Magnetic flux emergence: a precursor of solar plasma expulsion
Magnetic flux emergence: a precursor of solar plasma expulsion
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DOI：
10.1051/0004-6361/201116956
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发表时间：
2012-01-01
影响因子：
6.5
通讯作者：
Hood, A. W.
中科院分区：
文献类型：
--
作者：
Archontis, V.;Hood, A. W.
目标。我们模拟了磁化等离子体从对流区顶部到下部日冕的出现。我们研究了新兴通量区域上方日冕通量绳的爆发。我们进行了三维数值实验，其中的时间相关的和电阻性的MHD方程求解自洽，使用Lare 3D代码。一个亚光球层的磁通量管从对流不稳定层上升到太阳表面，然后形成一个新的通量绳并喷发到日冕中。首先，我们研究了电晕是无场的情况。新兴领域的扩展形成了一个信封鞘，包围新形成的磁通绳。爆发绳受到包络场的限制。喷发是由气体压力梯度和在新兴通量区域内重新连接的场线张力驱动的。新兴领域的初始扭曲量和被提升的稠密等离子体，决定了爆发绳的高度-时间曲线。其次，我们研究了在太阳上层大气中出现到预先存在的磁场中的情况。在实验中使用了各种不同的环境场配置。新出现的场和先存在的场之间的外部重联可能导致从相互作用的场中移除足够的通量并完全喷射通量绳。结果表明，相互作用的通量系统的相对接触角和它们的场强是最终影响绳状喷发到更高的太阳大气的演化的关键参数。一个重要的结果是，对于任何有利于重联的接触角，当环境场相对较强时，喷射喷发发生得更早。在许多情况下，喷发的等离子体采用S形构型。S形结构在绳快速喷发期间加速。在绳索的上升运动期间，通过外部和内部的场线重连来增强加速度。一个关键的结果是，在重联有利的情况下，磁通绳经历喷射喷发时，包络通量减少（由于外部重联去除）低于喷发磁通绳。如果包络通量保持高于爆发通量，则磁通绳保持被包络场限制。
Aims. We model the emergence of magnetized plasma from the top of the convection zone to the lower corona. We investigate the eruption of coronal flux ropes above emerging flux regions.Methods. We performed three-dimensional numerical experiments in which the time-dependent and resistive equations of MHD are solved self-consistently, using the Lare3D code.Results. A subphotospheric magnetic flux tube rises from the convectively unstable layer into the solar surface, followed by the formation and eruption of a new flux rope into the corona. Firstly, we examined the case where the corona is field-free. The expansion of the emerging field forms an envelope sheath that surrounds the newly formed flux rope. The erupting ropes are confined by the envelope field. The eruptions are driven by the gradient of the gas pressure and the tension of fieldlines that reconnect within the emerging flux region. The amount of the initial twist of the emerging field and the dense plasma that is lifted up, determine the height-time profile of the erupting ropes. Secondly, we examined the case of emergence into a pre-existing magnetic field in the upper solar atmosphere. A variety of different ambient field configurations was used in the experiments. External reconnection between the emerging and the pre-existing field may result in the removal of sufficient flux from the interacting fields and the full ejection of the flux ropes.Conclusions. The results indicate that the relative contact angle of the interacting flux systems and their field strengths are crucial parameters that ultimately affect the evolution of the eruption of the rope into the higher solar atmosphere. One important result is that for any contact angle that favors reconnection, ejective eruptions occur earlier when the ambient field is relatively strong. In many cases, the erupting plasma adopts an S-like configuration. The sigmoidal structure accelerates during the fast eruption of the rope. The acceleration is enhanced by the external and internal reconnection of fieldlines during the rising motion of the rope. A key result is that in the reconnection-favored cases, the flux ropes experience ejective eruptions when the envelope flux is reduced (owing to removal by external reconnection) below that of the erupting flux rope. If the envelope flux stays higher than the erupting flux, the magnetic flux rope remains confined by the envelope field.