Dynamics of plasmoids formed by the current sheet tearing
Dynamics of plasmoids formed by the current sheet tearing
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DOI：
10.1051/0004-6361:20078266
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发表时间：
2008
影响因子：
6.5
通讯作者：
M. Bárta;B. Vršnak;M. Karlický
中科院分区：
文献类型：
--
作者：
M. Bárta;B. Vršnak;M. Karlický
上下文。在软x射线和EUV范围内观察到的耀斑环上方的移动斑点状特征通常被解释为在耀斑相关的重连过程中由电流片撕裂形成的等离子体的特征。目标。为了分析等离子体的运动学和动力学，我们用数值方法研究了与耀斑相关的电流片的演化。目的是解释由各种观测技术记录的等离子体签名的广泛的运动特性的多样性。方法。我们从哈里斯型电流片开始对重联进行了二维电阻- mhd数值模拟。在确定等离子体后，我们跟踪它们的运动以确定基本的运动学参数（速度和加速度），并分析了相关的磁场拓扑结构。结果。模拟揭示了等离子体的各种各样的运动学/动力学特性——等离子体形成后可以向上、向下移动，甚至可以改变其传播方向。在环境阿尔芬速度范围内的最高速度是在向上传播的等离子体的情况下发现的。加速度由重新连接的磁场线的净磁场张力决定。向下传播的等离子体只达到环境阿尔芬速度的一小部分。它们在与低洼的耀斑环合并时强烈减速，此时会出现明显的能量释放峰，并激发环系统振荡。结论。所提出的结果定性和定量地解释了归因于电流片等离子体的各种观测特征的广谱运动特性。
Context. Moving blob-like features observed in the soft X-ray and EUV range above flare-loops are often interpreted as signatures of plasmoids formed by the current sheet tearing in the flare-associated reconnection process. Aims. We investigate the evolution of the flare-associated current sheet numerically in order to analyse the kinematics and dynamics of plasmoids. The goal is to explain the broad diversity of kinematical properties of the plasmoid signatures recorded by various observational techniques. Methods. We performed a 2-dimensional resistive-MHD numerical simulation of the reconnection starting from the Harris-type current sheet. After identifying the plasmoids, we followed their motion to determine basic kinematical parameters (velocity and acceleration), and we analysed the associated magnetic field topology. Results. The simulation reveals a broad variety of the kinematical/dynamical properties of plasmoids – after formation, a plasmoid can move upward, downward, or can even change its direction of propagation. The highest velocities, in the range of the ambient Alfven speed, are found in the case of upward propagating plasmoids. The acceleration is determined by the net magnetic field tension of the reconnected field lines. Downwardly propagating plasmoids achieve only a fraction of the ambient Alfven speed. They strongly decelerate during the coalescence with low-lying flare-loops, when distinct energy-release peaks occur and loop system oscillations are excited. Conclusions. The presented results explain, qualitatively and quantitatively, the broad spectrum of kinematical properties of various observational features attributed to the current-sheet plasmoids.