Influence of atmospheric structure and topography on infrasonic wave propagation

• Published in: Journal of geophysical research. Solid earth Vol. 119; no. 4; pp. 2988 - 3005
• Main Authors: Lacanna, G., Ichihara, M., Iwakuni, M., Takeo, M., Iguchi, M., Ripepe, M.
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01-04-2014
• Subjects: Amplitudes; Atmosphere; Atmospheric data; Atmospheric models; atmospheric property; Atmospheric structure; Atmospherics; Computer simulation; Data; FDDI modeling; Finite difference time domain method; Geophysics; Gravity; Infrasonic waves; Infrasonics; Infrasound; Mathematical models; Modelling; monitoring; Numerical simulations; Propagation; Sound diffraction; Topographic effects; Topography; Volcanic activity; volcano; Volcanoes; Wave diffraction; Wave propagation; Wave refraction; Waveforms; Wind speed
• ISSN: 2169-9313; 2169-9356
• DOI: 10.1002/2013JB010827

The effects of topography and atmospheric structures on infrasonic wave propagation from a volcanic source were investigated using observations and numerical modeling. This paper presents the first long‐term observational data set showing spatiotemporal variations in patterns of infrasound propagation at distances of up to 60 km from a persistently active infrasound source (Sakurajima Volcano, Japan). The data show that the amplitudes of infrasonic waves received at distant stations relative to those received at a reference station close to the source can vary up to an order of magnitude over short time intervals and short distances and that they do not follow the theoretical geometric decay expected for homogeneous media. Moreover, waveforms also change significantly in both time and space. Numerical simulations were performed using a two‐dimensional finite difference time domain (2‐D FDTD) method. Effects of atmospheric structure and topography are included in a vertical section parallel to the wave propagation direction. The simulation successfully reproduced the variations of amplitudes and waveforms. Results are interpreted in terms of wave refraction due to sound and wind speed gradients and wave diffraction at topographic barriers. Our numerical results indicate that both atmospheric and topographic propagation effects are nonnegligible. To evaluate the propagation effects and determine source processes in spatially and temporally varying infrasound data, atmospheric data with a time resolution higher than is currently available are required. If the data are available, the present results suggest that the propagation effects could be evaluated using 2‐D FDTD modeling at realistic calculation times.
Key Points
A long‐term data set spatial‐temporal infrasound propagation is presented
Numerical modeling with atmosphere and topography explains the observation
The propagation effects are non‐negligible and can be evaluated by our model