Physics of auroral phenomena : proceedings of the 36th Annual seminar, Apatity, 26 February – 01 March, 2013 / [ed. board: A. G. Yahnin, A. A. Mochalov]. - Апатиты : Издательство Кольского научного центра РАН, 2013. - 215 с. : ил., табл.

*Physics o f Auroral Phenomena", Proc. XXXVI Annual Seminar, Apatity, pp. 1 4 7 -1 5 0 , 2013 © Kola Science Centre, Russian Academy of Science, 2013 Polar Geophysical Institute MODELING OF THE TEC DISTURBANCES GENERATED BY SEISMOGENIC ELECTRIC CURRENTS AT DIFFERENT SEASONS M.I. Karpov, A .A . N am galadze (M urmansk State Technical University, Murmansk, Russia) Abstract Numerical calculations of the ionosphere Total Electron Content (TEC) disturbances have been performed using global Upper Atmosphere Model (UAM) for the conditions corresponding to the Haiti (January 12, 2010) and Japan (March 11, 2011) earthquakes. The vertical electric currents with the density 10 nA/m 2 and flowing over the area of about 250 by 4500 km have been setup as the sources of the seismogenic impact at the height of 80 km in the UAM electric potential equation. Their action resulted in the relative (%) modeled TEC disturbances with the same key features as the TEC variations observed before both these earthquakes. Both modeled and observed TEC disturbances for both cases appeared at night near the epicenter and magnetically conjugated area; they were 40- 60 % by magnitude; and did not move away from the source location during their lifetime. In the Haiti case maximum o f both modeled and observed TEC variations was more pronounced in the area magnetically conjugated to the epicenter. In the Japan case both modeled and observed disturbances were more symmetrical relative to the geomagnetic equator. According to the UAM simulations, TEC disturbances that are symmetrical relative to the geomagnetic meridian of the epicenter were obtained by setting up vertical electric currents flowing to the Earth at one side from the epicenter meridian and back currents at the opposite side. Introduction Variations o f the ionospheric total electron content (TEC) registered before strong seismic events have distinctive features and are considered as ionospheric earthquake precursors. The stable long-living positive and negative disturbances (increase or decrease) with the magnitude o f several tens of percents relative to the quiet background values are observed over the epicenter region and often over the magnetically conjugated area. The manifestation zone of these anomalies extends more than 1500 km along the meridian and 3500-4000 km along the parallel, doesn’t change its form and doesn’t move away unlike the traveling ionospheric disturbances associated with geomagnetic activity. The relative TEC disturbances are observed mostly during night-time, reduce significantly after sunrise up to full disappearance and reappear again after sunset. Modifications of the equatorial anomaly are often registered in case of low-latitude earthquakes ( Liu et al., 2004; Pulinets and Boyarchuk, 2004; Depueva and Ruzhin, 1995). Formation o f such TEC disturbances is associated with seismogenic electric fields generated at the ionosphere heights ( Pulinets and Boyarchuk, 2004) as a result of external electric current flowing above epicenter {Sorokin et al., 2007 and references therein). Radon and other radioactive particles emanating from tectonic faults play important role in the process as well as aerosols and soil gases which concentration increases before earthquakes {Alekseev and Alekseeva , 1992; Heincke et al., 1995; Omori et al., 2007). The decay products of radon act as an ionization source of the neutral particles o f the near-surface air layer, and aerosols become charged by interacting with newly formed ions and electrons. The electric current is generated by gravitational sedimentation and convectional transport of charged aerosols o f different sizes. According to estimations performed by (Sorokin et al., 2007) the density of external electric current may reach 1O' 6 —10 '7 A/m 2 and corresponding electric field disturbance in the ionosphere amounts to about 10 mV/m. The same electric field intensity was registered by satellite observations over seismic active regions at the area with horizontal scale of several hundred kilometers and more (Gousheva et al., 2009; Zhang et al., 2013). Electric field generated by charge carriers activated during rock stress and accumulated near the ground surface might act as another or additional ionization source (Freund et al., 2009), and electric current with the density o f 0.5T0'6-1.25-10'6 A/m 2 was registered over 200 cm 2 collector plate in laboratory experiments with stressed rock. The direct action o f the seismogenic electric field on the TEC was proposed in (Namgaladze et al., 2009) via the electromagnetic [E x B] plasma drift in crossing electric E and magnetic В fields responsible for increase or decrease o f the electron number density and, thus, for the TEC positive or negative disturbances. This physical mechanism was successfully verified in the series o f numerical calculations where external electric current of seismic origin was used as an additional input in the electric potential equation. It was shown that sources of electric current with the density of about 1-10 nA/m 2 spread out over the area of 250 by 2000 km create the required electric fields of several mV/m in the ionosphere and generated TEC disturbances are in a good agreement with the anomalies observed before strong earthquakes (Namgaladze et al., 2013). All mentioned general features of the ionospheric precursors were reproduced in simulations, but the density of the electric current used in calculations is 147