Physics of auroral phenomena : proceedings of the 33rd Annual seminar, Apatity, 02 - 05 March, 2010 / [ed.: A.G. Yahnin, A. A. Mochalov]. - Апатиты : Издательство Кольского научного центра РАН, 2011. - 206 с. : ил.

“P hysics o f Auroral P henom ena“, Proc. XXXIII A nn ual Sem inar, Apatity, pp. 133 -1 3 6 , 2011 © Kola Science Centre, Russian Academy of Science, 2011 Polar Geophysical Institute NUM ER ICAL S IMULAT ION OF THE DYNAM IC S OF F INE -SCALE IRREGULARITIES IN THE NEAR -EARTH RAREFIED PLA SM A О. V. M ingalev, G. I. M ingaleva, M. N. Melnik, and V.S. M ingalev (Polar Geophysical Institute, Apatity, Russia, E-mail: mingalev@pgia.ru) Abstract. The time evolution of the magnetic field aligned fme-scale irregularities in the electron concentration, existing in the near-earth rarefied plasma, is studied with the help of the model simulation. A two-dimensional mathematical model, developed earlier in the Polar Geophysical Institute, is utilized to investigate the temporal history o f the sheetlike irregularity, created initially in the F-region ionosphere, during the period sufficient for the irregularity to decay completely. The utilized model is based on a numerical solution o f the Vlasov-Poisson system of equations, with the Vlasov equations describing the distribution functions of charged particles and the Poisson equation governing the self-consistent electric field. The system of equations is numerically solved applying a macroparticle method. Introduction Electron density irregularities are often observed in the Earth’s ionosphere. These irregularities have a wide range of spatial scales, ranging from a few Debye lengths to thousands of kilometers. The electron density depletions and increases inside irregularities can lie in the range from a few portions to some tens of percents (Fremouw et al, 1977; Martin and Aarons, 1977; Wong et a l, 1983; Kersley et a l, 1989; Pryse et a l, 1991). Not large-scale irregularities are predominately magnetic field aligned. Usually, there are three generic types of their structures: rods, wings, and sheets. Rods are isotropic in the plane perpendicular to the geomagnetic field. Wings and sheets are elongated not only along geomagnetic field but also in the perpendicular plane along a certain direction (Livingston et a l, 1982). Small-scale irregularities either are naturally present in the ionosphere, for example radio aurora (Sverdlov, 1982), or maybe artificially produced by high-power, high-frequency radio waves, pumped into the ionosphere (Wong et a l, 1983). The purpose of this paper is to investigate numerically the time evolution of the ionospheric plasma sheetlike irregularity whose thickness is much less than the mean free path of particles between successive collisions and commensurable with a Debye length. Numerical model At F-layer altitudes, the ionospheric plasma is a rarefied compound consisting of electrons and positive ions in the presence o f a strong, external, magnetic field. The studied irregularities are assumed to be geomagnetic field- aligned. In the vicinity of the irregularity, gradients of the plasma parameters in the longitudinal direction are supposed to be much less than those in a plane perpendicular to a magnetic field. Therefore, plasma parameters inside and beyond the irregularity may be considered as independent on the longitudinal coordinate. Hence, it is sufficient to consider a two dimensional flow of plasma in a plane perpendicular to a magnetic field line. The studied sheetlike irregularity has the perpendicular cross-section like a strait strip, with its cross-section sizes being much less than the mean free path of particles between successive collisions. To investigate the time evolution of the studied irregularity a two-dimensional mathematical model, developed earlier in the Polar Geophysical Institute, is utilized. In this model, kinetic processes in the plasma are simulated by using the Vlasov-Poisson system of equations, with the Vlasov equations describing the distribution functions of charged particles and the Poisson equation governing the self-consistent electric field. The Vlasov equations are numerically solved applying a macroparticle method. The Poisson equation is solved using a finite-difference method. More complete details of the utilized mathematical model may be found in the study of Mingalev et al. (2006). In the latter study, the mathematical model has been utilized for numerical simulation o f the behavior of small-scale rodlike irregularities existing in the magnetospheric plasma. In the present study, this mathematical model is used to investigate the time evolution o f fme-scale sheetlike irregularities, created initially in the F-region ionosphere, during the period sufficient for the irregularities to decay completely. Presentation and discussion of results The utilized mathematical model can describe the behavior of the near-earth plasma under various conditions. The results of calculations to be presented in this paper were obtained using the input parameters of the model typical for the nocturnal ionosphere at the level of 300 km. In particular, the value of the non-disturbed electron concentration (equal to the positive ion concentration) is 1011m '3 . The electron and ion temperatures are supposed to be equal to 1213 К and 930 K, respectively. The bulk flow velocities of electrons and positive ions are assumed to be zero. The value o f the magnetic field is 4.4-10 5 T. 133