Recent ionospheric observations report anomalous total electron content (TEC) deviations prior strong earthquakes. We discuss common fetures of the pre-earthquake TEC disturbances on the basis of statistics covering 50 strong seismic events during 2005-2006. The F2-layer ionospheric plasma drift under action of the electric fields of seismic origin is proposed as the main reason of producing TEC anomalies. The origin of such electric fields is discussed in terms of the lithosphere-atmosphere-ionosphere coupling system. This theory is supported by numerical simulations using global Upper Atmosphere Model (UAM). UAM calculations show that the vertical electric current with the density of about 20 - 40 nA/m² flowing between the Earth and ionosphere over an area of about 200 by 2000 km is required to produce the TEC disturbances with the amplitude of about 30% - 50% relatively to the non-disturbed conditions. Ionosphere responses on the variations of the latitudinal position, direction and configuration of the vertical electric currents have been investigated. We show that not only the vertical component of the ionospheric plasma drift but also horizontal components play an important role in producing pre-earthquake TEC disturbances

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The lithosphere‐atmosphere‐ionosphere coupling problem is a challenge nowadays. It requires understanding of (a) the physical mechanism that is responsible for plasma disturbances generation at ionospheric heights, (b) the penetration of seismogenic impact from the ground into the ionosphere through the underlying neutral atmosphere, and (c) on‐the‐ground (in‐the‐ground) sources generation. Kuo et al. (2014) reported an improved model of lithosphere‐atmosphere‐ionosphere coupling that includes the ionosphere as well as the underlying neutral atmosphere (from the ground up to the ionosphere altitudes, i.e., 60–80 km above the Earth's surface). The main feature of the Kuo et al. (2014) approach is that they find ground‐to‐ionosphere currents from ∇·trueJ→=0, trueJ→≡−∇ψ system of equations. In contrast to Kuo et al. (2011), where well‐known ∇·trueJ→=0,trueJ→=trueσ̂trueE→,trueE→=−∇ϕ equations are used, Kuo et al. (2014) looks better as it does not require the knowledge of electric conductivity σ profile. In this paper we show that the Kuo et al. (2014) equations can be obtained as a special case of the Kuo et al. (2011) ones, given the electric conductivity tensor is a spatially invariant scalar. Therefore, Kuo et al. (2014) formulation may not describe correctly electric currents flowing between the Earth and the ionosphere.