ISSN 0016-7932, Geomagnetism and Aeronomy, 2009, Vol. 49, No. 2, pp. 252–262. © Pleiades Publishing, Ltd., 2009. Original Russian Text © A.A. Namgaladze, M.V. Klimenko, V. V. Klimenko, I.E. Zakharenkova, 2009, published in Geomagnetizm i Aeronomiya, 2009, Vol. 49, No. 2, pp. 267–277. 252 1. INTRODUCTION Observable variations in the state of the ionosphere before earthquakes are called ionospheric precursors of these events. Numerous groups of researchers (see, e.g. [Liperovskii et al., 1992] and references in [Zakharenkova, 2007]) have sought these precursors for the last two decades. This search has also been per- formed in the scope of the special-purpose projects of natural disaster space monitoring: COMPASS-1, COMPASS-2, Sich-1M, QuakeSat, and DEMETER. The global system of navigation satellites (GPS) and the network of receivers of signals from these satellites have been widely used to study the ionospheric effects related to seismic activity [Liu et al., 2002, 2004; Plot- kin, 2003; Afraimovich et al., 2004; Zakharenkova et al., 2006; Krankowski et al., 2006]. Measurements of time delays of these signals can be used to map the total electron content (TEC) in the unit-section col- umn and to study the time evolution of this content, which reflects the variations in the maximal electron density (NmF2) in the ionospheric F 2 layer (the main ionospheric maximum). 2. OBSERVATIONS Extensive studies of the ionospheric precursors of earthquakes in TEC have been performed for the last time at the Institute of Terrestrial Magnetism, Iono- sphere, and Radiowave Propagation, Russian Acad- emy of Sciences (IZMIRAN) and its western division (Kaliningrad) together with the Kant Russian State University. In [Zakharenkova et al., 2005, 2006, 2006a, 2006b; Zakharenkova, 2007], it was found that the manifestation of strong midlatitude earthquakes in TEC has the form of a local increase in electron den- sity, which is observed two–three days before an earth- quake, and the disturbed region maximum is located in close proximity to the epicentral region. The spatial scale is several thousand kilometers along the parallel and about 1000 km along the meridian. As we approach an earthquake instant, a disturbance ampli- tude increases and reaches 40–100% of the back- ground level. It was revealed that electron density above an epicentral region tends to decrease 10–30 h before an earthquake. The value of this negative effect can reach –30% relative to an undisturbed state. Under quiet geomagnetic conditions, the sign reversal of a seismoionospheric disturbance can be interpreted Physical Mechanism and Mathematical Modeling of Earthquake Ionospheric Precursors Registered in Total Electron Content A. A. Namgaladze a , M. V. Klimenko b , V. V. Klimenko c , and I. E. Zakharenkova c a Murmansk State Technical University, ul. Sportivnaya 13, Murmansk, 183010 Russia b Kaliningrad State Technical University, Kaliningrad, Russia c Institute of Terrestrial Magnetism, Ionosphere, and Radiowave Propagation, Western Division, Russian Academy of Sciences, pr. Pobedy 41, Kaliningrad, 236017 Russia e-mail: namgaladzeaa@mstu.edu.ru Received July 7, 2008; in final form, September 23, 2008 Abstract—The physical mechanism by which the regions with increased or decreased total electron content, registered by measuring delays of GPS satellite signals before strong earthquakes, originate in the ionosphere has been proposed. Vertical plasma transfer in the ionospheric F 2 region under the action of the zonal electric field is the main disturbance formation factor. This field should be eastward, generating the upward compo- nent of plasma electromagnetic drift, in the cases of increased total electron content at midlatitudes and deepened minimum of the F 2 layer equatorial anomaly. Upward plasma drift increases electron density due to a decrease in the O + ion loss rate at midlatitudes and decreases this density above the equator due to an enhancement of the fountain effect (plasma discharge into the equatorial anomaly crests). The pattern of the spatial distribution of the seismogenic electric field potential has been proposed. The eastward electric field can exist in the epicentral region only if positive and negative electric charges are located at the western and eastern boundaries of this region, respectively. The effectiveness of the proposed mechanism was studied by modeling the ionospheric response to the action of the electric field generated by such a charge configuration. The results of the numerical computations indicated that the total electron content before strong earthquakes at middle and low latitudes is in good agreement with the observations. PACS numbers: 91.30.Px, 94.20.dj DOI: 10.1134/S0016793209020169