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.

Physics o fAuroral Phenomena ", Proc. XXXIV Annual Seminar, Apatity, pp. 133 - 136 2011 © Kola Science Centre, Russian Academy o f Science, 2011 Polar Geophysical Institute EAR TH QU AK E S ’ IN FLU EN C E ON TH E SPACE W EATH ER A.A. Namgaladze (Murmansk State Technical University , Abstract. The Total Electron Content anomalies observed before strong earthquakes have been considered as possible ionospheric earthquakes precursors. Their possible physical mechanism related with seismogenic electric field has been supposed and the results of the numerical modeling of the ionospheric effects of the seismogenic electric field have been discussed. Introduction Nowadays GNSS-based (Global Navigation Satellite Systems) techniques are widely used to investigate the ionosphere TEC (Total Electron Content) modifications and in particular the ionospheric effects associated with seismic events. The dense network of GNSS and GPS (Global Positioning System) receivers fulfills simultaneous coverage in global scale and allows to plot and analyze the global maps of the TEC. The TEC is the integral amount of electrons in the vertical column with 1 m2cross-section over the given point. The main contribution in the TEC is produced by the ionospheric F2-layer electron density (heights 200-1000 km), i.e. by the region of the maximal ionospheric electron density. The time variations of TEC and NmF2 are very similar. Therefore, we can consider both TEC and NmF2 variations as equally important space weather characteristics. Morphology of the TEC anomalies observed before strong earthquakes The extensive studies of the ionospheric earthquake precursors in the GPS TEC measurements [e.g. Liu et al, 2004, 2006; Pulinets et a l, 2003; Pulinets and Boyarchuk, 2004; Pulinets and Ouzhounov, 2010; Zakharenkova et al. 2007a,b; 2008] revealed that for strong mid-latitudinal earthquakes the seismo-ionospheric anomalies very often look like: (1) local long-living TEC increases or depressions that are situated in the vicinity of the earthquake epicenter area. The amplitude of plasma modification reaches the values of 30-90% relative to the non-disturbed level. Positive modifications of the TEC usually dominate. (2) The vertical projection of the epicenter position does not mandatory coincide with the maximum phenomenon's manifestation location. (3) The zone of the anomaly maximum manifestation extends larger than 1500 km in latitude and 3500-4000 km in longitude. The shapes and dimensions of the disturbed areas are kept rather stable. (4) The size of the area depends on the earthquake's magnitude. (5) Similar effects are often reported at the magnetically conjugated area. (6) The anomalies are reported from several days or hours to couple weeks before the earthquake release moment. (7) In case of the strong low-latitudinal earthquakes there are effects related to the modification of the ionospheric F2-region equatorial anomaly: increase or decrease of the equatorial anomaly with trough deepening or filling. This traditional pre-earthquake TEC modification scheme, reported by many authors, should be extended with the following two new signatures revealed in some recent investigations of the last strong earthquakes: (8) “Ban-time” effect at the near-noon hours [Namgaladze et al, 2011], i.e. the TEC anomaly reduction with subsolar point income takes place, and (7) sun-rise terminator income should trigger anomaly depletion while sun-set terminator income trigger the anomaly recovery. It should be noticed that many ULF precursors also dominate at night-time (see, e.g. [Hobara et al, 2004]). Physical interpretation of the TEC anomalies observed before strong earthquakes We consider that the most probable reason of the NmF2 and TEC disturbances observed before the earthquakes is the vertical drift of the F2-region ionospheric plasma under the influence of the zonal electric field of seismogenic origin. Due to the high electrical conductivity of the geomagnetic field lines they can be assumed to be electrical equipotentials, so that electric fields along these lines are zero or very small. Electric fields at heights > 170 km are therefore practically always perpendicular to the geomagnetic field lines. These mutually perpendicular electric (E) and magnetic (B) fields force the ionospheric plasma to move with the so called ExB plasma drift velocity (equal to ExB/B2), i.e. in the direction perpendicular to both. In this drift motion, ions and electrons move together with the same velocity, i.e. there is no charge separation and they do not create electric currents. 133