Response of the ionosphere to the seismic trigerred acoustic waves: electron density and electromagnetic fluctuations

Abstract : We study the excitation of low-frequency (0.001-10 Hz) electromagnetic and density fluctuations in the ionosphere during the passage of seismic triggered acoustic waves (AWs). The study involves the generation of ionospheric currents by AWs and subsequent perturbations of the electromagnetic fields and ion and electron density. In this study, the non-local analysis of the fluctuations is carried out in the framework of hydromagnetic theory. Our objective is to examine the spatial and frequency distributions of these fluctuations and to compare them qualitatively with the available observations. The dynamics of both electrojet and F region of ionosphere are included. Also included are the effects of the dip-angle variations of the Earth's magnetic field. Significant anisotropy and inhomogeneities are noted in the fluctuations. The amplitudes of current and magnetic field fluctuations are found to be maximum in the F region where ion inertia is large enough to support the plasma waves and where electron number density and acoustic wave amplitudes are also large. The density fluctuations also follow similar trends. Both electromagnetic and density fluctuations are large in the latitude region where the acoustic wave vibration parallel to the Earth's magnetic field is large. The fluctuations have the tendency to be maximum in the 0.1-1 Hz frequency range. In this range, AWs driven currents and electromagnetic fluctuations may become of order of μAm −2 , nV m −1 and nT, respectively in the F region.