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Active volcanoes are significant sources of infrasound in the 1–4‐Hz frequency band and are detectable at ranges of hundreds of kilometers. The propagation is affected by the atmospheric temperature, wind, and attenuation profiles, which are range and time dependent. In this paper, a 3‐D atmospheric parabolic equation method that accurately incorporates the effects of wind is applied to modeling volcanic infrasound propagation. A parabolic equation is derived using a narrow angle operator approximation in azimuth and a wide angle approximation in depth to account for wind‐induced refraction that can trap or disperse sound energy, leading to large variations of propagation with wind conditions. The atmospheric specification for this model is derived from the attenuation coefficients of Sutherland and Bass [J. Acoust. Soc. Am. 115, 1012–1032 (2004)] and the temperature/wind profiles from the Naval Research Laboratory Ground to Space model [J. Geophys. Res. 108, 4680–4691 (2003)], which provides global atmospheric profiles from the ground to 200 km altitude updated four times daily. Signal amplitude and direction of arrival estimates from the model are compared with measurements of volcanic infrasound at listening stations several hundred kilometers from the source. [Work supported by ONR.]

We investigate the prospects for utilizing infrasound signals from geophysical sources to improve our knowledge of upper atmospheric winds and temperatures. We present results from numerical experiments designed to quantify the statistical performance of an idealized infrasonic upper atmospheric remote sensing network over a range of propagation modeling assumptions, source types, and geophysical variables. For a series of hypothetical events, infrasonic observables are calculated with a spherical 3‐D ray tracer and series of atmospheric profiles spanning the range of geophysical parameters. These synthetic measurements are then inverted to estimate the original atmospheric background fields. A nonlinear least‐squares estimation procedure that accounts for uncertainties in both the dependent and independent variables is used. The retrieved atmospheric profiles are represented by a set of truncated empirical orthogonal functions to incorporate a priori knowledge of atmospheric structure and reduce the number of parameters. Our numerical experiments indicate that it is indeed possible to make meaningful estimates of upper atmospheric environmental profiles with today’s infrasound networks. [Work supported by the Office Naval Research.]

Infrasound originating from volcanic sources in the 1–4 Hz range is detectable at long ranges by remote monitoring stations. The effects of wind, in addition to the atmospheric sound speed, is non‐negligible for the propagation of these signals. Recent developments in parabolic equation (PE) methods are applicable to infrasonic propagation where both wide‐angles and high‐Mach number atmospheric flows are important. We apply this model to infrasonic data measured from volcanoes in the Archipelago of Vanuatu in Oceania (e.g., LePichon et al., 2005), as well as other potentially active volcanoes. The diurnal variations and seasonal variations in measured pressure amplitudes are modeled in the context of recent multi‐year observations of volcanic infrasound. The significance of upper atmospheric tidal amplitudes, range dependence, and prevailing gravity waves structure in these calculations are also considered. [Work supported by ONR.]

Infrasound arrays in the Pacific and Indian oceans that are part of the International Monitoring System (IMS) of the Comprehensive Nuclear Test Ban Treaty (CTBT) recorded distinct signatures associated with the 26 December 2004 Sumatra earthquake (M/9, http://earthquake.usgs.gov/) and tsunami. Although the radiation of infrasound from large continental earthquakes is established [e.g., Le Pichon et al., 2003], the results presented in the present article indicate that islands undergoing significant surface displacements from submarine earthquakes can produce infrasound. Far more intriguing is the possibility that the initiation and propagation of a tsunami may produce low-frequency sound near the source as well as along coastlines and basins. Since distant sound effectively propagates at ˜300 m/s and tsunamis propagate at ˜200 m/s, precursory sound could potentially be used as a discriminant for tsunami genesis.

[1] The Sun's Bastille Day flare on July 14, 2000 produced a variety of geoeffective events. This solar eruption consisted of an X-class flare followed by a coronal mass ejection that produced a major geomagnetic storm. We have undertaken a study of this event beginning with an analysis of the effects of the radiative phase of the flare on the dayglow and the ionosphere. The key new enabling work is a novel method of evaluating the X-ray and extreme ultraviolet (EUV) solar spectral irradiance changes associated with the flare. We find that the solar radiative output enhancements modeled during the flare are consistent with measurements of both solar EUV irradiance and far UV Earth thermospheric dayglow. We use the SAMI2 model to predict global ionospheric changes along a magnetic meridian that show significantly different northern and southern effects, suggesting that flares can be used to study ionospheric dynamics.

Temporally varying atmospheric temperature and wind velocity data from ground level up to heights of 250 km are used to compute travel time curves and azimuth deviations for acoustic waves propagating over the CTBT infrasonic array sites of Hawaii and Alaska. An enhanced formulation of the tau‐p method [Garces et al., Geophys. J. Int. (1998)] permits theoretical estimates of travel times and azimuth deviations for infrasonic waves traveling through a stratified, windy atmosphere. Atmospheric data for the season of Winter is obtained from the Naval Research Laboratory MSISE‐90 and HWM‐93 models, which include tidal and geomagnetic effects. These data will be supplemented with ground‐based and satellite‐based atmospheric data. An ensemble of circumstances, encompassing infrasonic wave propagation through anomalous environmental conditions as well as studies on site‐specific effects, will be presented. Based on the predicted phases, effective detection and source inversion algorithms will be developed at each array.

International audience; On September 15th, 2007, around 11:45 local time in Peru, near the Bolivian border, the atmospheric entry of a meteoroid produced bright lights in the sky and intense detonations. Soon after, a crater was discovered south of Lake Titicaca. These events have been detected by the Bolivian seismic network and two infrasound arrays operating for the Comprehensive Nuclear-Test-Ban Treaty Organization, situated at about 80 and 1620 km from the crater. The localization and origin time computed with the seismic records are consistent with the reported impact. The entry elevation and azimuthal angles of the trajectory are estimated from the observed signal time sequences and back-azimuths. From the crater diameter and the airwave amplitudes, the kinetic energy, mass and explosive energy are calculated. Using the estimated velocity of the meteoroid and similarity criteria between orbital elements, an association with possible parent asteroids is attempted. The favorable setting of this event provides a unique opportunity to evaluate physical and kinematic parameters of the object that generated the first actual terrestrial meteorite impact seismically recorded.

The similarity transformation (ST) defines a new class of robust and stable parametric functions with embedded physical shape information to optimize flexibility in fitting or inverting data. The similarity transformation also permits the extraction of information on the shape of a particular class of physical functions, thereby providing the basis for comparing alternative models and for analyzing the information content of data. We employ these properties of similarity transformations to study differences between state-of-the-art physics-based atmospheric models (the thermosphere ionosphere electrodynamic general circulation model, or TIEGCM) and empirical atmospheric models (Mass Spectrometer Incoherent Scatter, or MSIS) and to investigate the universality of these models; we examine the role of noise in determining acceptable resolution for faithful retrieval of physical properties; and we measure the performance of MSIS-based forward models for inversion of ultraviolet remote sensing of the neutral upper atmosphere. The similarity transform method proves to be a valuable new tool for identifying common and discrepant properties of the models. Further, the ST method shows that TIEGCM and MSISE-90 profiles embody similar shape information and that a suitable ST parameterization can be constructed that approximates profiles from either model to within a few percent accuracy.