Nonlinear equilibrium structure of thin currents sheets: influence of electron pressure anisotropy

Abstract

Abstract. Thin current sheets represent important and puzzling sites of magnetic energy storage and subsequent fast release. Such structures are observed in planetary magnetospheres, solar atmosphere and are expected to be widespread in nature. The thin current sheet structure resembles a collapsing MHD solution with a plane singularity. Being potential sites of effective energy accumulation, these structures have received a good deal of attention during the last decade, especially after the launch of the multiprobe CLUS-TER mission which is capable of resolving their 3D features. Many theoretical models of thin current sheet dynamics, including the well-known current sheet bifurcation, have been developed recently. A self-consistent 1D analytical model of thin current sheets in which the tension of the magnetic field lines is balanced by the ion inertia rather than by the plasma pressure gradients was developed earlier. The influence of the anisotropic electron population and of the corresponding electrostatic field that acts to restore quasi-neutrality of the plasma is taken into account. It is assumed that the electron motion is fluid-like in the direction perpendicular to the magnetic field and fast enough to support quasi-equilibrium Boltzmann distribution along the field lines. Electrostatic effects lead to an interesting feature of the current density profile inside the current sheet, i.e. a narrow sharp peak of electron current in the very center of the sheet due to fast curvature drift of the particles in this region. The corresponding magnetic field profile becomes much steeper near the neutral plane although the total cross-tail current is in all cases dominated by the ion contribution. The dependence of electrostatic effects on the ion to electron temperature ratio, the curvature of the magnetic field lines, and the average electron magnetic moment is also analyzed. The implications of these effects on the fine structure of thin current sheets and their potential impact on substorm dynamics are presented.

Circulation of Heavy Ions and Their Dynamical Effects in the Magnetosphere: Recent Observations and Models

“…Ashour-Abdalla et al 1994;Hoshino et al 1996;). In the frame of the quasiadiabatic model (Zelenyi et al 2004b), this feature was explained by different partial contributions from electron curvature currents and transient and quasi-trapped ions, depending upon parameters of the field configuration and plasma streams in TCS Malova et al 2013). Generally, the presence of O + ions in the magnetotail leads to thickening of TCS as is illustrated in Fig.…”

Thin embedded current sheets: Cluster observations of ion kinetic structure and analytical models

“…Using the CS model by Zelenyi et al (2004), which provides an essential embedding, Artemyev et al (2008a) have been able to reach an impressing agreement between theoretical and observed current density profiles. However, plasma density and temperature, required by the model to fit the experimental profiles were often rather different (by 30%) from the measured ones.…”

“…The third model we use is a thin anisotropic CS model (Zelenyi et al, 2004) with electron component (hereafter referred to as TACS). It can be also considered as a generalization of some earlier models of thin CS (Eastwood, 1972;Kropotkin and Domrin, 1996).…”

“…Another unexpected feature was abundance of strongly tilted (in the YZ GSM plane) sheets with rather variable profiles (Sergeev et al, 2004;Petrukovich et al, 2006), which most likely represent nonstationary structures (Malova et al, 2007;Petrukovich et al, 2008;Zelenyi et al, 2009;Erkaev et al, 2009) and often cannot be explained by motion of the sheet as a whole. A variety of TCS models available now is also quite wide (Kropotkin and Domrin, 1996;Schindler and Birn, 2002;Sitnov et al, 2006;Zelenyi et al, 2004;Yoon and Lui, 2004) (see Sect. 6 for details).…”

Hysteresis-controlled instability waves in a scale-free driven current sheet model

“…Zelenyi et al, 2002Zelenyi et al, , 2004Sitnov et al, 2004 and references therein). In additional to these findings, our analysis strongly suggests that under certain conditions, thin current sheets can also move in a form of solitary self-supporting waves giving rise to complex scale-invariant spatial patterns of activity in vast portions of the magnetotail.…”