A comparison of infrasound signals refracted from stratospheric and thermospheric altitudes

Abstract

[1] Over the last several years, a large number of ground-based infrasound arrays have been established for explosion monitoring as part of the International Monitoring System of the Comprehensive Nuclear Test Ban Treaty Organization. Results from these arrays have become valuable in understanding long-range infrasound propagation in the atmosphere and complement earlier data. Two types of signals are often observed for a given source: those refracted at stratospheric heights and at thermospheric heights. In this contribution we compare several characteristics of these two signal types including observed pressure amplitude, average travel velocity, bearing, and signal duration. For this study we use archival data from atmospheric nuclear explosions, high explosive chemical explosions on the surface, earthquakes with previously detected stratospheric signals, and earthquakes for which stratospheric signals were not detected. We show that the combination of stratospheric and thermospheric signals may provide independent estimates of wind propagation conditions and source characteristics. The observations of both signal types may increase the confidence level of an infrasound signal detection.

The European Arctic: A Laboratory for Seismoacoustic Studies

“…with generally higher apparent velocities (angles of incidence). These properties are consistent with thermospheric phases (Whitaker and Mutschlecner, 2008) and the differing apparent velocities for these later phases indicate returns from different altitudes. It is noted that short duration infrasound was detected at IS37 for all 3 of the final low-yield explosions.…”

“…The low celerity, lower frequency signal, and greater angle of incidence are indicative of thermospheric phases (e.g. Mutschlecner and Whitaker, 1999;Whitaker and Mutschlecner, 2008). Given that the effective velocity in the thermosphere always exceeds the effective velocity at ground-level, thermospheric phases are always predicted.…”

Incorporating numerical modeling into estimates of the detection capability of the IMS infrasound network

“…One dominant factor influencing infrasound detection is the seasonal oscillation of the dominant east‐west (zonal) component of the stratospheric wind flow [e.g., Balachandran et al , 1971]. This oscillation, clearly captured in climatological wind models [e.g., Drob et al , 2003], controls to first order where infrasound signals are expected to be detected since detection capability is preferable downwind [e.g., Whitaker and Mutschlecner , 2008]. Using state‐of‐the‐art specifications of the stratospheric winds and time‐dependent station noise models, recent simulations predicted that explosions equivalent to ∼500 t of TNT would be detected by at least two stations at any time of the year over the earth's surface [ Le Pichon et al , 2009].…”

“…Although most of the detected signals in the frequency band of interest propagate in a stratospheric waveguide, thermospheric arrivals may be recorded upwind of the source. Models predicting attenuation relations of all observed arrivals, such as those proposed by Whitaker and Mutschlecner [2008] would provide more realistic detection levels for local tropospheric ducts and long propagation range scenarios for stratospheric and thermospheric arrivals.…”

The Development of Global Probabilistic Propagation Look-Up Tables for Infrasound Celerity and Back-Azimuth Deviation

“…To compare the model results with the observed data, we analyzed celerity distributions as a function of range for azimuths in the western quadrant relative to the source (225°-315°, defined by Marcillo et al, 2014 andNippress et al, 2014), in which the majority of the arrivals occur due to the stratospheric winds blowing east-to-west during summer months (e.g., Balachandran et al, 1971;Whitaker and Mutschlecner, 2008;Hedlin and Walker, 2013;Nippress et al, 2014). For both model and data distributions, we group celerity observations at the corresponding azimuths into range bins spanning 50 km and ranging from 0 to 1000 km from the source.…”