A new kind of magnetohydrodynamic instability and waves are analyzed for a current sheet in the presence of a small normal magnetic field component varying along the sheet. These waves and instability are related to existence of two gradients of the tangential and normal magnetic field components along the normal and tangential directions with respect to the current sheet. The current sheet can be stable or unstable if the multiplication of two magnetic gradients is positive or negative. In the stable region, the kink-like wave mode is interpreted as so called flapping waves observed in the Earth's magnetotail current sheet. The kink wave group velocity estimated for the Earth's current sheet is of the order of a few tens kilometers per second. This is in good agreement with the observations of the flapping motions of the magnetotail current sheet.
Kink-like flapping motions of current sheets are commonly observed in the magnetotail. Such oscillations have periods of a few minutes down to a few seconds and they propagate toward the flanks of the plasma sheet. Here, we report a short-period ($T\approx25$ s) flapping event of a thin current sheet observed by the Magnetospheric Multiscale (MMS) spacecraft in the dusk-side plasma sheet following a fast Earthward plasma flow. We characterize the flapping structure using the multi-spacecraft spatiotemporal derivative and timing methods, and we find that the wave-like structure is propagating a…
Dynamic mitigation is presented for filamentation instability and magnetic reconnection in a plasm driven by a wobbling electron sheet current. The wobbling current introduces an oscillating perturbation and smooths the perturbation. The sheet current creates an anti-parallel magnetic field in plasma. The initial small perturbation induces the electron beam filamentation and the magnetic reconnection. When the wobbling or oscillation motion is added to the sheet electron beam along the sheet current surface, the perturbation phase is mixed and consequently the instability growth is delayed rem…
Magnetic reconnection is a fundamental physical process converting magnetic energy into not only plasma energy but also particle energy in various astrophysical phenomena. In this letter, we show a unique dataset of a solar flare where various plasmoids were formed by a continually stretched current sheet. EUV images captured reconnection inflows, outflows, and particularly the recurring plasma blobs (plasmoids). X-ray images reveal nonthermal emission sources at the lower end of the current sheet, presumably as large plasmoids with a sufficiently amount of energetic electrons trapped in. In t…
One of the most important problems of magnetotail dynamics is the substorm onset and the related instability of the magneotail current sheet. Since the simplest 2D current sheet configuration with monotonic $B_z$ was proven to be stable to the tearing mode, the focus of the instability investigation moved to more specific configurations, e.g. kinetic current sheets with strong transient ion currents and current sheets with non-monotonic $B_z$ (local $B_z$ minima or/and peaks). Stability of the latter current sheet configuration has been studied both within kinetic and fluid approaches, whereas…
Development of Tearing Instability in a Current Sheet Forming by Sheared Incompressible Flow
高伦德奎斯特数等离子体中的Sweet-Parker电流片对撕裂不稳定，这表明它们不会在物理系统中形成。因此，理解磁重联需要研究电流片形成时的稳定性。由于剪切，亚阿尔夫文不可压缩流使片变窄，因此可能发生形成。标准撕裂理论（Furth等，1963; Coppi等，1976; Rutherford，1973）不能直接应用于这种成形薄板，原因有二：第一，因为流动引入了标准计算中不存在的项;第二，因为变化的平衡引入了标准计算中常数项的时间依赖性，使本征值问题的公式化复杂化。本文采用标准的撕裂模式分析，以面对这些挑战。在初始阶段，当任何扰动主要由理想MHD支配时，坐标变换揭示了流动压缩和拉伸扰动。多尺度公式描述了线性撕裂模理论（Furth et al. 1963; Coppi et al. 1976）如何应用于流动下的平衡变化，表明通过使标准尺度依赖于时间，流动仅隐含地影响可分离的指数增长。在非线性卢瑟福阶段，坐标变换表明，标准理论可以通过添加到稳态速率的时间依赖性和一个额外的项，由于加强平衡磁场。总的来说，这种理解支持使用无流动的缩放与轻微的修改，以研究在成形片材撕裂。
The presence of current sheet instabilities, such as the tearing mode instability, are needed to account for the observed rate of energy release in solar flares. Insights into these current sheet dynamics can be revealed by the behaviour of flare ribbon substructure, as magnetic reconnection accelerates particles down newly reconnected field lines into the chromosphere to mark the flare footpoints. Behaviour in the ribbons can therefore be used to probe processes occurring in the current sheet. In this study, we use high-cadence (1.7 s) IRIS Slit Jaw Imager observations to probe for the growth…
The magnetotail current sheet configuration determines magnetic reconnection properties that control the substorm onset, one of the most energetic phenomena in the Earth's magnetosphere. The quiet-time current sheet is often approximated as a two-dimensional (2D) magnetic field configuration balanced by isotropic plasma pressure gradients. However, reconnection onset is preceded by the current sheet thinning and the formation of a nearly one-dimensional (1D) magnetic field configuration. In this study, using particle-in-cell simulations, we investigate the force balance of such thin current sh…
Resistive instabilities of current sheets in stratified plasmas with a gravitational field
Institute for Fusion Studies, Department of Physics, The University of Texas at Austin（德克萨斯大学奥斯汀分校物理系聚变研究所）；Department of Physics, Faculty of Science, Assiut University（阿西尤特大学理学院物理系）
In flare-relevant current sheets, tearing instability may trigger explosive reconnection and plasmoid formation. We explore how the thermal and tearing modes reinforce each other in the fragmentation of a current sheet in the solar corona through an explosive reconnection process, characterized by the formation of plasmoids which interact and trap condensing plasma. We use a resistive magnetohydrodynamic (MHD) simulation of a 2D current layer, incorporating the non-adiabatic effects of optically thin radiative energy loss and background heating using \texttt{MPI-AMRVAC}. Our parametric survey …
The tearing mode instability is one important mechanism that may explain the triggering of fast magnetic reconnection in astrophysical plasmas such as the solar corona and the Earth's magnetosphere. In this paper, the linear stability analysis of the tearing mode is carried out for a current sheet in the presence of a guide field, including the Hall effect. We show that the presence of a strong guide field does not modify the most unstable mode in the two-dimensional wave vector space orthogonal to the current gradient direction, which remains the fastest growing parallel mode. With the Hall e…
