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arXiv 1106.5972astro-ph.SR
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冷等离子体向热日冕的喷射

Ejection of cool plasma into the hot corona

P. Zacharias, H. Peter, S. Bingert

摘要:

我们调查的过程,导致形成,喷射和下降的一个有限的等离子体喷射,观察到的数值实验中的日冕。通过量化的物理参数,如质量,速度和方向的等离子体喷射相对于磁场,我们提供了一个描述的性质,这种特殊的现象。在从色球层到低日冕的盒子中求解了含时三维磁流体动力学(3D MHD)方程。等离子体被加热的电流是通过场线编织作为光球运动的结果诱导。光谱的光学薄发射线在极紫外范围内的合成,和磁场线随时间的推移进行跟踪。在色球层上方强烈加热后,压力迅速增加,导致色球层上方低过渡区的流体动力爆炸。爆炸驱动等离子体,等离子体需要跟随磁场线。然后,喷射或多或少地沿着环状场线运动,最终落在太阳表面。喷射的速度在声速范围内,远低于阿尔芬速度。等离子体喷射基本上是一种流体动力学现象,而加热速率的上升具有磁性。光球层中的颗粒运动(偶然)导致了爆炸位置处磁场线的强烈编织,这反过来又导致了消散的强电流。未来的研究需要确定这一过程是否是小尺度上太阳上普遍存在的现象。太阳动力学观测台大气成像装置(AIA/SDO)提供的数据可能会提供相关信息。

英文摘要:

We investigate the processes that lead to the formation, ejection and fall of a confined plasma ejection that was observed in a numerical experiment of the solar corona. By quantifying physical parameters such as mass, velocity, and orientation of the plasma ejection relative to the magnetic field, we provide a description of the nature of this particular phenomenon. The time-dependent three-dimensional magnetohydrodynamic (3D MHD) equations are solved in a box extending from the chromosphere to the lower corona. The plasma is heated by currents that are induced through field line braiding as a consequence of photospheric motions. Spectra of optically thin emission lines in the extreme ultraviolet range are synthesized, and magnetic field lines are traced over time. Following strong heating just above the chromosphere, the pressure rapidly increases, leading to a hydrodynamic explosion above the upper chromosphere in the low transition region. The explosion drives the plasma, which needs to follow the magnetic field lines. The ejection is then moving more or less ballistically along the loop-like field lines and eventually drops down onto the surface of the Sun. The speed of the ejection is in the range of the sound speed, well below the Alfven velocity. The plasma ejection is basically a hydrodynamic phenomenon, whereas the rise of the heating rate is of magnetic nature. The granular motions in the photosphere lead (by chance) to a strong braiding of the magnetic field lines at the location of the explosion that in turn is causing strong currents which are dissipated. Future studies need to determine if this process is a ubiquitous phenomenon on the Sun on small scales. Data from the Atmospheric Imaging Assembly on the Solar Dynamics Observatory (AIA/SDO) might provide the relevant information.

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