Internal gravity waves in the middle atmosphere and their impact on infrasound propagation across the International Monitoring System

Infrasound technology is used to monitor atmospheric events in order to guarantee compliance with the Comprehensive Nuclear-Test-Ban Treaty (CTBT). Over the 60 infrasound stations initially planned, 53 are operational to date as part of the International Monitoring System (IMS). As opposed to the waveform-related technologies that are used by the IMS to monitor the two other media of the geosphere (the underground and the oceans), infrasound waves are travelling in a continuously varying propagation medium. From minutes to hours and from a few hundreds of meters in the vertical to thousands of kilometers in the horizontal, atmospheric perturbations affect detection capabilities of the IMS at various scales. These perturbations need to be taken into account, for infrasound analysis to be able to provide accurate localization and characterization of sources of interest. In particular, internal gravity waves (atmospheric buoyancy waves) pose a serious challenge to atmospheric modelling because of the unresolved involved processes. They can dramatically affect transmission losses across the globe. Through numerical experiments and using high resolution modelling outputs of the atmosphere, backed up by atmospheric measurements, we demonstrate how gravity waves impact infrasound attenuation and drive signal amplification across the IMS.