The origin of geomagnetic jerks
The origin of geomagnetic jerks
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DOI：
10.1038/nature01134
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发表时间：
2002-11-07
期刊：
影响因子：
64.8
通讯作者：
Dumberry, M
中科院分区：
文献类型：
--
作者：
Bloxham, J;Zatman, S;Dumberry, M
20世纪下半叶发生的地磁突变，1969年(参考文献1，2)，1978年(参考文献3，4)，1991年(参考文献3，4)。5)和1999年(参考文献6)是地球磁场的二次时间导数(长期加速度)的突变。冲击分离了几乎稳定的长期加速度周期，因此一阶时间导数(长期变化)表现为一系列由地磁冲击分隔的直线段。它们代表了长期变化的重组，这意味着它们来自内部(通过球谐分析(7)确定)，它们的短时间尺度意味着它们是由于地核表面流体流动的变化(也通过绘制地核表面随时间变化的流动图(8)确定的)。然而，人们对它们的物理起源知之甚少。在这里，我们表明，地磁急流可以用定常流动和简单的时变、轴对称、赤道对称的环状纬向流相结合来解释。这种流动与地球核心的扭转振荡是一致的，这是理论上预期的核心内的简单振荡流动(9)，并在核心流动模型(10)和数值发电机模型(11)中都观察到了这种流动。
Geomagnetic jerks, which in the second half of the twentieth century occurred in 1969 (refs 1, 2), 1978 (refs 3, 4), 1991 (ref. 5) and 1999 (ref. 6), are abrupt changes in the second time-derivative (secular acceleration) of the Earth's magnetic field. Jerks separate periods of almost steady secular acceleration, so that the first time-derivative (secular variation) appears as a series of straight-line segments separated by geomagnetic jerks. The fact that they represent a reorganization of the secular variation implies that they are of internal origin (as has been established through spherical harmonic analysis(7)), and their short timescale implies that they are due to a change in the fluid flow at the surface of the Earth's core (as has also been established through mapping the time-varying flow at the core surface(8)). However, little is understood of their physical origin. Here we show that geomagnetic jerks can be explained by the combination of a steady flow and a simple time-varying, axisymmetric, equatorially symmetric, toroidal zonal flow. Such a flow is consistent with torsional oscillations in the Earth's core, which are simple oscillatory flows in the core that are expected on theoretical grounds(9), and observed in both core flow models(10) and numerical dynamo models(11).