[M-TT39] Brand-new scope of coupling geophysics being established by infrasound and associated waves

[MTT39-11] Infrasound to 300 km? Reevaluating Upper-Atmospheric Wave Dissipation with Weak-Shock Modeling

★Invited Papers

*Hiroaki Saito¹ (1.Chitose Institute of Science and Technology)

Keywords:infrasound, weak-shock wave, energy dissipation

We investigate the potential for infrasound (low-frequency acoustic waves), excited by volcanic eruptions, earthquakes, and tsunamis, to form weak shocks and undergo significant dissipation in the rarefied upper atmosphere. Conventional linear or classical absorption models—considering viscosity and thermal conduction—suggest that waves below ~1 Hz can propagate up to around 300 km altitude. However, if the relative amplitude (particle velocity) becomes large enough at high altitudes, the Mach number may exceed unity, triggering a “weak-shock” regime with enhanced nonlinear dissipation.
In this presentation, we introduce a one-dimensional vertical model incorporating weak-shock losses to reassess how much energy infrasound can retain while traveling upward. Our numerical results indicate that shock formation can critically limit the wave’s reachable altitude. Moreover, understanding such wave dissipation processes is also relevant to planetary atmospheric studies: for instance, constraining energy transport and wave-driven dynamics in the upper atmosphere can offer insights into the supply and escape mechanisms of water (and hydrogen) on Earth and Mars. This perspective aligns with broader efforts to elucidate the origin and circulation of water in planetary environments.