Upper Atmospheric Responses to Surface Disturbances: An Observational Perspective

We review observations on the coupling between Earth's surface disturbances and the upper atmosphere. In particular, we focus on the upper atmospheric responses to atmospheric acoustic-gravity waves generated during impulsive surface disturbance events including earthquakes, tsunamis, volcanic eruptions, and explosions. We review the theoretical background for the generation and propagation of atmospheric acoustic-gravity waves from surface disturbance events as well as of the ionospheric plasma response to such acoustic-gravity waves. We review a variety of observational techniques that have been successfully utilized to detect upper atmospheric perturbations induced by surface disturbances and summarize the state-of-the-art knowledge on the coupling processes learnt from these observations. Finally, we touch on some most recent advances in the field and propose directions for future research. Plain Language Summary Earthquakes, tsunamis, volcanic eruptions, and chemical and nuclear explosions on or under the ground create sudden and violent motions of the ground or ocean surface. While ground shakings during some massive earthquakes can be felt by people who live thousands of kilometers away from the epicenters, the shakings can also be detected from the atmosphere hundreds of kilometers above the ground (upper atmosphere). Similarly, tsunamis, volcanic eruptions, and explosions can have footprints in the upper atmosphere as well. These footprints have been successfully detected by a variety of observational techniques. This paper reviews the observational results and the current understanding of the physical mechanisms behind the coupling between the ground/ocean and the upper atmosphere. In addition, future research directions are proposed in order to address the open questions.