9:00 AM - 10:30 AM
[MTT37-P01] Characteristics of atmospheric Lamb waves excited by various geophysical phenomena
Keywords:atmospheric Lamb waves, collision of meteorites, volcanic eruption, Atmospheric free oscillation
1. Introduction
It is still fresh in our memory that large-amplitude atmospheric Lamb waves were excited by the eruption of the Tongan undersea volcano in January last year and encircled the earth several times. Such distinct lamb waves have been observed in the past with large volcanic eruptions, tsunamis, nuclear tests, and meteoritic impacts. On the other hand, it is also known that the Lamb waves are not one-shot events like these, but are also constantly excited. In this presentation, I will discuss the excitation of Lamb waves by a wide range of geological phenomena, focusing on both episodic and non-episodic excitation.
2. Definition of Atmospheric Lamb Waves
Atmospheric Lamb wave is, in a broad sense, an atmospheric oscillation that is trapped along the ground and has a hydrostatic vertical structure. In terms of horizontal propagation characteristics, it propagates at nearly the speed of sound in the case in which the Coriolis force is not involved (gravity wave-like), while the phase speed is slower in the case of a planetary-scale structure in which the Coriolis force is involved (Rossby wave-like). The latter are often referred to as "free oscillating Rossby waves.
3. Signature of Excitation
The sign of the Lamb wave is governed by the pressure deviation in the lower atmosphere that the source creates in the process of hydrostatic pressure regulation. Specifically, a rise in the lower boundary of the atmosphere due to a tsunami or crustal movement creates a positive Lamb wave, heating of the lower atmosphere or the release of volcanic gases creates a positive Lamb wave, but vertical momentum sources (e.g., drag by solid materials) do not excite Lamb waves.
4. Spatio-Temporal Structure of Excitation Sources
Spatio-temporally localized sources such as volcanic explosions excite Lamb waves with concentrically spread wavefronts. On the other hand, globally distributed excitation sources, such as excitation by condensation heating in a cumulus cloud, are better considered expanded in wavenumber space.
5. Examples
We consider volcanic and meteorite impacts as Lamb waves excited by localized sources, and constant excitation of atmospheric free oscillations as Lamb waves excited by globally distributed sources. For detail on the Lamb waves excited by meteoritic impacts, please refer to the presentation in the session on planetary defense (M-ZZ45).
Acknowledgments: This work was supported by MEXT KAKENHI JP21K21353 and JSPS KAKENHI JP22K18872.
It is still fresh in our memory that large-amplitude atmospheric Lamb waves were excited by the eruption of the Tongan undersea volcano in January last year and encircled the earth several times. Such distinct lamb waves have been observed in the past with large volcanic eruptions, tsunamis, nuclear tests, and meteoritic impacts. On the other hand, it is also known that the Lamb waves are not one-shot events like these, but are also constantly excited. In this presentation, I will discuss the excitation of Lamb waves by a wide range of geological phenomena, focusing on both episodic and non-episodic excitation.
2. Definition of Atmospheric Lamb Waves
Atmospheric Lamb wave is, in a broad sense, an atmospheric oscillation that is trapped along the ground and has a hydrostatic vertical structure. In terms of horizontal propagation characteristics, it propagates at nearly the speed of sound in the case in which the Coriolis force is not involved (gravity wave-like), while the phase speed is slower in the case of a planetary-scale structure in which the Coriolis force is involved (Rossby wave-like). The latter are often referred to as "free oscillating Rossby waves.
3. Signature of Excitation
The sign of the Lamb wave is governed by the pressure deviation in the lower atmosphere that the source creates in the process of hydrostatic pressure regulation. Specifically, a rise in the lower boundary of the atmosphere due to a tsunami or crustal movement creates a positive Lamb wave, heating of the lower atmosphere or the release of volcanic gases creates a positive Lamb wave, but vertical momentum sources (e.g., drag by solid materials) do not excite Lamb waves.
4. Spatio-Temporal Structure of Excitation Sources
Spatio-temporally localized sources such as volcanic explosions excite Lamb waves with concentrically spread wavefronts. On the other hand, globally distributed excitation sources, such as excitation by condensation heating in a cumulus cloud, are better considered expanded in wavenumber space.
5. Examples
We consider volcanic and meteorite impacts as Lamb waves excited by localized sources, and constant excitation of atmospheric free oscillations as Lamb waves excited by globally distributed sources. For detail on the Lamb waves excited by meteoritic impacts, please refer to the presentation in the session on planetary defense (M-ZZ45).
Acknowledgments: This work was supported by MEXT KAKENHI JP21K21353 and JSPS KAKENHI JP22K18872.