A model for the emergence of a twisted magnetic flux tube
A model for the emergence of a twisted magnetic flux tube
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DOI：
10.1086/317846
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发表时间：
2000-12-20
影响因子：
4.9
通讯作者：
Welsch, BT
中科院分区：
文献类型：
--
作者：
Longcope, DW;Welsch, BT
观察表明，有源区磁通管经常以扭曲状态出现，并且所形成的有源区具有与形成它的磁通管相同意义的磁螺旋度。已经为具有螺旋性的日冕磁场和具有扭曲的通量管开发了单独的理论模型。在这里，我们提出了一个动力学模型，将扭曲的亚光球通量管连接到无力日冕场。通过该模型，可以探索日冕中通量管的出现及其对日冕场和亚光球通量管的影响。特别是，该模型表明，只有扭曲磁通管承载的电流的一小部分会进入电晕。由于这种“不匹配”，在阿尔文出现的瞬间，扭转波沿着通量管向下发射。随着通量管继续出现，冠状场的螺旋度由于足点的旋转而增加。我们的模型预测，旋转水平将取决于通量出现的速度。在此瞬态期之后，有源区的螺旋度将反映其母管中的扭曲。
Observations have shown that active region flux tubes often emerge in a twisted state and that the active region formed has magnetic helicity of the same sense as the flux tube that forms it. Separate theoretical models have been developed for coronal magnetic fields with helicity and for flux tubes with twist. Here we present a dynamical model that connects a twisted subphotospheric flux tube to a force-free coronal field. With this model it is possible to explore the emergence of a flux tube into the corona and its effect on both the coronal field and the subphotospheric flux tube. In particular, the model shows that only a fraction of the current carried by the twisted flux tube will pass into the corona. As a consequence of this "mismatch," II a torsional wave is launched downward along the flux tube at the Alfven instant of emergence. As the flux tube continues to emerge, the helicity of the coronal field increases owing to rotation of the footpoints. Our model predicts that the level of rotation will depend upon the rapidity of flux emergence. After this transient period the helicity of the active region will reflect the twist in its parent tube.