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.

Numerical simulation o fthe dynamics offme-scale irregularities in the near-earth rarefied plasma 0 2 4 6 8 1 0 1 2 1 4 1 6 1 8 2 0 2 2 2 4 2 6 2 8 3 0 3 2 3 4 3 6 3 8 4 0 4 2 4 4 4 6 4 8 5 0 5 2 5 4 V > ' m » 5 .5 0 0 2 4 6 8 1 0 1 2 1 4 1 6 1 8 2 0 2 2 2 4 2 6 2 8 3 0 3 2 3 4 3 6 3 8 4 0 4 2 4 4 4 6 4 8 5 0 5 2 5 4 Fig. 2. The time variations of the electric field component, directed along the X axis, at the point, displaced from the center o f the simulation region in the X direction for a distance o f sixteen Debye lengths (l6 • X °De), (top panel) and of the normalized potential energy of the plasma filling up all simulation region, ( /) / W®in , (bottom panel). The time in units of the equilibrium period of Langmuir oscillations o f the electrons, 8 °pe, is shown on the horizontal axes. Simulation results, obtained for the first situation when the process started from the completely electrically neutral state, indicate that the spatial distributions of the electron and positive ion concentrations tend to retain a homogeneity and electrical neutrality of the plasma. However, short-scale non-regular fluctuations of the calculated parameters of the plasma arise near their initial values, with amplitudes of these fluctuations being very little. The presence o f the short-scale non-regular fluctuations of the calculated parameters of the plasma, referred to as a discrete noise, is due to the specific character of the applied macro-particle method, with the fluctuation amplitudes being conditioned by the number o f macro-particles used in the calculations. It should be emphasized that the amplitudes of the fluctuations, obtained for the first situation when process started from the completely electrically neutral state, characterize the accuracy of the applied numerical method that cannot be exceeded in following calculations. In the second situation, at the initial moment, the spatial distribution of the electron concentration contains an irregularity like a strait straight strip intersecting the simulation region across its center, with the spatial distribution of the positive ion concentration being homogeneous in all simulation region. Calculations were made for the case in which the initially created irregularity has the thickness o f 1 2 ^ , where X°De is the Debye length of the plasma. Inside this irregularity, a part o f electrons traveled from the internal strip, having the thickness of 6X°De, into the external strips, surrounding the internal strip. Calculations were performed for the case in which the relative decrease o f the electron concentration ( n0 - n e)/n 0, is equal to 0.2 in the internal strip at the initial moment. In other words, 20 percent of electrons were displaced from the center of the irregularity to its periphery. As a consequence of this displacement, an excess of positive charge appeared in the internal strip of the irregularity, while an excess of negative charge appeared in the strips surrounding it. The configuration of the initial irregularity in the plane perpendicular to the magnetic field is presented in Fig. la. Simulation results, obtained for the second situation, indicate that, after initial moment, the spatial distribution of the electron concentration changes essentially while the positive ion concentration is retained practically invariable. It turns out that the initially created irregularity vanishes completely during a short period, with the plasma becoming electrically neutral in all simulation region at the moment near to the equilibrium period of Langmuir oscillations of 135