Physics – Plasma Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsm53a..07s&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #SM53A-07
Physics
Plasma Physics
[2736] Magnetospheric Physics / Magnetosphere/Ionosphere Interactions, [2744] Magnetospheric Physics / Magnetotail, [7839] Space Plasma Physics / Nonlinear Phenomena
Scientific paper
Ample evidence suggests that thin current sheets, forming in the magnetotail during substorm growth phases, play a key role in magnetotail dynamics. Therefore, it is important to identify the conditions under which slow evolution of the magnetotail leads to the formation of thin current sheets, preferably, when the initial states are smooth. Pertinent results obtained from particle simulation and kinetic theory, applied to a simplified model with one spatial and three velocity dimensions, are discussed. The gyrotropic current densities of ions and electrons, obtained in the formal limit of vanishing particle mass provide appropriate reference levels for the current densities. Deviations from these levels, defining the nongyrotropic current densities, are of particular interest in the context of thin current sheets. For configurations with antisymmetric magnetic fields, a general analytical expression for spatially integrated nongyrotropic currents is presented in terms of properties of the initial state and a ‘compression factor’ measuring the amount of external driving. For several examples simulation results provide details about the spatial structure. Double-peaked and triple-peaked current densities as well as triaxial pressure anisotropy are among the observed features. In some cases a U-shaped electric potential perpendicular to the magnetic field arises. As suggested earlier, the projection of current sheet potentials into the near-Earth magnetosphere and the accompanying field-aligned currents would lead to a relevant form of magnetospheric-auroral connection. This projection would provide the magnetospheric input into existing modeling of quiet auroral arcs, where the role of the magnetosphere is left open. Preliminary quantitative estimates based on our results seem promising. Should this scheme be confirmed by further studies, it would establish a causal chain beginning at the solar wind driving the growth phase evolution, proceeding through current sheet formation in the tail, and ending by the formation of (quiet) auroral arcs in the high latitude atmosphere. This work was supported by NASA’s MMS mission. One of us (KS) gratefully acknowledges the kind support he received from the Goddard Space Flight Center.
Birn Joachim
Hesse Matthias
Schindler Karl
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