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.

However there are other typical features associated with the immediate preparation and development of the earthquakes. It is marked the increase of critical frequency fluctuations intensity for sporadic Es layer during two hours before the earthquake on January, 8 and during 8 hours before the earthquake on July, 17. This feature is clearly showed at critical frequency dynamic spectra for Es layer (Fig. 1, right column, the third panel from the top). Vertical line in the figure indicates the start time o f the earthquake. Another feature is the occurrence of synchronous critical frequencies disturbances for different layers associated with the passage of acoustic-gravity waves at days o f earthquakes. For example, on July, 17 synchronous disturbance of critical frequencies F2 and Es layers is observed (Fig. 1, right column, second and third panels from the top). Total number of simultaneous plasma and magnetic disturbances for each considered day is shown in Fig. 2. Thus, the analysis o f the dynamic spectra during the study period showed that magnetogravitational activity increases markedly at two days before and two days after the earthquake. At other days of considered time intervals the level o f magnetogravitational activity remains low. Detection o f magnetogravity waves by ionospheric F2 layer data and magnetic observations 8 January2006 4 ..... A .. - .....-......— .... ............. / \ ___ " \ J \ 5Jan 6Jan 7Jan 8Jan 9Jan 10Jan ll Jan Fig. 2 The number of simultaneous plasma and magnetic disturbances. MGW dispersion relations The possibility of MGW propagation in the ionosphere with account of its finite conductivity was confirmed by analysis o f solutions o f the linearized MHD equations for the collective account of gravity and Ampere force. In these paper here the horizontal direction of the geomagnetic field is considered, which corresponds to the equatorial ionosphere region. Numerical calculations of the dispersion curves for the two propagating fast and one slow MGW modes are shown in Fig. 3. In these case the azimuth angle value is = 4 5 0 and following parameters ionosphere are used: T = 10 3 K, y - 1.4 - the adiabatic, /3= 0.02 , H=3*10 6 cm, H0 = 0.5 G, conductivity o=10 10 s ' 1 and magnetic Reynolds number Rem=3*10 2 [Barkhatova et al., 2012] . The presence of three propagating modes confirms the possibility o f MGW existence in the equatorial region in the conditions close to parameters of ionosphere F2 layer. Experimental analysis o f dynamic spectra o f magnetic and plasma disturbances in the earthquakes intervals was carried out in the frequency range o f 2TO "4 -s- 10 "3 Hz because o f used data time resolution. According to analytical evaluation in this frequency range can be obtained all propagating MGW modes with wavelengths greater than 40 km. Conclusions The study revealed the MGW occurrence during strong (over 6.5 on the Richter scale) underground earthquake at January 8 , 2006 and July 17, 2006. A significant increase of magnetogravitational activity is marked at two days before and two days after the earthquake. During earthquakes magnetogravitational waves are not observed but the passage o f acoustic-gravity waves is noted. Analysis o f MGW dispersion relations confirms the possibility of this wave type propagation at ionosphere F2 layer height in the equatorial region, where the gravity force and geomagnetic field is almost perpendicular to each other. Three propagating MGW modes are analyzed with the establishment of specific propagation directions and frequency ranges for each mode. Thus the results o f experimental and analytical studies suggest the possibility of MGW appearence in the equatorial region o f the ionosphere at intervals of high energy geophysical events. Detected magnetogravitational activity caused by preparation of strong underground earthquakes can be used to development of predicting methods for such large-scale events. 141