Modeling of acoustic and gravity waves propagation through the atmosphere with spectral element method

Wednesday, 17 December 2014
Raphael Garcia1, Quentin Brissaud1, Roland Martin2 and Dimitri Komatitsch3, (1)Institut Supérieur de l'Aéronautique et de l'Espace, SSPA/DEOS, Toulouse Cedex 04, France, (2)géosciences environnement toulouse, Toulouse, France, (3)CNRS/University of Aix-Marseille, Laboratory of Mechanics and Acoustics, Marseille, France
Low-frequency events such as tsunamis generate acoustic and gravity waves which quickly propagate in the atmosphere. Since the atmospheric density decreases exponentially as the altitude increases and from the conservation of the kinetic energy, those waves see their amplitude raise (to the order of $10^5$ at 200km of altitude), allowing their detection in the upper atmosphere.

Various tools have been developed through years to model this propagation, such as normal modes modeling or to a greater extent time-reversal techniques, but none offer a low-frequency multi-dimensional atmospheric wave modelling.
A modeling tool is worthy interest since there are many different phenomena, from quakes to atmospheric explosions, able to propagate acoustic and gravity waves.

In order to provide a fine modeling of the precise observations of these waves by GOCE satellite data, we developed a new numerical modeling tool.
Starting from the SPECFEM program that already propagate waves in solid, porous or fluid media using a spectral element method, this work offers a tool with the ability to model acoustic and gravity waves propagation in a stratified attenuating atmosphere with a bottom forcing or an atmospheric source.
Atmospheric attenuation is required in a proper modeling framework since it has a crucial impact on acoustic wave propagation. Indeed, it plays the role of a frequency filter that damps high-frequency signals.
The bottom forcing feature has been implemented due to its ability to easily model the coupling with the Earth's or ocean's surface (that vibrates when a surface wave go through it) but also huge atmospheric events.