Statistics – Computation
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmsm41a1440h&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #SM41A-1440
Statistics
Computation
0644 Numerical Methods, 0654 Plasmas, 2723 Magnetic Reconnection (7526, 7835), 7835 Magnetic Reconnection (2723, 7526)
Scientific paper
A series of computational research has been done to investigate coalescence of magnetic islands during magnetic reconnection by two-dimensional (2-D) particle-in-cell (PIC) code. In this research we have focused on structures in the magnetic O-point, in which a final coalescence occurs. Especially, the structures of out-of-plane magnetic field have been argued. A systematic survey has been done varying D0, m, BG and M, where D0 is the initial current sheet half thickness, m is the number of the initial small magnetic islands, BG is the initial value of out-of-plane magnetic field (Guide field), and M is the ion-to-electron mass ratio, respectively. In the initial setup, we chose one-dimensional Harris equilibrium with small perturbations used in the Geospace Environment Modeling (GEM). First, influence of m on structures of out-of-plane magnetic field is discussed. If m=2, quadrupole magnetic field comes out when two islands are merging into final bigger island. The direction of the magnetic field is opposite to the Hall magnetic field. Thus in this presentation, this coalescence is named "reversed Hall" type. In contrast, when m=4 and 8, the structure is quite different from that of "reversed Hall" type. When well-matured two magnetic islands (composed of 2 or 4 early small island) are coming closer to each other, flux of out-of-plane magnetic field between the islands is compressed to converge at the O- point, which is located almost the center of the final bigger magnetic island. Consequently, a strong out-of- plane magnetic field appears at the O-point. Therefore in this presentation, this type of coalescence is named "compression" type. The larger the parameter m is set, the stronger the compressive effect gets. Second, when D0 increases, the same tendency is found. The larger D0 is set, the more strongly magnetic flux is compressed. This is because the amount of conversion from magnetic energy into kinetic energy during reconnection is proportional to D0 and hence fiercer outflow pushes matured magnetic islands more strongly. Third, when BG is small, the field structure shows "reversed Hall" structure even though m ≥ 4. An understanding can be made that "greversed-Hall" field dominates over "compressed" field because there is little flux of out-of-plane magnetic field which would be compressed to converge at the O- point. Effectiveness of this idea will be discussed. Finally, effect of M on the structural change in coalescence found to be negligibly small. Additionally, temporal development from "reversed Hall" type to "compression" type also will be considered.
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