近日，加拿大阿尔伯塔大学Dumberry, Mathieu团队揭示了引力转矩驱动日长的数十年尺度变化。2026年9月23日出版的《自然》杂志发表了这项成果。

在十年尺度上，日长（LOD）的波动主要由地幔与地核之间的角动量交换引起。为解释这种交换，学界已提出若干机制，包括核幔边界（CMB）处的电磁耦合和地形耦合，以及内核施加的引力转矩。然而，核幔转矩的精确性质仍不清楚。

研究组表明，地震学重建的内核差异旋转和由磁场变化推导的核流表明，数十年尺度的日长变化主要由引力转矩驱动，并受到电磁转矩和地形转矩的阻碍，这与类地发电机模型的结果一致。研究组重建的转矩历史虽然取决于内核旋转和核流模型的准确性，但支持最下部地幔具有以下特征：近中性浮力的热化学堆、低黏度的后钙钛矿（pPv）相，以及其底部厚几公里的高导电富铁层。该结果还表明，低黏度内核仅在几年内发生变形，并给出了流体地核顶部层结程度的上限。总之，该研究有助于使地球最深处正在浮现的图景变得清晰。

附：英文原文

Title: Gravitational torque drives multidecadal variations in length of day

Author: Zhang, Huifeng, Dumberry, Mathieu

Issue&Volume: 2026-09-23

Abstract: Fluctuations in the length of day (LOD) on decadal timescales are caused primarily by an exchange of angular momentum between the Earth’s mantle and core1,2,3. Several mechanisms have been proposed to explain this exchange, including electromagnetic4,5,6,7 and topographic8,9,10 coupling at the core–mantle boundary (CMB) and a gravitational torque by the inner core11,12. However, the precise nature of the core–mantle torque remains unknown. Here we show that the seismically reconstructed differential rotation of the inner core13,14,15 and core flows derived from magnetic field changes16,17 suggest that the multidecadal LOD changes are driven primarily by the gravitational torque and resisted by electromagnetic and topographic torques, consistent with results from Earth-like dynamo models18. Our reconstructed torque histories, although tied to the accuracy of the inner core rotation and core flow models, support a lowermost mantle that features near-neutrally buoyant thermochemical piles19,20,21, a post-perovskite (pPv) phase with a low viscosity22 and a highly conducting23,24 iron-enriched layer a few kilometres thick at its base25. Our results also suggest a low-viscosity inner core deforming in only a few years26,27,28 and yield an upper limit on the stratification at the top of the fluid core. Altogether, our study contributes to bringing into focus an emerging picture of the deepest regions of our planet.

DOI: 10.1038/s41586-026-10999-2

Source: https://www.nature.com/articles/s41586-026-10999-2