Physics of auroral phenomena : proceedings of the 34th Annual seminar, Apatity, 01 - 04 March, 2011 / [ed.: A. G. Yahnin, A. A. Mochalov]. - Апатиты : Издательство Кольского научного центра РАН, 2011. - 231 с. : ил.

A.A. Namgaladze et al. In the middle latitudes the upward electromagnetic drift, created by the eastward electric field, leads to the increase of the NmF2 and TEC due to the plasma transportation to the regions with lower concentration of the neutral molecules and, consequently, with lower loss rate of dominating ions 0+ in the ion-molecular reactions. The electric field of the opposite direction (westward) creates the opposite - negative - effect in NmF2 and TEC. In the low latitude regions (near the geomagnetic equator) the increase of the eastward electric field leads to the deepening of the equatorial anomaly minimum (“trough” over the magnetic equator in the latitudinal distribution of electron concentration) due to the intensification of the fountain-effect [Brunelli and Namgaladze, 1988]. The TEC is formed mainly by the F2-layer plasma density. NmF2 and TEC disturbances related with magnetic activity are created by the neutral atmosphere (neutral gas composition, internal gravity waves and winds) and electric field variations. But it is impossible to localize neutral atmosphere disturbances at a limited area, they will propagate away from the source. Therefore, there are strong arguments in favor of the idea of an electric field of seismic origin as the main cause for the TEC anomalies observed before earthquakes: (a) the geomagnetically conjugate ionospheric precursors [Pulinets et al., 2003]; (b) effects related to the ionospheric F2-region equatorial (Appleton) anomaly controlled by the zonal electric field [Depueva and Ruzhin, 1995; Pulinets and Legen’ka, 2002]; (c) “ban-time” at the near-noon hours [Namgaladze et al., 201 la]. Many authors [e.g., Pulinets and Boyarchuk, 2004; Pulinets and Ouzhounov, 2010; Chmyrev and Sorokin, 1999; Sorokin et al., 2005a,b; 2006, 2007] strongly rely on the hypothesis of a seismogenic electric field related to the vertical turbulent transportation of injected aerosols and radioactive particles (radon isotopes). The increase of the atmospheric radioactivity level during the earthquake formation leads to the enlargement of the ionization and electric conductivity of the near-ground atmosphere. The joint action of these processes leads to an intensification of an electric field in the ionosphere up to the value of units-tens mV/m [Chmyrev et al., 1989]. Ionosphere response on such electric fields were investigated mainly using ID models and for the lower ionosphere [Hegai et al.,1997; Kim et al., 2002]. Freund [2011] proposed another mechanism of the near-ground atmosphere layer ionization basing on the so called “positive holes”: most crustal rocks contain dormant electronic charge carriers in the form of peroxy defects; when rocks are stressed, peroxy links break, releasing electronic charge carriers, known as positive holes. The positive holes are highly mobile and can flow out of the stressed subvolume. F. Freund expects this mechanism to be significantly more efficient than the above-named radon-related ones. Modeling of the TEC anomalies observed before strong earthquakes We have calculated the ionospheric electric field related with external electric current variations in the lower atmosphere. This current is assumed to be formed due to the convective upward transport o f charged aerosols and their gravitational sedimentation in the lower atmosphere and is related with the occurrence of ionization source due to seismic-related emanation of radon and other radioactive elements into the lower atmosphere over the earthquake preparation area [Chmyrev and Sorokin, 1999; Sorokin et al., 2005a,b; 2006, 2007; Pulinets and Boyarchuk, 2004; Pulinets and Ouzhounov, 2010; Pulinets and Tsybulya, 2010] or with the so-called “positive hole” electric field ionization [Freund, 2011]. We used this vertical current as the model input for the calculations of the ionospheric electric field and corresponding TEC variations using the UAM - Upper Atmosphere Model [Namgaladze et al., 1988, 1990, 1998]. The Upper Atmosphere Model is a global, three-dimensional, time-dependent, numerical model simulating the thermosphere, ionosphere, plasmasphere and inner magnetosphere of the Earth as a single system. It was initially developed at the Kaliningrad observatory (now West Department) of IZMIRAN [Namgaladze et al., 1988, 1991] and then extended at the Polar Geophysical Institute of the Russian Academy of Sciences and at the Murmansk State Technical University [Namgaladze et al., 1998a,b]. The model includes the equations of the continuity, momentum and heat balance for neutral and charged particles and the electric potential equation and calculates the concentrations velocity vectors and temperatures of basic neutral (0 2, N2, O) and charged (NO+, 0 2+, 0 +, H+and e) components of the atmosphere at the altitude range from 60 km to 15R,,. To estimate the upper limit for the magnitudes of the vertical electric current applied, we looked through the publications available. Sorokin et al. [2005a,b; 2006, 2007] calculated the ionospheric electric field related to external electric current variations in the lower atmosphere. According to Sorokin et al., an external current density of about 10'6A/m2 within an area of about 200 km in radius (approximately 130 000 km2) is required to create an electric field of several mV/m in the ionosphere. To build model difference maps (of the electric potential, zonal and meridional electric field and TEC) we firstly performed a regular calculation without any additional electric current sources (set as lower boundary condition) to use the results as quiet background values. Then an external electric current flowing between the lower atmosphere and the ionosphere over the Haiti earthquake (Jan. 12, 2010, 21:53 UT, M 7.0) epicenter area has been used as model input for the calculations of the ionospheric electric field and the corresponding TEC variations. Several spatial configurations and magnitudes of these currents have been taken into consideration: (1) “point” 134