THE SOLAR DYNAMO AND EMERGING FLUX
THE SOLAR DYNAMO AND EMERGING FLUX
复制标题
太阳能发电机和新兴通量
DOI：
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发表时间：
1999
期刊：
影响因子：
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通讯作者：
A. Pevtsov
中科院分区：
文献类型：
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作者：
G. Fisher;Yuhong Fan;D. Longcope;M. Linton;A. Pevtsov
太阳上最大的磁通量集中发生在活动区域。本文根据磁通管的动力学研究了活跃区的性质，这些磁通管是从太阳对流区底部出现的，太阳周期发电机被认为是在那里工作的，到光球。采用“薄磁通管”近似和MHD模拟计算了磁通管的动力学。通过对活动区的出现和演化过程的模拟，与已知的活动区的观测结果进行比较，得出了以下结论：(1)对流区底部的磁场被限制在一个近似环面几何形状，磁场强度在这个范围内。3-1 0/ 10 4 G.对流区底部环面场的纬度分布或多或少地反映了观测到的活动纬度；当它们出现时，活跃区域并没有大规模向极地漂移。从对流区底部到地表出现活动区域的时间尺度通常为2 - 4个月。活跃区分布的赤道缺口有两种可能的成因；如果环面场强接近105g，则是由于在低纬度处缺乏平衡解；如果接近3104g，则可能是由于出现时适度的向极地漂移。(2)活动区的倾斜主要是由于科里奥利力作用于上升通量环的发散流。倾斜中的色散主要是由通量管在内部上升时对流运动引起的抖振引起的。(3)科里奥利力还使有源区磁通管形状向以下（即反旋转）方向弯曲，导致与有源区的前侧相比，后侧的支腿更陡。当活跃区域通过光球出现时，这导致与后面的斑点相比，领先的斑点从磁中性线分离得更快。这种弯曲运动也导致中性线更接近下面的磁极性。(4)由于“动态断裂”，活动区域在出现后表现为运动学行为，这是由于流体静力平衡方程在通量环出现后缺乏解而发生的。这可以解释为什么活动区域一旦出现就会衰减，以及为什么活动区域的平流-扩散描述在出现后效果很好。较小的磁通管可能经历“磁通管爆炸”，这是一个类似的过程，并为不断出现的小规模磁场提供了来源。(5)北半球最活跃的地区有负磁扭转的轻微趋势和国家大气研究中心是由美国国家科学基金会资助的。
The largest concentrations of magnetic flux on the Sun occur in active regions. In this paper, the properties of active regions are investigated in terms of the dynamics of magnetic flux tubes which emerge from the base of the solar convection zone, where the solar cycle dynamo is believed to operate, to the photosphere. Flux tube dynamics are computed using the 'thin flux tube' approxi- mation, and by using MHD simulation. Simulations of active region emergence and evolution, when compared with the known observed properties of active regions, have yielded the following results: (1) The magnetic field at the base of the convection zone is confined to an approximately toroidal geometry with a field strength in the range . 3-1 0/ 10 4 G. The latitude distribution of the toroidal field at the base of the convection zone is more or less mirrored by the observed active latitudes; there is not a large poleward drift of active regions as they emerge. The time scale for emergence of an active region from the base of the convection zone to the surface is typically 2 - 4 months. The equatorial gap in the distribution of active regions has two possible origins; if the toroidal field strength is close to 10 5 G, it is due to the lack of equilibrium solutions at low latitude; if it is closer to 3 10 4 G, it may be due to modest poleward drift during emergence. (2) The tilt of active regions is due primarily to the Coriolis force acting to twist the diverging flows of the rising flux loops. The dispersion in tilts is caused primarily by the buffeting of flux tubes by convective motions as they rise through the interior. (3) The Coriolis force also bends the active region flux tube shape toward the following (i.e., anti-rotational) direction, resulting in a steeper leg on the following side as compared to the leading side of an active region. When the active region emerges through the photosphere, this results in a more rapid separation of the leading spots away from the magnetic neutral line as compared to the following spots. This bending motion also results in the neutral line being closer to the following magnetic polarity. (4) Active regions behave kinematically after they emerge because of 'dynamic disconnection', which occurs because of the lack of a solution to the hydrostatic equilibrium equation once the flux loop has emerged. This could explain why active regions decay once they have emerged, and why the advection-diffusion description of active regions works well after emergence. Smaller flux tubes may undergo 'flux tube explosion', a similar process, and provide a source for the constant emergence of small-scale magnetic fields. (5) The slight trend of most active regions to have a negative magnetic twist in the northern hemisphere and The National Center for Atmospheric Research is sponsored by the National Science Founda- tion.