Propagation of tsunami‐driven gravity waves into the thermosphere and ionosphere

Recent observations have revealed large F‐region electron density perturbations (∼100%) and total electron content (TEC) perturbations (∼30%) that appear to be correlated with tsunamis. The characteristic speed and horizontal wavelength of the disturbances are ∼200 m/s and ∼400 km. We describe numerical simulations using our spectral full‐wave model (SFWM) of the upward propagation of a spectrum of gravity waves forced by a tsunami, and the interaction of these waves with the F‐region ionosphere. The SFWM describes the propagation of linear, steady‐state acoustic‐gravity waves in a nonisothermal atmosphere with the inclusion of eddy and molecular diffusion of heat and momentum, ion drag, Coriolis force, and height‐dependent mean winds. The tsunami is modeled as a deformation of our model lower boundary traveling at the shallow water wave speed of 200 m/s with a maximum vertical displacement of 50 cm and described by a modified Airy function in the horizontal direction. The derived vertical velocity spectrum at the surface describes the forcing at the lower boundary of the SFWM. A steady‐state 1‐D ionospheric perturbation model is used to calculate the electron density and TEC perturbations. The molecular diffusion strongly damps the waves in the topside (>300‐km altitude) ionosphere. In spite of this, the F‐region response is large, with vertical displacements of ∼2 to 5 km and electron density perturbations of ∼100%. Mean winds have a profound effect on the ability of the waves to propagate into the F‐region ionosphere.