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.

О. У. Mingalev at al. the electrons. Figure lb illustrates this condition. Further calculations indicate that the changes in the electron concentration are continued and, after a short period, the irregularity arises again to a moment o f about (2.2 - 2.3) вре . This fact is illustrated by Fig. lc. It can be seen that the recovered irregularity almost completely coincides with the initial one presented in Fig. la. Later, the cycle of vanishing and recovering of the irregularity is repeated again and again (Fig. Id). Thus, the time evolution of the initially created irregularity is accompanied by periodic vibrations. After the first vibration, the period of these vibrations is equal to the equilibrium period of Langmuir oscillations of electrons. In the course o f time, the amplitudes o f the vibrations of the electron concentration and other parameters decrease smoothly, with the irregularity decaying little by little. One of the parameters, characterizing the plasma, is a normalized potential energy of the plasma, filling in a spatial volume V, which may be defined as Wpot(t)IW^in , where Wpot (t) is the potential energy of the plasma, and W°in is the initial kinetic energy o f all particles filling in the volume V. Results o f simulation indicate that the normalized potential energy o f the plasma can fluctuate. Examples o f fluctuating parameters of the plasma are presented in Fig.2. Results of simulation indicate that, during the time interval o f about 35 periods of Langmuir oscillations of electrons, the considered irregularity lost almost completely its initial structure, was diffused, and decayed. It is of interest to note that, in the process of evolution, additional almost symmetrical alternate strips with an excess of charge of different sign begin to appear around the initial irregularity (Fig. Id). In the course o f time, these additional strips begin to fill up all simulation regions. It can be noticed that we have made calculations for other cases in which the irregularity thickness and the initial relative decrease of the electron concentration inside the central strip of the irregularity were different. In essence, simulation results for these cases turn out to be qualitatively analogous to the results, obtained for the basic case, described above in this study, and presented in Figs. 1-2. Conclusions Results of numerical simulations were presented of the dynamics of the magnetic field aligned fine-scale irregularities in the electron concentration, created initially in the F-region ionosphere. The irregularities like sheet were considered which have the initial thickness equal to a few Debye lengths. The results were obtained by applying the earlier developed two-dimensional mathematical model, based on numerical solving the Vlasov- Poisson system of equations by using the macroparticle method. The simulation results indicated that, in the course of time, the irregularity decays accomplishing periodic damped vibrations, with the period of these vibrations being equal to the equilibrium period of Langmuir oscillations of electrons. The time interval of about 35 periods of Langmuir oscillations of electrons was sufficient for the irregularity to decay completely. A cknow ledgm en ts. This work was partially supported by the Division of the Physical Sciences of the RAS through the program “Plasma processes in the solar system” and by the RFBR grant 10-01-00451. References Fremouw, E.J., C.L. Rino, R.C. Livingston, and M.C. Cousins, A persistent subauroral scintillations enhancement observed in Alaska, Geophys. Res. Lett, 4, 539-542, 1977. Kersley, L , C.D. Russell, and S.E. Pryse, Scintillation and EISCAT investigations of gradient-drift irregularities in the high latitude ionosphere, J. Atmos. Terr. Phys, 51, 241-247, 1989. Livingston, R .C , C.L. Rino, J. Owen, and R.T. Tsunoda, The anisotropy o f high-latitude nighttime F region irregularities, J. Geophys. R es, 87,10519-10526, 1982. Martin, E. and J. Aarons, F layer scintillations and the aurora, J. Geophys. R e s, 82, 2717-2722, 1977. Mingalev O.V., I.V. Mingalev, and V.S. Mingalev, Two-dimensional numerical simulation of dynamics of small- scale irregularities in the near-Earth plasma, Cosmic Research, 44, 398-408, 2006. Pryse, S.E , L. Kersley, and C.D. Russell, Scintillation near the F layer trough over northern Europe, Radio Sci 26 1105-1114,1991. Sverdlov, Yu. L , Morphology of radio aurora, Nauka, Leningrad, 1982 (in Russian). Wong, A .Y , J. Santoru, C. Darrow, L. Wang, and J.G. Roederer, Ionospheric cavitons and related nonlinear phenomena, Radio Sci, 18, 815-830, 1983. 136