S U M M A R Y The nature of the force balance that governs the geodynamo is debated. Recent theoretical analyses and numerical simulations support a quasigeotrophic (QG), magneto-ArchimedesCoriolis (MAC) balance in Earth’s core, where the Coriolis and pressure forces equilibrate at leading order in amplitude, and where the buoyancy, Lorentz and ageostrophic Coriolis forces equilibrate at the next order. In contrast, earlier theoretical expectations have favoured a magnetostrophic regime where the Lorentz force would reach leading order at the system scale. The dominant driver (buoyant or magnetic) for the general circulation in Earth’s core is equally debated. In this study, these questions are explored in the light of the high-quality geomagnetic data recently acquired by satellites and at magnetic ground observatories. The analysis involves inverse geodynamo modelling, a method that uses multivariate statistics extracted from a numerical geodynamo model to infer the state of Earth’s core from a geomagnetic field model interpretation of the main field and secular variation data. To test the QG-MAC dynamic hypothesis against the data, the framework is extended in order to explicitly prescribe this force balance into the inverse problem solved at the core surface. The resulting inverse solutions achieve a quantitatively adequate fit to the data while ensuring deviations from the QG-MAC balance (which amount to an inertial driving of the flow) lower than each of the leading forces. The general circulation imaged within the core over the past two decades confirms the existence of a planetary-scale, eccentric, axially columnar gyre that comprises an intense, equatorially symmetric jet at high latitudes in the Pacific hemisphere. The dominant driver of this circulation is shown to be of buoyant nature, through a thermal wind balance with a longitudinally hemispheric buoyancy anomaly distribution. Geomagnetic forecasts initiated with the inverted core states are systematically more accurate against the true interannual geomagnetic field evolution when enforcing the QG-MAC constraint. This force balance is therefore consistent with the geomagnetic data at the large scales of Earth’s core that can be imaged by the method.

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最近的地磁变化和地核的力平衡

总结 控制地球发电机的力平衡的性质是有争议的。最近的理论分析和数值模拟支持地核中的准地球营养 (QG)、磁阿基米德科里奥利 (MAC) 平衡，其中科里奥利力和压力在振幅的领先顺序上平衡，而浮力、洛伦兹和地转科里奥利力在下一个订单。相比之下，早期的理论预期有利于磁自转机制，其中洛伦兹力将在系统尺度上达到领先。地核一般环流的主要驱动力（浮力或磁力）同样存在争议。在这项研究中，这些问题是根据最近由卫星和磁地面观测站获得的高质量地磁数据进行的。该分析涉及逆地球动力学建模，该方法使用从数值地球动力学模型中提取的多元统计数据，从地磁场模型对主磁场和长期变化数据的解释推断地核的状态。为了根据数据测试 QG-MAC 动态假设，扩展框架以明确规定这种力平衡到在核心表面解决的逆问题。由此产生的逆解实现了对数据的定量足够拟合，同时确保与 QG-MAC 平衡（相当于流动的惯性驱动）的偏差低于每个主力。过去二十年在地核内成像的一般环流证实了行星尺度的、偏心的、轴向柱状环流的存在，其中包括强烈的、太平洋半球高纬度的赤道对称急流。通过具有纵向半球浮力异常分布的热风平衡，表明这种环流的主要驱动力具有浮力性质。当强制执行 QG-MAC 约束时，以倒置的核心状态启动的地磁预测相对于真实的年际地磁场演化系统更准确。因此，这种力平衡与可以通过该方法成像的大尺度地核的地磁数据一致。当强制执行 QG-MAC 约束时，以倒置的核心状态启动的地磁预测相对于真实的年际地磁场演化系统更准确。因此，这种力平衡与可以通过该方法成像的大尺度地核的地磁数据一致。当强制执行 QG-MAC 约束时，以倒置的核心状态启动的地磁预测相对于真实的年际地磁场演化系统更准确。因此，这种力平衡与可以通过该方法成像的大尺度地核的地磁数据一致。