在有和没有磁重联的日冕和太阳风中磁通量绳的灾难性爆发
Catastrophic eruption of magnetic flux rope in the corona and solar wind with and without magnetic reconnection
摘要：
一般认为，日冕中积累的磁自由能是太阳爆发（如日冕物质抛射（CME））的主要能量来源。在CME的磁绳突变模型框架下，能量的突然释放既可能是由于系统的全局磁拓扑不稳定性引起的理想磁流体动力学（MHD）突变，也可能是由于系统中已存在或快速发展的电流片之间的快速磁重联。这两种方式的磁能释放被认为是重要的日冕物质抛射动力学。为了解开他们的贡献，我们在日冕和太阳风中构建了一个通量绳突变模型，并比较了不同的情况下，我们要么禁止或允许磁重联发生在爆发期间快速增长的电流片。结果表明，以理想的MHD灾变作为唯一的磁能释放过程，可以产生CME，甚至是快的CME。然而，磁重联发生后，喷发速度可显著提高。此外，当增加背景磁场的强度时，可以观察到从缓慢到快速喷发的平滑过渡，这仅仅是因为在更强的磁场中，在喷发过程中，灾难点处有更多的自由磁能可以释放。这表明，快速和慢速的日冕物质抛射可能具有相同的驱动机制。
英文摘要：
It is generally believed that the magnetic free energy accumulated in the corona serves as a main energy source for solar explosions such as coronal mass ejections (CMEs). In the framework of the flux rope catastrophe model for CMEs, the energy may be abruptly released either by an ideal magnetohydrodynamic (MHD) catastrophe, which belongs to a global magnetic topological instability of the system, or by a fast magnetic reconnection across preexisting or rapidly-developing electric current sheets. Both ways of magnetic energy release are thought to be important to CME dynamics. To disentangle their contributions, we construct a flux rope catastrophe model in the corona and solar wind and compare different cases in which we either prohibit or allow magnetic reconnection to take place across rapidly-growing current sheets during the eruption. It is demonstrated that CMEs, even fast ones, can be produced taking the ideal MHD catastrophe as the only process of magnetic energy release. Nevertheless, the eruptive speed can be significantly enhanced after magnetic reconnection sets in. In addition, a smooth transition from slow to fast eruptions is observed when increasing the strength of the background magnetic field, simply because in a stronger field there is more free magnetic energy at the catastrophic point available to be released during an eruption. This suggests that fast and slow CMEs may have an identical driving mechanism.
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