Convection-driven emergence of small-scale magnetic fields and their role in coronal heating and solar wind acceleration
Convection-driven emergence of small-scale magnetic fields and their role in coronal heating and solar wind acceleration
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DOI：
10.1086/589150
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发表时间：
2008-05-20
影响因子：
7.9
通讯作者：
Weiss, N. O.
中科院分区：
文献类型：
--
作者：
Isobe, H.;Proctor, M. R. E.;Weiss, N. O.
日野号上的太阳光学望远镜（SOT）最近的观测显示，平均而言，太阳表面覆盖着小规模的水平磁场。在平静的太阳和斑区，经常出现颗粒尺度的水平磁通量。在这封信中，我们提出了磁流体动力学模拟的结果，覆盖上对流区和日冕。研究发现，即使初始磁场是均匀垂直的，对流区也会产生无序磁场。光球磁场表现为集中在粒间带的强垂直场和相对较弱的水平场。偶尔，具有大磁通量的碎片被向上的对流气流驱动到光球之上。这些特征与SOT观测结果一致。此外，在颗粒尺度上出现的模拟通量随着色球中垂直磁浓度的增加而发生磁重联。这些重联事件加热了当地的等离子体，并发射高频波，传播到日冕中。这种小规模水平场与垂直通量之间的相互作用可能在日冕加热和风在太阳和恒星中的加速中起重要作用。
Recent observations by the Solar Optical Telescope (SOT) on board Hinode have revealed that the surface of the Sun is, on average, covered with small-scale horizontal magnetic fields. Frequent emergence of horizontal magnetic flux on a granular scale is found in the quiet Sun and in plage regions. In this Letter we present the results of magnetohydrodynamic simulations that cover the upper convection zone and the corona. It is found that, even when the initial magnetic field is uniform and vertical, a disordered magnetic field is produced in the convection zone. The photospheric magnetic field is then characterized by strong vertical fields concentrated in the intergranular lanes and relatively weak, horizontal fields both in the granules and in the intergranular lanes. Occasionally, fragments with large magnetic fluxes are driven above the photosphere by the upward convective flows. These characteristics are consistent with the SOT observations. Moreover, the simulated flux emerging on a granular scale undergoes magnetic reconnection with the expanding vertical magnetic concentrations in the chromosphere. These reconnection events heat the local plasma and emit high-frequency waves that propagate into the corona. Such an interplay between the small-scale horizontal fields and the vertical flux may play an important role in coronal heating and wind acceleration in the Sun and stars.