11:00 AM - 11:15 AM
[MTT38-07] Numerical Simulation of Various Kinds of Atmospheric Waves Excited by Tsunamis: Lamb waves, gravity waves, acoustic waves
Keywords:Atmospheric Lamb Waves, infrasound, acoustic waves, gravity waves, tsunamis, tsunami early warning
Background
During tsunami generation, various types of atmospheric waves (Lamb waves, gravity waves, and sound waves) are excited from the source region. The excitation mechanism and magnitude of Lamb waves are relatively clearly understood, but the excitation of other types of waves, especially sound waves, is still under debate. The propagation of sound waves after excitation has been discussed in ray theory, which does not directly include information such as the sign, duration, and frequency of the initial motion. However, it is possible that sound waves also contain significant information about tsunamis, so that more detailed examination should be given. In this presentation, we numerically solve the equations of motion for compressible atmospheres and specifically discuss the aspects of tsunami induced atmospheric waves.
Methods
The linearized equations of motion of the compressible atmosphere in two dimensions are numerically solved. A stationary atmosphere is assumed as the basic field, and a standard temperature structure including troposphere, stratosphere, mesosphere, and thermosphere is assumed. The lower surface of the atmosphere is coupled with the shallow water equations describing a tsunami. Waves are excited by providing a localized fault motion with a short rise time at the ocean floor. This system produces tsunamis and the atmospheric waves strongly coupled to tsunamis, but in this presentation we focus exclusively on the various atmospheric waves that propagate much faster than tsunamis, whose dynamics is mostly decoupled from tsunamis.
Results
The initial phase of the excitation is recognized as sound waves isotropically propagating verticaly and horizontaly. Then, in the mean time, it disperses into Lamb waves, gravity waves, and sound waves. That is, the portion of wave emitted laterally disperses into Lamb waves with periods of several minutes, and sound waves with relatively short periods that bounce between the stratopause and the ground surface. The portion of wave emitted upward disperses into gravity waves, having periods of several minutes or longer and slower phase speeds, and sound waves that turn in the lower thermosphere and bounce between the ground and the stratosphere. Interesting aspects include that the initial motion of the stratospheric turning sound wave is negative close to the wave source, and maintains a relatively pulsed structure at a distance, while the thermosphere turning reaches to the ground as a harmonic wave packet lasting for a relatively long period of time. These aspects will be discussed in detail on the day of the presentation.
During tsunami generation, various types of atmospheric waves (Lamb waves, gravity waves, and sound waves) are excited from the source region. The excitation mechanism and magnitude of Lamb waves are relatively clearly understood, but the excitation of other types of waves, especially sound waves, is still under debate. The propagation of sound waves after excitation has been discussed in ray theory, which does not directly include information such as the sign, duration, and frequency of the initial motion. However, it is possible that sound waves also contain significant information about tsunamis, so that more detailed examination should be given. In this presentation, we numerically solve the equations of motion for compressible atmospheres and specifically discuss the aspects of tsunami induced atmospheric waves.
Methods
The linearized equations of motion of the compressible atmosphere in two dimensions are numerically solved. A stationary atmosphere is assumed as the basic field, and a standard temperature structure including troposphere, stratosphere, mesosphere, and thermosphere is assumed. The lower surface of the atmosphere is coupled with the shallow water equations describing a tsunami. Waves are excited by providing a localized fault motion with a short rise time at the ocean floor. This system produces tsunamis and the atmospheric waves strongly coupled to tsunamis, but in this presentation we focus exclusively on the various atmospheric waves that propagate much faster than tsunamis, whose dynamics is mostly decoupled from tsunamis.
Results
The initial phase of the excitation is recognized as sound waves isotropically propagating verticaly and horizontaly. Then, in the mean time, it disperses into Lamb waves, gravity waves, and sound waves. That is, the portion of wave emitted laterally disperses into Lamb waves with periods of several minutes, and sound waves with relatively short periods that bounce between the stratopause and the ground surface. The portion of wave emitted upward disperses into gravity waves, having periods of several minutes or longer and slower phase speeds, and sound waves that turn in the lower thermosphere and bounce between the ground and the stratosphere. Interesting aspects include that the initial motion of the stratospheric turning sound wave is negative close to the wave source, and maintains a relatively pulsed structure at a distance, while the thermosphere turning reaches to the ground as a harmonic wave packet lasting for a relatively long period of time. These aspects will be discussed in detail on the day of the presentation.