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.

中文翻译：

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太阳耀斑：磁流体动力学过程

本文概述了当前对太阳耀斑的理解，主要集中在负责产生耀斑的磁流体动力学（MHD）过程中。观测表明，耀斑是太阳大气中最爆炸的现象之一，释放出的能量高达10 ³²耗时数小时。耀斑涉及等离子体的加热，物质喷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（助焊剂的出现），电晕中电流的局部增强（电流片的形成）以及电流的快速耗散（磁性重新连接）会导致电击加热，质量弹出和粒子加速。当自由能量以日冕电流（更准确地说是场对准电流）的形式积累时，朝着爆发的演变相当准静态，而日冕电流的耗散迅速进行，产生各种动态事件，影响色球层和光球层等低层大气。耀斑表现出如此快速的日冕电流消散，并且根据观察结果发展了它们的理论模型，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强大工具。我们回顾了提出的解释火炬物理机制的模型，并对上述关键过程进行了全面的解释。我们从火炬的基本特性开始，然后深入研究火炬中能量积累，释放和运输的细节，其中磁重连作为产生火炬的中央引擎。其中，数值模拟被证明是再现火炬随时间变化的非线性演化的强大工具。我们回顾了提出的解释火炬物理机制的模型，并对上述关键过程进行了全面的解释。我们从火炬的基本特性开始，然后深入研究火炬中能量积累，释放和运输的细节，其中磁重连作为产生火炬的中央引擎。其中，数值模拟被证明是再现火炬随时间变化的非线性演化的强大工具。我们回顾了提出的解释火炬物理机制的模型，并对上述关键过程进行了全面的解释。我们从火炬的基本属性开始，然后深入探讨火炬中能量积累，释放和运输的细节，其中磁重连作为产生火炬的中央引擎。