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). 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-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.