Infrasound monitoring of volcanoes to probe high-altitude winds

International audience; Active volcanoes in the Vanuatu archipelago permanently generate infrasonic waves. Their monitoring over 1 year exhibits clear seasonal trends in the direction of arrival of the detected signals. From summer to winter the azimuth variation reaches 15°. This deviation is essentially due to the reversibility of the zonal stratospheric wind with season which strongly affects the deflection of the ray direction. A three-dimensional (3-D) ray-tracing modeling roughly explains the observed seasonal trend in the azimuth variation but underestimates its amplitude. The discrepancy between the measurements and the results of simulation is explained by undervalued wind speeds in the upper atmosphere. Infrasonic observations are used as input of an inversion scheme for adjusting the vertical structure of the wind in the upper stratosphere and mesosphere. It is shown that the mesospheric zonal winds are underestimated by at least 20 m/s throughout the year with differences reaching 50 m/s.