The Dynamics of Nonlinear Atmospheric Acoustic‐Gravity Waves Generated by Tsunamis Over Realistic Bathymetry

Abstract

The investigation of atmospheric tsunamigenic acoustic and gravity wave (TAGW) dynamics, from the ocean surface to the thermosphere, is performed through the numerical computations of the 3D compressible nonlinear Navier-Stokes equations. Tsunami propagation is first simulated using a nonlinear shallow water model, which incorporates instantaneous or temporal evolutions of initial tsunami distributions (ITD). Ocean surface dynamics are then imposed as a boundary condition to excite TAGWs into the atmosphere from the ground level. We perform a case study of a large tsunami associated with the 2011 M9.1 Tohuku-Oki earthquake and parametric studies with simplified and demonstrative bathymetry and ITD. Our results demonstrate that TAGW propagation, controlled by the atmospheric state, can evolve nonlinearly and lead to wave self-acceleration effects and instabilities, followed by the excitation of secondary acoustic and gravity waves (SAGWs), spanning a broad frequency range. The variations of the ocean depth result in a change of tsunami characteristics and subsequent tilt of the TAGW packet, as the wave's intrinsic frequency spectrum is varied. In addition, focusing of tsunamis and their interactions with seamounts and islands may result in localized enhancements of TAGWs, which further indicates the crucial role of bathymetry variations. Along with SAGWs, leading long-period phases of the TAGW packet propagate ahead of the tsunami wavefront and thus can be observed prior to the tsunami arrival. Our modeling results suggest that TAGWs from large tsunamis can drive detectable and quantifiable perturbations in the upper atmosphere under a wide range of scenarios and uncover new challenges and opportunities for their observations.

Conjugate Effect of the 2011 Tohoku Reflected Tsunami‐Driven Gravity Waves in the Ionosphere

“…This also agrees well with previous observations that TIDs trailing behind the tsunami oceanic waves tend to have ∼10-60 min delay (e.g., Artru et al, 2005;Azeem et al, 2017;Galvan et al, 2012;Rolland et al, 2010). Our observations essentially support Inchin et al (2020), although TIDs traveling ahead of the tsunami cannot be identified. The motions of ions and neutrals in the ionosphere are not necessarily coincident because the presence of geomagnetic field lines and ion drag could substantially affect the ion-neutral coupling (e.g., Liu & Yeh, 1969).…”

“…The tsunami features are also consistent with the MSTID observations (Figures 1 and 2) that the amplitudes of MSTIDs are increased when propagating southwestward, and the durations of MSTIDs are ∼1-2 hr (Figure 3), suggesting that the reflected tsunami should be the source to trigger the MSTIDs. This is also supported by simulations that the tsunami reflected by the Emperor Seamount Chain can excite TIDs propagating toward Japan (Inchin et al, 2020).…”

“…Albeit the peak periods of MSTIDs (24-36 min) over Japan tend to be smaller than the DART 21418 observations (36 min). Inchin et al (2020) suggested that the tsunami-induced gravity wave spectrum has phase variations from long-period phases at the head of the packet to short-period phases at its tail. The long-period waves are leading waves traveling simultaneously with or ahead of the tsunami, with smaller vertical wavelengths and longer periods that could dissipate at lower altitudes, leading to weak TEC perturbations (Galvan et al, 2012;Vadas, 2007).…”

Impacts of the January 2022 Tonga Volcanic Eruption on the Ionospheric Dynamo: ICON‐MIGHTI and Swarm Observations of Extreme Neutral Winds and Currents

“…Although no numerical models have yet simulated the upper atmospheric response to the Tonga Lamb wave, Inchin, Heale, et al. (2020) provide a discussion on these processes using a first‐principles model of the thermospheric signature of tsunamis.…”

Rapid Conjugate Appearance of the Giant Ionospheric Lamb Wave Signatures in the Northern Hemisphere After Hunga‐Tonga Volcano Eruptions

“…By comparing with the intense tsunami effect of the 2011 Tohoku earthquake, there were leading TIDs ahead of the tsunami arrival (e.g., Makela et al, 2011). Inchin et al (2020) suggest that the tsunami-induced gravity wave spectrum has phase variations from long-period phases at the head of the packet to short-period phases at its tail. A similar process might occur in this event, where, instead of the tsunami exciting the gravity waves, the surface Lamb wave might excite a broad spectrum of gravity waves.…”