The Role of Atmospheric Uncertainties on Long Range Propagation of Infrasounds

Abstract

The normal mode method provides a reduced basis that can decribe the long range propagation of infrasounds in the atmosphere. Using that technique, we study the infrasound signal recorded in Japan after the explosion of the first reactor of the Fukushima power plant. By applying small perturbations to the sound speed profile, we find highly sensitive structures that can radically impact the signal. Moreover, the main tendencies seem to change when considering different datasets for the meteorological profiles.

Range-dependent propagation modeling of infrasound in complex atmospheres

“…First we show that the results of our code agree with those obtained by Bertin et al 1 when the sound speed only weakly depends on r. Next, we assess the effect of topography and streamwise atmospheric variations on the ground signals.…”

“…We refer the reader to the article by Candelier et al 9, 10 for more details on this code. Interestingly, Bertin et al 1 showed that very close velocity profiles c(z) could lead to distinct arrivals. However, since the real profile is non-homogeneous from the source to the station, his results also suggest that horizontal variations of the wind must be considered when modeling the long-range propagation of impulsive sound.…”

“…In a previous work, Bertin et al 1 investigated the sensitivity of the signal recorded at I30JP as a function of variations in the effective sound speed. The authors used a normal mode approach with a pseudo-spectral code where they made the assumption that the atmospheric state only depends on the altitude.…”

“…To begin with, we compare the FEM to the normal mode approach used by Bertin et al 1 In their work, Bertin et al 1 assumed that the atmosphere was invariant along r so that only the vertical gradients were considered. So we start by considering the four profiles c(z) depicted in figure 2, obtained from the ERA-40 and 91-level data taken above the source and the station.…”

“…Using these data, recent studies (Bertin et al 1 ) showed that ray tracing-based methods are not able to return the proper effect of atmospheric variability on the signals. This is a well known problem which makes the simulation of recorded signals challenging.…”