Surface waves magnitude estimation from ionospheric signature of Rayleigh waves measured by Doppler sounder and OTH radar.

Surface waves emitted after large earthquakes are known to induce atmospheric infrasonic waves detectable at ionospheric heights using a variety of techniques, such as high frequency (HF) Doppler, global positioning system (GPS), and recently over-the-horizon (OTH) radar. The HF Doppler and OTH radar are particularly sensitive to the ionospheric signature of Rayleigh waves and are used here to show ionospheric perturbations consistent with the propagation of Rayleigh waves related to 28 and 10 events, with a magnitude larger than 6.2, detected by HF Doppler and OTH radar respectively. A transfer function is introduced to convert the ionospheric measurement into the correspondent ground displacement in order to compare it with classic seismometers. The ground vertical displacement, measured at the ground by seismometers, and measured at the ionospheric altitude by HF Doppler and OTH radar, is used here to compute surface wave magnitude. The ionospheric surface wave magnitude (M siono ) proposed here introduces a new way to characterize earthquakes observing the signature of surface Rayleigh waves in the ionosphere. This work proves that ionospheric observations are useful seismological data to better cover the Earth and to explore the seismology of the Solar system bodies observing the ionosphere of other planets.

One-way approximation for the simulation of weak shock wave propagation in atmospheric flows.

A numerical scheme is developed to simulate the propagation of weak acoustic shock waves in the atmosphere with no absorption. It generalizes the method previously developed for a heterogeneous medium [Dagrau, Rénier, Marchiano, and Coulouvrat, J. Acoust. Soc. Am. 130, 20-32 (2011)] to the case of a moving medium. It is based on an approximate scalar wave equation for potential, rewritten in a moving time frame, and separated into three parts: (i) the linear wave equation in a homogeneous and quiescent medium, (ii) the effects of atmospheric winds and of density and speed of sound heterogeneities, and (iii) nonlinearities. Each effect is then solved separately by an adapted method: angular spectrum for the wave equation, finite differences for the flow and heterogeneity corrections, and analytical method in time domain for nonlinearities. To keep a one-way formulation, only forward propagating waves are kept in the angular spectrum part, while a wide-angle parabolic approximation is performed on the correction terms. The numerical process is validated in the case of guided modal propagation with a shear flow. It is then applied to the case of blast wave propagation within a boundary layer flow over a flat and rigid ground.