Fluctuations in the rotation rate of the solid Earth over periods from 5 to 100 years result from exchanges of angular momentum between the fluid outer core and the solid mantle. The coupling mechanism mediating angular momentum transfer is not clear yet. Here, I revisit local Cartesian models for the pressure stress on a bumpy core-mantle interface. One common approach consists in analyzing forced magnetohydrodynamic modes arising from the interaction between a steady flow along the core-mantle interface and boundary topography. The wave amplitude scales as the height ζ of corrugations and the pressure stress as ζ 2. As expected from Newton's third law, the tangential stress on the fluid is opposite to the tangential stress on the solid. It is exactly compensated by non zero mean electromagnetic and Coriolis forces, which both result from interactions at infinity and not with the electrically insulating solid. Requiring zero net flux of mass and electrical current at infinity in order to better model closed systems necessitates to restore mean flow acceleration. This makes possible to investigate whether there is momentum transfer into the fluid interior or instead dissipation next to the boundary. Fluid stratification enhances the horizontal stress exerted by the pressure field on the core-mantle boundary but we have yet to describe the mechanism to transport momentum from the boundary into the fluid.

中文翻译：

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核-地幔界面的切向应力

固体地球自转率在 5 到 100 年间的波动是由于流体外核和固体地幔之间角动量的交换造成的。介导角动量传递的耦合机制尚不清楚。在这里，我重新审视了颠簸的核-地幔界面上的压力应力的局部笛卡尔模型。一种常见的方法是分析由沿核-地幔界面的稳定流和边界地形之间的相互作用引起的强迫磁流体动力学模式。波幅与波纹的高度 ζ 成比例，压力应力为 ζ 2。正如牛顿第三定律所预期的那样，流体上的切向应力与固体上的切向应力相反。它由非零平均电磁力和科里奥利力精确补偿，这两者都是由无穷远的相互作用引起的，而不是与电绝缘固体的相互作用。为了更好地模拟封闭系统，需要在无穷远处质量和电流的净通量为零，因此需要恢复平均流动加速度。这使得研究是否有动量转移到流体内部或在边界附近消散成为可能。流体分层增强了压力场对地核-地幔边界施加的水平应力，但我们还没有描述将动量从边界传输到流体的机制。这使得研究是否有动量转移到流体内部或在边界附近耗散成为可能。流体分层增强了压力场对地核-地幔边界施加的水平应力，但我们还没有描述将动量从边界传输到流体的机制。这使得研究是否有动量转移到流体内部或在边界附近耗散成为可能。流体分层增强了压力场对地核-地幔边界施加的水平应力，但我们还没有描述将动量从边界传输到流体的机制。