Natural Infrasound as an Atmospheric Probe

Abstract

For four years continuous recording of infrasonic signals in the frequency range 0.1 to 1 Hz, known as microbaroms, has been conducted at Palisades, New York. The microbaroms we recorded are radiated into the atmosphere by interfering ocean waves in the North Atlantic as far as 2000 km away. A characteristic diurnal variation in the amplitude of the received signal has been noted, independent of any variation in the source. We conclude that the variation is due to variations of the factors affecting atmospheric sound propagation, namely wind and temperature.In winter a semidiurnal variation in signal amplitude is observed, with maximum reception around 11 : 00 and 22 : 00 local time. Reference to wind and temperature observations in the literature shows that at these times the lowest level of reflection of the vertically propagating signal occurs between 100 and llOkm due to the presence of strong east winds. At 18 : 00, time of minimum amplitudes, the reflection level rises to about 115 km because of a change in tidal wind phase. Viscous dissipation associated with the changed reflection height can account for the observed signal weakening. A third maximum, a less regular effect, is found to be related to more variable winds between 95 and 105 km.In summer, reflection is found to occur from about 50 km due to the presence of stratospheric easterlies. The summer diurnal variation, different from that of the winter, exhibits only a weak minimum about 20 : 00. This appears to result from a diurnal temperature variation superimposed on a diurnal wind variation. Abnormally high microbaroms were recorded at times that can be related to an atmospheric event known as a stratospheric warming. Microbaroms thus provide a continuously available natural mechanism for probing the upper atmosphere. We conclude that the establishment of microbarom observation systems could give a comprehensive technique for monitoring several upper atmospheric parameters.

An overview of volcano infrasound: From hawaiian to plinian, local to global

“…Assink et al, 2012) and stratosphere (e.g. Donn and Rind, 1971) cause minor, but observable variations in infrasound propagation and signal characteristics.…”

Analysis of Signals from an Unique Ground-Truth Infrasound Source Observed at IMS Station IS26 in Southern Germany

“…These propagation models in turn have to be used to infer the strength of any detected infrasound source for any CTBT-related infrasound monitoring activity. For this reason it is highly desirable during the establishment of such infrasound propagation models to use calibration sources which are greatly repeatable during any atmospheric conditions (DONN and RIND, 1971;GAR-CES et al, 1998;DROB et al, 2003;LE PICHON and DROB, 2004).…”

Toward an Improved Representation of Middle Atmospheric Dynamics Thanks to the ARISE Project

“…During a SSW, changes in the stratospheric wind and temperature substantially influence the infrasound atmospheric waveguide, which is detectable in the infrasound observations at the ground (e.g., Donn and Rind 1971;Evers and Siegmund 2009;Hedlin and Drob 2014;Assink et al 2014a). Variations range from minor, for example, small bearing variations, to dramatic, i.e., no longer detecting a signal in a specific direction.…”

“…They are strongly affected by the stratospheric winds variability and fluctuations from GWs in the wind profiles (Le Pichon et al 2008;Kulichkov et al 2010). It was suggested in the pioneering work of Donn and Rind (1971), Rind et al (1973) and Rind and Donn (1975) that infrasound from well-identified repetitive sources could be used for remote determination of the upper-atmosphere wind speeds. IMS stations, quasi-continuously detecting infrasound from volcanoes, are well-adapted to these studies.…”