Bruno Ribstein

Séminaire régulier
LRC Méso - CMLA - ENS Paris Saclay

The work present a model for the infrasounds emitted by 10 tonnes equivalent TNT and measured 320km away in Hukkakero observatory station (Norway). Low frequency acoustic-gravity waves (infrasounds) are generally produced and used to remotely detect strong explosions as early signals of potential tsunamis, using their possibility of long-distance and coherent propagation. Part of the upward propagation of a wave-packet is reflected at critical levels of the effective sound speed. Modeling the propagation of infrasound therefore highly depend on knowing precisely the altitude of those critical levels, and so on the existence of subgrid-scale internal waves. No matter how important internal waves can be, they are still yet not resolved by numerical weather prediction models, and so need to be parameterized. We here use a stochastic parameterization to simulate those internal waves from the state of the atmosphere predicted by ECMWF, and then use them to compute the propagation of the infrasound. A version previously tuned by co-authors for climate modeling purpose is shown to not retrieve the signal observe, as the version lack in small-scale wave
in the middle atmosphere. A new version of the wave-parameterization is here proposed which accurately allow the modeling of infrasound propagation. Values of the internal wave drag obtained using the new parameterization are in agreement when compared with observation.