Acoustic-Gravity Wave Dynamics in Atmospheric Systems

Acoustic-gravity waves (AGWs) are fundamental oscillations in a stratified atmosphere in which both pressure and buoyancy act as restoring forces. They encompass a spectrum ranging from high-frequency acoustic waves to low-frequency internal gravity waves, mediating energy and momentum transfer between the troposphere, stratosphere, mesosphere and thermosphere. AGWs are generated by a variety of sources, including convection, orography, jet-stream instabilities, severe weather and seismic or tsunamigenic disturbances. Their propagation is governed by dispersion relations that couple sound speed, buoyancy frequency and background wind and temperature profiles. As AGWs ascend, they interact nonlinearly, undergo wave-mean-flow exchanges and can reach amplitudes sufficient to trigger instabilities or turbulence. Observationally, AGWs are monitored by satellite lidar and airglow imaging, radar systems, radiosondes and ground-based lidars, while numerical models resolve their multiscale dynamics. These waves influence large-scale circulation phenomena such as the quasi-biennial oscillation and sudden stratospheric warming, drive thermospheric variability and modulate ionospheric irregularities. Understanding AGW dynamics enhances weather and climate prediction, supports space-weather forecasting and underpins novel remote-sensing applications for natural hazards.

Research from Nature Portfolio

Recent studies have employed advanced satellite lidar observations alongside high-resolution global circulation models to characterise AGW propagation into the mesosphere and lower thermosphere, revealing seasonal modulation of wave amplitudes by background winds. One investigation combined ground-based airglow imaging with numerical simulations to trace AGWs generated by tropical convection, quantifying their role in stratospheric momentum deposition. A further study introduced a hybrid fluid-kinetic modelling framework that elucidated how small-scale AGWs seed ionospheric irregularities and affect radio-signal propagation, thereby linking lower-atmosphere disturbances to space-weather phenomena.

Acoustic-Gravity Wave Dynamics in Atmospheric Systems publication trend

The graph below shows the total number of articles in acoustic-gravity wave dynamics in atmospheric systems across all publications each year (not limited to Nature Index journals).

Technical terms

Acoustic-gravity wave (AGW): A coupled oscillation in a stratified atmosphere restored by pressure (acoustic) and buoyancy (gravity) forces, spanning frequencies between sound waves and internal gravity waves.

Brunt–Väisälä frequency: The natural frequency of vertical oscillation for a displaced parcel in a stably stratified fluid, setting the upper limit for internal gravity wave frequencies.

Evanescent mode: A wave solution satisfying the dispersion relation that decays exponentially with distance from a source or boundary, rather than propagating freely.

Modulational instability: A nonlinear process whereby a uniform wave train becomes unstable to perturbations, leading to energy localisation, amplitude modulation and possible wave collapse.

Hodograph analysis: A technique using the polarisation relationship between wind-speed and temperature perturbations to infer wave properties from radiosonde or in situ measurements.

References

1. Modulational instability and collapse of internal gravity waves in the atmosphere. Physical Review E (2024).
2. Evanescent acoustic-gravity modes in the isothermal atmosphere: systematization and applications to the Earth and solar atmospheres. Annales Geophysicae (2019).
3. Improvement of methods for studying internal gravity waves in the Earth’s atmosphere using radiosonde measurements. Journal of Physics Conference Series (2020).