client R users. We discuss rNOMADS implementation and usage as well as provide two case studies. Users can download rNOMADS from within the R interpreter or from the Comprehensive R Archive Network (CRAN).
Thesis Chapters by Daniel Bowman
Daniel Charles Bowman: Infrasound from Ground to Space (Under the direction of Jonathan M. Lees)
Drafts by Daniel Bowman
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Papers by Daniel Bowman
Thesis Chapters by Daniel Bowman
Drafts by Daniel Bowman