Wave propagation and energy transport in the magnetic network of the Sun
Wave propagation and energy transport in the magnetic network of the Sun
复制标题
DOI：
10.1051/0004-6361/200912450
复制
发表时间：
2009-09
影响因子：
6.5
通讯作者：
G. Vigeesh;G. Vigeesh;S. Hasan;Oskar Steiner
中科院分区：
文献类型：
--
作者：
G. Vigeesh;G. Vigeesh;S. Hasan;Oskar Steiner
目标。我们调查波的传播和能量输运的磁性元素，这是小规模的磁通量集中在太阳上的磁网络的代表。这是Hasan等人早期工作的延续（2005，ApJ，631，1270）。在本调查的新功能包括定量评估的能量传输的各种模式和不同的场强，以及边界层厚度对波传播的影响。方法.本文对光球底部管轴上的气压比β = 0.4和1.7的强磁场和中等磁场下的磁通量集中进行了二维MHD数值模拟。波在管和周围介质中由下边界的横向脉冲运动激发。结果激发模式的性质取决于β的值。当快模式穿过β = 1轮廓时，在中等场情况下会发生模式转换。在强场的情况下，当波从通量集中的内部泄漏到周围介质时，快模式经历从主要是磁性到主要是声学的转换。我们还估计了声模和磁模中的能流，发现在强场情况下，垂直方向的声波通量在色球高度水平上达到空间平均的时间最大值，为10 6 erg cm-2 s-1的几倍。结论.我们的工作主要有两个方面的结论：第一，对于横向脉冲激励，强场的通量管/片比弱场的通量管/片更有效地向色球层提供声通量。然而，即使在强场情况下，声通量中的能量也不足以平衡网络中的色球辐射损失。第二，从磁通浓度和周围介质之间的界面处的声发射随着边界层的宽度而减小。
Aims. We investigate wave propagation and energy transport in magnetic elements, which are representatives of small scale magnetic flux concentrations in the magnetic network on the Sun. This is a continuation of earlier work by Hasan et al. (2005, ApJ, 631, 1270). The new features in the present investigation include a quantitative evaluation of the energy transport in the various modes and for different field strengths, as well as the effect of the boundary-layer thickness on wave propagation. Methods. We carry out 2D MHD numerical simulations of magnetic flux concentrations for strong and moderate magnetic fields for which β (the ratio of gas to magnetic pressure) on the tube axis at the photospheric base is 0.4 and 1.7, respectively. Waves are excited in the tube and ambient medium by a transverse impulsive motion of the lower boundary. Results. The nature of the modes excited depends on the value of β. Mode conversion occurs in the moderate field case when the fast mode crosses the β = 1 contour. In the strong field case the fast mode undergoes conversion from predominantly magnetic to predominantly acoustic when waves are leaking from the interior of the flux concentration to the ambient medium. We also estimate the energy fluxes in the acoustic and magnetic modes and find that in the strong field case, the vertically directed acoustic wave fluxes reach spatially averaged, temporal maximum values of a few times 10 6 erg cm −2 s −1 at chromospheric height levels. Conclusions. The main conclusions of our work are twofold: firstly, for transverse, impulsive excitation, flux tubes/sheets with strong fields are more efficient than those with weak fields in providing acoustic flux to the chromosphere. However, there is insufficient energy in the acoustic flux to balance the chromospheric radiative losses in the network, even for the strong field case. Secondly, the acoustic emission from the interface between the flux concentration and the ambient medium decreases with the width of the boundary layer.