Infrasound and the Dynamical Stratosphere: A new application for operational weather and climate prediction

Infrasound is low-frequency inaudible sound (< 20Hz), used as a waveform verification technique for the Comprehensive Nuclear-Test-Ban Treaty (CTBT). In this thesis, it is shown that infrasound can provide useful additional upper atmospheric observations in a region where data coverage is sparse; beyond the middle stratosphere direct information of wind is missing in current numerical weather prediction models. Passive ambient infrasound signals can act as an atmospheric probe. Observed and simulated infrasound wavefront parameters are compared, i.e., back azimuth, apparent velocity, or travel time. Wavefront parameters are extracted from the continuous waveform recordings using signal detectors and array processing techniques and simulated by ray theory using various atmospheric conditions. The theoretical basis of this method relies on the assertion that sound propagates through a particular atmospheric state. The state that is closest to reality will then lead to simulated values that are closest to the observed values. It is demonstrated that infrasound has the potential to contribute to operational weather prediction applications by validation of atmospheric analysis and forecast products, in particular in regions above 30 km altitude. In addition, knowledge of the dynamical stratosphere is utilized for infrasound monitoring, in order to benefit CTBT verification efforts.