MHD Modelling of Coronal Loops: Injection of High-Speed Chromospheric Flows
MHD Modelling of Coronal Loops: Injection of High-Speed Chromospheric Flows
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日冕环的 MHD 建模：高速色球流的注入
DOI：
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发表时间：
2014
期刊：
影响因子：
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通讯作者：
J. Klimchuk
中科院分区：
文献类型：
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作者：
A. Petralia;F. Reale;S. Orlando;J. Klimchuk
上下文观测结果显示，色球II型针状体与极紫外波段观测到的日冕中明亮的向上移动的锋面之间存在对应关系。然而，理论上的考虑表明，这些流动可能不是日冕磁环的主要热源。目标。我们调查的传播高速色球流到日冕磁通管和可能产生的EUV波段的发射。方法.我们模拟了一个致密的10 - 4 K色球喷流向上沿着一个日冕环的传播通过一个二维圆柱MHD模型，包括重力，辐射损失，热传导，磁感应。喷流在一个完整的大气层中传播，包括色球层和一个稀薄的冷（10.8 MK）日冕，通过陡峭的过渡区连接。在我们的参考模型中，喷流的初始速度为70 km s −1，初始密度为10 11 cm −3，周围的均匀磁场为10 G。我们还探讨了其他值的喷流速度和密度在一维和不同的磁场值在二维，以及喷流传播在一个更热（1.5 MK）的背景环。结果虽然喷流的初始速度不允许它到达环的顶点，但在它前面会形成一个热激波阵面，并行进到环的另一端。激波阵面压缩日冕等离子体并将其加热到约106 K.因此，在SDO/AIA使命的171 A通道中可以看到一个明亮的移动波前。这一结果一般适用于所有其他探索的情况下，除了在较热的环路中的传播。结论.对于一个冷的，低密度的初始日冕环，冲击后的等离子体前面向上的色球流可能解释至少部分的II型针状体和EUV辐射过剩之间的观测对应关系。
Context. Observations reveal a correspondence between chromospheric type II spicules and bright upward-moving fronts in the corona observed in the extreme-ultraviolet (EUV) band. However, theoretical considerations suggest that these flows are probably not the main source of heating in coronal magnetic loops. Aims. We investigate the propagation of high-speed chromospheric flows into coronal magnetic flux tubes and the possible production of emission in the EUV band. Methods. We simulated the propagation of a dense 10 4 K chromospheric jet upward along a coronal loop by means of a 2D cylindrical MHD model that includes gravity, radiative losses, thermal conduction, and magnetic induction. The jet propagates in a complete atmosphere including the chromosphere and a tenuous cool (∼0.8 MK) corona, linked through a steep transition region. In our reference model, the jet initial speed is 70 km s −1 , its initial density is 10 11 cm −3 , and the ambient uniform magnetic field is 10 G. We also explored other values of jet speed and density in 1D and different magnetic field values in 2D, as well as the jet propagation in a hotter (∼1.5 MK) background loop. Results. While the initial speed of the jet does not allow it to reach the loop apex, a hot shock-front develops ahead of it and travels to the other extreme of the loop. The shock front compresses the coronal plasma and heats it to about 10 6 K. As a result, a bright moving front becomes visible in the 171 A channel of the SDO/AIA mission. This result generally applies to all the other explored cases, except for the propagation in the hotter loop. Conclusions. For a cool, low-density initial coronal loop, the post-shock plasma ahead of upward chromospheric flows might explain at least part of the observed correspondence between type II spicules and EUV emission excess.