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The dynamic evolution of active-region-scale magnetic flux tubes in the turbulent solar convective envelope.

机译:湍流太阳对流包层中有源区尺度磁通管的动态演化。

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摘要

The Sun exhibits cyclic properties of its large-scale magnetic field on the order of sigma22 years, with a ∼11 year frequency of sunspot occurrence. These sunspots, or active regions, are the centers of magnetically driven phenomena such as flares and coronal mass ejections. Volatile solar magnetic events directed toward the Earth pose a threat to human activities and our increasingly technological society. As such, the origin and nature of solar magnetic flux emergence is a topic of global concern.;Sunspots are observable manifestations of solar magnetic fields, thus providing a photospheric link to the deep-seated dynamo mechanism. However, the manner by which bundles of magnetic field, or flux tubes, traverse the convection zone to eventual emergence at the solar surface is not well understood. To provide a connection between dynamo-generated magnetic fields and sunspots, I have performed simulations of magnetic flux emergence through the bulk of a turbulent, solar convective envelope by employing a thin flux tube model subject to interaction with flows taken from a hydrodynamic convection simulation computed through the Anelastic Spherical Harmonic (ASH) code. The convective velocity field interacts with the flux tube through the drag force it experiences as it traverses through the convecting medium.;Through performing these simulations, much insight has been gained about the influence of turbulent solar-like convection on the flux emergence process and resulting active region properties. I find that the dynamic evolution of flux tubes change from convection dominated to magnetic buoyancy dominated as the initial field strength of the flux tubes increases from 15 kG to 100 kG. Additionally, active-region-scale flux tubes of 40 kG and greater exhibit properties similar to those of active regions on the Sun, such as: tilt angles, rotation rates, and morphological asymmetries. The joint effect of the Coriolis force and helical motions present in convective upflows help tilt the apex of rising flux tubes toward the equator in accordance with Joys Law.;Utilizing these simulations, I find that rotationally aligned, columnar convective structures called giant cells present near the equatorial regions of the ASH simulation organizes flux emergence into a large-scale longitudinal pattern similar to the active longitude trend on the Sun and other solar-like stars. The effect of radiative diffusion across the radiation zone-convection zone interface on the buoyant rise of magnetic flux tubes is also studied. Incorporating this effect into the flux tube model, flux tubes with magnetic field strengths of 60 kG or less no longer anchor in the stably stratified overshoot region. These flux tubes still have average emergence properties that agree with observations of solar active regions, although tilt angles have a larger scatter about the mean value. Finally, I will discuss possible future research problems that can be investigated through the thin flux tube approach, such as convection-induced twisting of the flux tube magnetic field lines and flux emergence properties on a young Sun rotating at 5 times the current solar rate.
机译:太阳表现出其大范围磁场的循环特性,约为sigma22年,太阳黑子的发生频率约为11年。这些黑子或活动区域是磁驱动现象的中心,例如耀斑和日冕物质抛射。指向地球的挥发性太阳磁事件对人类活动和我们日趋发展的技术社会构成威胁。因此,太阳磁通出现的起源和性质是一个全球关注的话题。黑子是太阳磁场的可观察到的表现,因此为深层发电机机制提供了光球联系。但是,人们对磁场束或通量管横穿对流区并最终出现在太阳表面的方式的了解还很少。为了提供发电机产生的磁场和太阳黑子之间的联系,我通过使用薄的通量管模型进行了与湍流,太阳对流包层的整体中磁通量出现的模拟,该模型受与水动力对流模拟计算得出的流的相互作用通过非弹性球谐(ASH)代码。对流速度场通过流过对流介质时受到的阻力与通量管相互作用。通过进行这些模拟,已经获得了关于湍流太阳对流对通量出现过程和结果的影响的许多见解。活动区域属性。我发现,随着通量管的初始场强从15 kG增加到100 kG,通量管的动态演变从对流主导变为磁浮力主导。此外,大于或等于40 kG的活动区域规模的通量管具有类似于太阳活动区域的特性,例如:倾斜角,旋转速率和形态不对称性。对流上升流中存在的科里奥利力和螺旋运动的共同作用有助于根据乔伊斯定律使上升的通量管的顶点向赤道倾斜。利用这些模拟,我发现旋转对准的圆柱状对流结构称为巨胞ASH模拟的赤道区域将通量出现组织为大规模的纵向模式,类似于太阳和其他类似太阳的恒星的活跃经度趋势。还研究了穿过辐射区-对流区界面的辐射扩散对磁通管浮力上升的影响。将这种效应纳入通量管模型后,磁场强度为60 kG或更小的通量管不再锚定在稳定的分层过冲区域中。这些通量管的平均出射特性仍然与太阳活动区域的观察结果一致,尽管倾斜角在平均值附近具有较大的散射。最后,我将讨论可以通过细通量管方法研究的未来可能存在的研究问题,例如对流引起的通量管磁场线的扭曲以及在以当前太阳速度的5倍旋转的年轻太阳上的通量出射特性。

著录项

  • 作者

    Weber, Maria Ann.;

  • 作者单位

    Colorado State University.;

  • 授予单位 Colorado State University.;
  • 学科 Physics Astronomy and Astrophysics.
  • 学位 Ph.D.
  • 年度 2014
  • 页码 304 p.
  • 总页数 304
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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