Analyses Of The Atmospheric Response In The Neutral Viscous Atmosphere Induced By The Tsunamis

Tsunami usually is coherent over extremely long distances with wave fronts typically a few thousand km in length. This line source would produce waves that propagate upward with only modest geometric spreading, thus increasing their expected amplitudes at high altitudes and increasing their probability of detection. The paper has solely chosen the 2011 Tohoku and 2004 Sumatra tsunami as two representatives of the mid-latitude and low-latitude, respectively. In the simulations, we employ a linear, steady-state full-wave model that allows us to examine the detailed propagation properties of the gravity waves and a two-dimensional, nonlinear model to describe the evolution of an upward propagating Gaussian gravity wave packet in a windy and non-isothermal atmosphere, which takes into account the dissipation due to eddy and molecular processes. The research work of this paper could support a few observations of such atmospheric gravity waves in the ionosphere in the future, and would be very helpful to an early off shore detection of tsunami.Due to less magnetic inclination influence below the E-layer, the E-region ionospheric response is mainly dominated by gravity wave amplitude. Through comparative analyses of the atmospheric responses induced by different propagation directions of gravity waves, we demonstrate that the results associated with the 2011 Tohoku tsunami explained well the observed strong TIDs phenomenon in Japan, occurring in the northwest direction from the epicenter. The strong atmospheric response is identified in about 50 min after the tsunami onset, which occurred in the E-region ionosphere. Nevertheless, the southeastward propagating waves dominated in the F-region ionosphere later due to the significant effects of molecular viscosity and thermal conductivity. In the 2004 Sumatra tsunami event, the atmospheric disturbance response in the lower thermosphere is dominated by gravity waves with the N250°E direction. In the F-region ionosphere, the tsunami occurring at the low latitudes was seriously affected by magnetic inclination, so the gravity waves propagating in the N340°E direction can be observed more easily.The research in this paper has been solely devoted to the neutral response to a gravity wave packet propagating in the atmosphere. F-region ionospheric responses differ with different latitudes actually, so we should consider the ion dynamics and chemistry to study the ionospheric response to the tsunamis in the near future.