Forward models of torsional waves: dispersion and geometric effects
Forward models of torsional waves: dispersion and geometric effects
复制标题
扭转波的正演模型：色散和几何效应
DOI：
10.1093/gji/ggt414
复制
发表时间：
2014
影响因子：
2.8
通讯作者：
Cox G
中科院分区：
文献类型：
--
作者：
Cox G
Alfvén波是在周围磁场存在的情况下在导电流体中传播的一组横波。对地球内部这种波的研究很重要，因为它们可以用来推断地核的结构和物理性质，否则这些结构和物理性质仍然是无法获得的。我们建立了地核中柱面扭转Alfvén波的一维正演模型，也称为扭转振荡，并研究了它们在满球和赤道对称球壳中的演化。在这里，我们发现行进扭转波经历了显著的几何色散，这种色散随着来自边界的连续反射而增加，使得初始波脉冲在核心的三次穿越内变得不可识别。在传播过程中，低幅度尾迹尾随清晰定义的脉冲，我们用惠更斯原理在偶数维上的失效来解释这一现象。我们研究了几何色散与波长的关系，得出长波长特征比短波长特征更具色散性的结论。这一结果特别重要，因为从长期变化中推断出的地核中的扭转波是相对较长的波长，因此很可能在地核内经历显著的弥散。当对角速度采用无应力边界条件时，波在核幔边界赤道处反射，反射符号与入射波相同。通过旋转轴的波经历伪反射，并且由于相移而表现出更复杂的行为。在赤道对称的壳体中，由于几何效应，我们发现在切线柱面上有弱反射。
Alfvén waves are a set of transverse waves that propagate in an electrically conducting fluid in the presence of an ambient magnetic field. Studies of such waves in the Earth's interior are important because they can be used to make inferences about the structure and physical properties of the core that would otherwise remain inaccessible. We produce 1-D forward models of cylindrical torsional Alfvén waves in the Earth's core, also known as torsional oscillations, and study their evolution in a full sphere and an equatorially symmetric spherical shell. Here, we find that travelling torsional waves undergo significant geometric dispersion that increases with successive reflections from the boundaries such that an initial wave pulse becomes unidentifiable within three transits of the core. Low amplitude wakes trail behind sharply defined pulses during propagation, a phenomenon that we interpret using the failure of Huygens’ principle in even dimensions. We investigate the relationship between geometric dispersion and wavelength, concluding that long-wavelength features are more dispersive than short-wavelength features. This result is particularly important because torsional waves that have been inferred in the Earth's core from secular variation are relatively long wavelength, and are therefore likely to undergo significant dispersion within the core. When stress-free boundary conditions on angular velocity are applied, waves are reflected at the equator of the core–mantle boundary with the same sign as the incident wave. Waves that pass through the rotation axis undergo a pseudo-reflection and display a more complicated behaviour due to a phase shift. In an equatorially symmetric shell, we identify a weak reflection at the tangent cylinder due to geometric effects.
登录
查看更多内容
地核电磁驱动向西漂移和内核超级旋转
DOI：
--
发表时间：
2013
影响因子：
11.1
作者：
P. Livermore;Rainer Hollerbach;A. Jackson
通讯作者：
A. Jackson
圆形膜波的焦点相移，应用于欠膨胀超音速喷气结构
DOI：
--
发表时间：
1995
期刊：
影响因子：
--
作者：
A. Powell
通讯作者：
A. Powell
发电机模拟中的扭转振荡
影响因子：
2.8
作者：
Johannes Wicht;U. Christensen
通讯作者：
U. Christensen
影响因子：
2.8
作者：
S. Zatman;J. Bloxham
通讯作者：
S. Zatman;J. Bloxham
地球发电机数值模型中的扭矩平衡、泰勒约束和扭转振荡
DOI：
--
发表时间：
2003
期刊：
影响因子：
--
作者：
M. Dumberry;J. Bloxham
通讯作者：
J. Bloxham