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. XXXIVAnnual Seminar, Apatity, pp. 121 -124 2011 © Kola Science Centre, Russian Academy of Science, 2011 Polar Geophysical Institute AN A LY S IS OF D ISPERSION EQUATIONS FOR M AGN ETO GRAV ITY W AVE S IN R E A L IST IC IONOSPHERE 0 .M . Barkhatova1,2, N.A. Barkhatov1,2'3, G.I. Grigoriev3, S.E. Revunov2 1. N izhniy N ovgorod Sta te U niversity o f A rchitecture a n d C ivil Engineering, N izhniy Novgorod, Russia 2. N izhniy N o vgo rod Sta te P edagog ica l University, N izhn iy Novgorod, Russia 3. R adiophysical R research In stitu te (N IRFI), N izhn iy Novgorod, Russia Abstract. In the framework of the magnetohydrodynamic approach we obtain the dispersion equations for magnetogravity waves in the ionosphere taking into account the finite conductivity and the combined effect of magnetic field and gravity. The source of magnetogravity waves propagating in the equatorial direction the auroral electrojet is selected. Experimental observation of magnetogravity waves was based on data analysis of ionospheric F2 layer vertical sounding and on the values of geomagnetic field horizontal component. Based on the data of vertical sounding characteristic frequencies (10*4 - 4 • 1СГ4 Hz) and velocities (over 2000 m / s) of magnetogravity waves were estimated. In this frequency range such values are consistent with the analytical parameters of fast and slow propagating magnetogravity waves modes. 1 Introduction Among the possible sources of wave disturbances in the ionosphere, including traveling ionospheric disturbances (TIDs), often the auroral electrojet is considered. Well known is moving of ionospheric disturbances from auroral region to middle and low latitudes by acoustic-gravity waves (AGW) of different spatial scales. The ionosphere is a conductive space, so there in addition to AGW magnetogravity waves (MGW) can propagate. Characteristic velocities of MGW are greater than AGW, but lower than magnetohydrodynamic (MHD) waves [Sorokin and Fedorovich, 1982]. Experimental confirmation of MGW existence in the ionosphere at altitudes of the F2 layer are obtained in [Barkhatova et al, 2009]. In this work the MGW dispersion equations for infinite conductivity space are analyzed. In this paper the MGW dispersion equations in the ionosphere with finite conductivity are obtained. For this purpose the combined effect of magnetic field and gravity in hydrodynamics equations is considered. This must be done in case of magnetic pressure is comparable to or higher than the hydrostatic pressure and the frequencies of studied waves is much smaller than frequency of neutrals-ions collisions. These conditions are satisfied in the ionosphere from a height about 250 km. 2 The basic system of MGW equations Analysis of MGW propagation conditions for finite conductivity space G with absence of regular winds may be conducted on the basis of magnetohydrodynamic equations. The initial system of linearized equations in this case was chosen as: /?o ^ = - V/ ?+ /c,g + - ( j x H o )’ ~ r~ + A) divD + (uV)/?0 = 0 , dt с dt ^ - + (W) p0=Vs2[ ^ - + (vV)p0] , j = <r{E+ i ( u 4 H 0)} (1) dt ot с 4к j- u л г. 1 Sh roth = — j, d i v h = 0 , rotE = ----- — с с dt Here p - medium density, p - pressure, D - velocity, h - magnetic field, Vs2 - the square of adiabatic sound speed, у - the adiabatic constant, g - gravitational acceleration, с - light velocity. The values marked with the subscript "0" are undisturbed parameters of considered medium and magnetic field H0. In our calculations we adopted isothermal atmosphere: = con s t . In this case the pressure and density are. p 0 (z),/> 0 (z)D е х р ( - * /Я ) , where H - scale height o f uniform atmosphere. The solution of the linearized equations for magnetogravity waves in finite conductivity space is the following dispersion equation: 121