Earth's core internal dynamics 1840-2010 imaged by inverse geodynamo modelling
Earth's core internal dynamics 1840-2010 imaged by inverse geodynamo modelling
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DOI：
10.1093/gji/ggu064
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发表时间：
2014-06-01
影响因子：
2.8
通讯作者：
Aubert, Julien
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文献类型：
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作者：
Aubert, Julien
逆地球发电机模型试图从地磁数据和地球发电机的自洽三维数值模型所带来的统计信息来估计地核的动态。该方法依赖于约束条件下使用最小二乘反演，并利用线性关系和长期的统计相关性与磁观测估计隐藏量。这些数据及其误差统计由地磁场模型COV-OBS、gufm-sat-Q3和CM 4提供，涵盖1840-2010年。先前的数值模型是最近出版的耦合地球发电机，其输出呈现出高度的形态学的语义的地磁场，同时再现其长期变化的主要特征。对数据的反演失配的分析表明，在整个调查时间段内，先验模型通常在其指定误差范围内很好地解释了主要场和长期变化数据。倒转的核心流被证实主要是组织在平行于地球自转轴的列。先前观测到的一个巨大的偏心柱状环流的西向漂移流被发现存在于1870年以后，它的结构被证明是缓慢地向西旋转的速度高达0.1A度A年（-1），证实了早期的预测直接数值模拟的基础上。时间的变化，在轴对称部分的环流准确地占观察到的变化，在最近的时代的一天的长度。倒置的磁结构支持的对流柱的方位角通量驱逐的机制来解释低纬度磁通补丁存在于大西洋下面的起源。1840-2010年的时间平均反演密度异常场具有纵向半球结构，大部分浮力在东半球，与该半球成像的对流柱的快速激增一致，与早期提出的更快的内核冻结在那里，以及固体内核可能的东西对流平移。在反演中观察到的流量变化的典型时间尺度比直接模拟先前模型自然产生的时间尺度短两到三倍，这突出了其在充分呈现地球核心短时间尺度动态方面的局限性。
Inverse geodynamo modelling seeks to estimate the dynamic state of Earth's core from geomagnetic data and the statistical information brought by a prior self-consistent, 3-D numerical model of the geodynamo. The method rests on the use of least-squares inversions under constraints and estimates hidden quantities by taking advantage of linear relations and long-range statistical correlations with the magnetic observations. The data, together with their error statistics, are provided by geomagnetic field models COV-OBS, gufm-sat-Q3 and CM4, covering epochs 1840-2010. The prior numerical model is the recently published coupled Earth dynamo, the output of which presents a high degree of morphological semblance to the geomagnetic field while reproducing the main features of its secular variation. An analysis of the inversion misfits to the data shows that the prior model generally accounts well for the main field and secular variation data within their specified errors, throughout the investigated time period. Inverted core flows are confirmed to be mainly organized in columns parallel to the Earth's rotation axis. A previously observed giant eccentric columnar gyre of westward-drifting flow is found to be present from epoch 1870 onwards, and its structure is shown to slowly rotate westwards at a rate up to 0.1A degrees A yr(-1), confirming an earlier prediction based on direct numerical modelling. Temporal variations in the axisymmetric part of the gyre accurately account for observed variations of the length of the day in recent epochs. Inverted magnetic structures support a mechanism of azimuthal flux expulsion by convective columns to explain the origin of low-latitude magnetic flux patches existing beneath the Atlantic. The 1840-2010 time average of the inverted density anomaly field has a longitudinal hemispheric structure, with most of the buoyancy in the Eastern hemisphere, consistent with rapid surges of convective columns imaged in this hemisphere, with earlier proposals of a faster inner core freezing there, and with a possible east-to-west convective translation of the solid inner core. The typical timescales of flow variation observed in the inversions are two to three times shorter than those naturally produced by a direct simulation of the prior model, underlining its limits in fully rendering the Earth's core short timescale dynamics.