The arrival azimuths of coherent microbarom signals observed in Hawaii during 2003 are associated with high ocean wave activity the Pacific Basin, dominant wind directions troposphere, stratosphere, and mesosphere, thermal structure atmosphere. Some seasonal trends observations can be explained by winds stratosphere lower while some daily variability troposphere stratosphere. However, energy from powerful swells may overcome wind‐carried arrive to station through thermospheric ducting. Our...

More than 100 separate incidents of interactions between aircraft and volcanic ash were documented 1973 2003. Incidents on international flight paths over remote areas have resulted in engine failures significant damage expense to commercial airlines. To protect from ash, pilots need rapid reliable notification ash‐ generating events. A global infrasound array network, consisting the International Monitoring System (IMS) other national networks, has demonstrated a capability for detection...

Infrasonic array data collected at Kīlauea Volcano, Hawai'i, during November 12–21, 2002 indicate that the active vents and lava tube system near Pu'u 'Ō'ō vent complex emit almost continuous infrasound in 0.3–10 Hz frequency band. The spectral content of these infrasonic signals matches well synchronous seismic tremor. In sites protected from wind noise, significant signal to noise ratios were recorded as far ∼13 km crater 'Ō'ō. recordings suggest one or more tremor sources may be close...

Microbaroms are infrasonic waves generated by nonlinear interactions of ocean surface traveling in nearly opposite directions with similar frequencies. Such commonly occur between ∼10 s periods, which abundant the open oceans and correspond to observed 0.2 Hz spectral peak. Microbarom observations from Hawai'i during 2002–2003 show a relationship storm wave activity Pacific. Seasonal patterns microbarom arrival azimuths affected size distribution swells, dominant wind atmosphere, topographic...

Comparison of ocean buoy measurements with infrasonic array data collected during the epic winter 2002–2003 shows a clear relationship between breaking wave height and signal levels. In addition, arrays allow identification distinct zones along shoreline. Our observations suggest that can be used in conjunction buoys to estimate heights, identify regions high action, validate surface propagation models.

Developed by the infrasound group at National Center of Physical Acoustics, University Mississippi, and a few collaborators, NCPAprop is an open source software package aiming providing comprehensive set tested validated numerical models for simulating long range propagation infrasonic signals through earth's atmosphere. The algorithms implemented in are designed frequencies large enough that effects buoyancy can be neglected small to ranges hundreds thousands kilometers possible without...

Infrasound arrays in the Pacific and Indian oceans that are part of International Monitoring System (IMS) Comprehensive Nuclear Test Ban Treaty (CTBT) recorded distinct signatures associated with 26 December 2004 Sumatra earthquake ( M /9, http://earthquake.usgs.gov/) tsunami. Although radiation infrasound from large continental earthquakes is established [e.g., Le Pichon et al ., 2003], results presented present article indicate islands undergoing significant surface displacements submarine...

Infrasound signals in the microbarom band (about 0.2 Hz) generated by hurricanes often do not appear to originate near eye where winds are strongest. This paper suggests that conditions conducive (and microseism) generation can occur along trailing periphery of storm through interaction storm‐generated wavefield with ambient swell field, resulting detection bearings vary from center up 20 degrees. data Typhoon Usagi (2007) is presented supports this theory.

A terrain capable parabolic equation (PE) propagation algorithm for long range infrasound modeling has been implemented using Padé approximations the various operator valued functions that arise in PE algorithms. In this work, influence of winds are captured by effective sound speed approximation and is restricted to range-altitude plane. The ground topography included addition an impenetrable fluid below surface. impedance condition at handled explicitly, including both vertical radial...

Sutherland and Bass (2004) have developed a calculation of the speed sound attenuation at altitudes up to 160 km. Dispersion is included in their treatment though emphasis placed on absorption. That theory explored more detail describe dispersion thermosphere. In lower atmosphere, variations with altitude are dominated by temperature wind changes; vibrational rotational relaxation frequencies, which depend ratio frequency pressure ( f / P ), kilohertz megahertz range. As increases, mean free...

This presentation describes a method for predicting RMS wind noise levels within user-specified infrasonic frequency band (e.g., 1–10 Hz) using local topographic features. capability is especially valuable when performing site selection infrasound sensor array deployment. The based on building models measured data from known locations and the features corresponding to site. presented results correspond such relative terrain elevation vegetation height obtained publicly available sources....

The rumble of hypersonic objects tearing through the atmosphere can be routinely detected by sensitive infrasound sensors [ Brown et al ., 2002]. Meteors and reentering spacecraft are most common sources, although supersonic aircraft generate comparable signatures. This article concentrates on two exceptionally energetic events: tragic Columbia reentry 1 February 2003 (STS‐107) 23 April 2001 superbolide explosion. On 2001, a large meteor exploded at height ˜28.5 km between Hawaii California....

This study utilized seismograms from the U.S. Geological Survey seismological station near Ely, Minnesota, at which 39 delay-fired explosions Steel Minntac iron mine in Mountain Iron, were recorded. The waveforms analyzed both time and frequency domains to characterize amplitude energy levels as recorded over regional travel path. measurements then related delay-firing parameters furnished by Minntac. filtered five one-octave bands 0.5 Hz 16 Hz, peak velocities measured for P Rg / Lg...

It has been established that tornadoes emit an infrasonic signal is regularly detected in the 1 to 10 Hz band, although actual band expected be wider. The physical mechanism through which this generated not yet fully understood and subject of current research. Here we discuss some our experimental efforts, past present. During tornado seasons 2017, 2018, 2019, deployed a network infrasound sensor arrays northern Alabama, southern Tennessee, northwestern Georgia. We performed detailed...

Data recorded by several infrasound sensor arrays deployed in the southeastern United States during spring of 2018 have been analyzed a period when storm front passed through and spawned tornado touchdowns. The tornadoes ranged from EF-0 to EF-2. Accurate bearings obtained, corresponding at ranges up more than 100 km. Earlier day, convective cell triggered warning but no verified During this earlier passage, weaker signal was detected with that tracked cell. analyses reveal on systems...

NCPAProp is a command-line-driven, fully open-source software package first released in 2016 and under continuous development since then. It aims to provide comprehensive set of tested validated full-wave numerical models simulate long-range propagation infrasound through realistic atmospheres, at frequencies nominally the range 0.1-10 Hz. The currently includes two normal-mode varying complexity, parabolic equation model with option include range-dependent atmosphere orography. This...

The notion that tornadoes emit an infrasonic signal can be detected from great distances; and thus used to aid in the detection, monitoring, potential tracking of active tornadoes; has been discussed for decades. Much evidence accumulated showing acoustic radiation at least two distinct frequency bands, band a low audible band. It is believed physical mechanisms responsible emissions are different. We will focus here on emissions. Experimental do indeed reviewed current status theoretical...

Multiple infrasound arrays in the Pacific and Indian Oceans that are part of International Monitoring System (IMS) observed three distinct waveform signatures associated with December 26, 2004 Sumatra earthquake tsunami. Infrasound station Palau, Diego Garcia, Madagascar, Kenya (1) seismic arrivals (P, S surface) from earthquake, (2) T-phases, propagated along SOFAR channel ocean, coupled back to ground, (3) infrasonic either tsunami generation mechanism or motion ground above sea level. All...

Cyclonic storms over water radiate a infrasound at about 0.2 Hz. The atmospheric component of this radiation is called the microbarom peak. seismic microseism It believed that source non‐linear interaction colliding waves on ocean surface. Results from our ongoing studies mechanism will be reported. These include conjectures influence finite depth microbarom/microseism spectrum and origin produced by isolated storms.

Spatial wind-noise-reducing filter technologies are widely used in infrasound recording because wind is the primary source of noise this frequency band. While permanent arrays often make use large solid-pipe rosette spatial filters, portable or temporary must other materials, most popular which porous garden hose. undeniably effective at reducing noise, hoses have distinct frequency-dependent effects on signal amplitudes and by changing phase response microphone can deleterious bearing...

Several array signal processing methods can be used to estimate bearings-of-arrival (BOA) in the presence of multiple infrasound sources, and their effectiveness depends upon several factors including geometry, relative noise power spectra, cross-spectra. One most effective computationally efficient is Multiple Signal Classification (MUSIC). However, MUSIC's performance not only degrades with decreasing signal-to-noise ratio, as all methods, but also model deviates from assumption...