Manifestations of the earthquake preparations in the ionosphere total electron content variations

Abstract

Recent ionospheric observations report anoma- lous total electron content (TEC) deviations prior strong earthquakes. We discuss common fea- tures of the pre-earthquake TEC disturbances on the basis of statistics covering 50 strong seis- mic events during 2005-2006. The F2-layer iono- spheric 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 re- sponses on the variations of the latitudinal po- sition, 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.