On the Mantle-Inner Core Gravitational Oscillation Under the Action of the Electromagnetic Coupling Effects
On the Mantle-Inner Core Gravitational Oscillation Under the Action of the Electromagnetic Coupling Effects
复制标题
电磁耦合效应作用下的地幔-内核引力振荡
DOI：
10.1029/2019jb018863
复制
发表时间：
2020-02-01
影响因子：
3.9
通讯作者：
Huang, Chengli
中科院分区：
文献类型：
--
作者：
Duan, Pengshuo;Huang, Chengli
先前的工作表明，地幔-内核引力耦合模式的本征周期可以与观测到的6年周期的日长相匹配。然而，这种模式只是一个理想模型，因为它不涉及电磁（EM）耦合效应。在此，我们进一步研究了电磁耦合效应作用下的地幔-内核引力模式及其数学方程，同时给出了相关的阻尼振荡解析解。根据该理论模型，我们可以约束核幔引力耦合强度Gamma（>6.5 x 10(19) Nm），并推断出核幔边界（CMB）和内核边界处的电磁耦合信息。这项工作表明，部分液芯必须与内核（IC）耦合，并作为一个整体与 IC 一起轴向旋转，这支持了最近的假设，即所谓的切线圆柱体内只有部分液芯被锁定到 IC。这种解释可以大大削弱内核边界剪切振荡引起的扰动磁场，并消除相关的电磁阻尼耗散，否则，预测的6年振荡将迅速衰减，弛豫时间类似于9.8天。此外，我们还给出了6年振荡的理论品质因数Q值的物理表达式，该值主要与CMB处的电磁耦合有关。根据CMB典型的电磁耦合参数，预测理论Q值在40-75范围内，与当前观测结果一致（与51.6类似）。
Previous works indicated that the eigenperiod of the mantle-inner core gravitational coupling mode can match the observed 6-year period in length-of-day. However, this mode is only an ideal model, since it does not involve the electromagnetic (EM) coupling effects. Here, we further study the mantle-inner core gravitational mode and its mathematical equation under the action of the EM coupling effects, while the relevant damping oscillation analytical solution is also given. According to this theoretical model, we can constrain the core-mantle gravitational coupling strength Gamma (>6.5 x 10(19) Nm) and infer the EM coupling information at the core-mantle boundary (CMB) and the inner core boundary. This work indicates that a partial liquid core is necessarily required to be coupled to the inner core (IC) and axially rotates with the IC as a single body, which supports the recent assumption that only a part fluid core within the so-called tangent cylinder is locked to the IC. This explanation can greatly weaken the perturbation magnetic field due to the shear oscillation at the inner core boundary and eliminate the relevant EM damping dissipation, otherwise, the predicted 6-year oscillation will be rapidly decayed with a relaxation time similar to 9.8 days. In addition, we give the physical expression of the theoretical quality factor Q value of the 6-year oscillation, which is mainly related to the EM coupling at the CMB. According to the typical EM coupling parameters at the CMB, the theoretical Q value is predicted in the range of 40-75, which coincides with the current observed result (similar to 51.6).