Solar Flares: Magnetohydrodynamic Processes
Solar Flares: Magnetohydrodynamic Processes
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DOI：
10.12942/lrsp-2011-6
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发表时间：
2011-12
影响因子：
20.9
通讯作者：
K. Shibata;T. Magara
中科院分区：
文献类型：
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作者：
K. Shibata;T. Magara
本文概述了目前对太阳耀斑的理解，主要集中在磁流体动力学（MHD）过程负责产生耀斑。观测表明，耀斑是太阳大气中最具爆炸性的现象之一，在小时的时间尺度上释放出高达1032尔格的巨大能量。耀斑包括等离子体加热、物质抛射和产生高能粒子的粒子加速。产生耀斑的关键物理过程是：从太阳内部到太阳大气的磁场的出现（通量的出现），日冕中电流的局部增强（电流片的形成），以及电流的快速耗散（磁重联），导致冲击加热，质量抛射和粒子加速。当自由能以日冕电流（更准确地说是场向电流）的形式积累时，耀斑开始的演变是相当准静态的，而日冕电流的耗散进行得很快，产生各种影响低层大气（如色球层和光球层）的动态事件。耀斑表现出日冕电流的快速耗散，其理论模型是根据观测建立的，其中数值模拟被证明是再现耀斑随时间变化的非线性演化的有力工具。我们回顾了用于解释耀斑物理机制的模型，对上述关键过程进行了全面的解释。我们从耀斑的基本特性开始，然后进入耀斑的能量积累，释放和传输的细节，其中磁重联作为产生耀斑的中心引擎。
This paper outlines the current understanding of solar flares, mainly focused on magnetohydrodynamic (MHD) processes responsible for producing a flare. Observations show that flares are one of the most explosive phenomena in the atmosphere of the Sun, releasing a huge amount of energy up to about 1032 erg on the timescale of hours. Flares involve the heating of plasma, mass ejection, and particle acceleration that generates high-energy particles. The key physical processes for producing a flare are: the emergence of magnetic field from the solar interior to the solar atmosphere (flux emergence), local enhancement of electric current in the corona (formation of a current sheet), and rapid dissipation of electric current (magnetic reconnection) that causes shock heating, mass ejection, and particle acceleration. The evolution toward the onset of a flare is rather quasi-static when free energy is accumulated in the form of coronal electric current (field-aligned current, more precisely), while the dissipation of coronal current proceeds rapidly, producing various dynamic events that affect lower atmospheres such as the chromosphere and photosphere. Flares manifest such rapid dissipation of coronal current, and their theoretical modeling has been developed in accordance with observations, in which numerical simulations proved to be a strong tool reproducing the time-dependent, nonlinear evolution of a flare. We review the models proposed to explain the physical mechanism of flares, giving an comprehensive explanation of the key processes mentioned above. We start with basic properties of flares, then go into the details of energy build-up, release and transport in flares where magnetic reconnection works as the central engine to produce a flare.