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Research
Infrasound publications
A climatology of infrasound detections in Northern Norway at the experimental ARCI array
L.G. Evers and J. Schweitzer Abstract The study of infrasound is experiencing a renaissance in recent years since it was chosen as a verification technique for the Comprehensive Nuclear-Test-Ban Treaty. Currently, 60 infrasound arrays are being installed to monitor the atmosphere for nuclear tests as part of the International Monitoring System (IMS). The number of non-IMS arrays also increases world wide. The experimental ARCES infrasound array (ARCI) is an example of such an initiative. The detectability of infrasound differs for each array and is a function of the array location and configuration, the state of the atmosphere and the presence of natural and anthropogenic sources. In this study, a year of infrasound data is analyzed as recorded by ARCI. Contributions of the atmosphere and the sources are evaluated in both a low (0.1-1.0 Hz) and high frequency (1.0-7.0 Hz) pass-band. The enormous number of detections in the low frequency band is explained in terms of the stratospheric wind and ocean wave activity and compared with the detection of microseism. Understanding the detectability in the low frequency band is of utmost importance for successfully applying infrasound as a verification technique since small-sized nuclear test will show up in this frequency range.
Results from the array processing of ARCI data in the low frequency band from 0.1 to 1.0 Hz. The lower frame shows the Fisher ratios as function of time, that is, between 2008, March 13 and 2009, May 14. The Fisher ratio is related to the signal-to-noise (SNR) power ratio on the traces (see the axis on the right). The top frames gives the resolved apparent sound speed and backazimuth. Color coded are the number events per hour with a SNR larger than one. Five or more events are indicated by red colors. The black dots represent the wind direction at 50 km altitude from the ECMWF analysis at 69.50N, 25.50E. The equinoxes are indicated by the vertical dashed lines.
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