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

Abstract

S U M M A R YWe 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.

Simulating the dependence of seismo-ionospheric coupling on the magnetic field inclination

“…Employing 1-D and 3-D normal-mode modelling, Artru et al (2004) showed that the surging time and amplitude of ionospheric response are similar in 1-D and 3-D approaches. This is expected since the low-latitude ionospheric change is mainly governed by the infrasonic wind component perpendicular to the magnetic field (Kherani et al, 2009). On this basis, the results in the present study of 1-D modelling are reasonable to the first order.…”

Gravity wave initiation of equatorial spread F/plasma bubble irregularities based on observational data from the SpreadFEx campaign

“…The divergence-free current density condition ∇·δJ =0 implies ∇·δE=0 (Kherani et al, 2009c). The unstable GRTI wave is low-frequency wave (Kelley, 1989) for which the second term in the above equation can be ignored.…”

Modeling of local disturbance formation in the ionosphere electron concentration before strong earthquakes

“…It is known that IGWs of tropospheric origin produce this kind of amplitudes. These amplitudes are also obtained by using a realistic simulation of the IGWs during the Sumatra tsunami (Occhipinti et al, 2006(Occhipinti et al, , 2008Alam Kherani et al, 2009). Wind measurements in the lower thermosphere (MLT-radar for example) have measurement errors of ∼10 m s −1 (Forbes et al, 1999).…”