标题： 地球外核-地幔边界上的章动约束 显示英文标题

标题： Constraints on Earth's Core-Mantle boundary from nutation

摘要： 太阳和月亮引力的周期性变化会引起地球旋转轴方向的小变化，称为章动。 在地固参考系中测得的逆行准日频段的章动分量，会因与自由核章动（FCN）的共振而增强，FCN是地球流体外核的一种旋转模式。 地核-地幔边界（CMB）处的耗散过程会减弱这种共振，从而导致潮汐力与地球旋转响应之间的观测相位滞后。 这种相位滞后通常归因于地核与电导率较高的下地幔之间的电磁（EM）耦合。 然而，对CMB处地幔电导率和径向磁场强度的估计表明这些效应是不足的。 我们表明，缺失的耗散自然地来源于CMB处地形特征激发流体外核中的内波。 我们采用最初为海洋地形上的潮汐流开发的理论框架，计算了CMB地形引起的形状阻力和相关的功率通量。 我们的结果与CMB地形具有几公里均方根振幅的特征一致。 该模型倾向于支持外核顶部弱分层，尽管更强的分层也与更大的地形振幅相容。 这一机制提供了关于CMB地形和分层的独立约束，补充了地震学和磁观测。 其普遍性为探测类地行星深部动力学提供了一个新的框架。 显示英文摘要

摘要： Periodic variations in the Sun and Moon's gravitational pull cause small changes in Earth's rotational axis direction called nutation. Nutation components in the retrograde quasi-diurnal frequency band measured in the terrestrial reference frame are amplified by resonance with the Free Core Nutation (FCN), a rotational mode of Earth's fluid core. Dissipative processes at the core-mantle boundary (CMB) dampen this resonance, contributing to the observed phase lag between tidal forcing and Earth's rotational response. This phase lag is commonly attributed to electromagnetic (EM) coupling between the core and the electrically conducting lower mantle. However, estimates of mantle conductivity and radial magnetic field strength at the CMB suggest these effects are insufficient. We show that the missing dissipation arises naturally from the excitation of internal waves in the fluid core by topographic features at the CMB. Adapting a theoretical framework originally developed for tidal flow over oceanic topography, we compute the form drag and associated power flux induced by CMB topography. Our results are consistent with a CMB topography characterized by a root mean square amplitude of a few kilometers. The model favors weak stratification at the top of the core, though stronger stratification remains compatible with increased topographic amplitude. This mechanism provides independent constraints on CMB topography and stratification, complementing seismological and magnetic observations. Its generality offers a new framework for probing deep-interior dynamics across terrestrial planets.