Searching for geomagnetic spikes in numerical dynamo simulations
Searching for geomagnetic spikes in numerical dynamo simulations
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DOI：
10.1016/j.epsl.2018.09.037
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发表时间：
2018-12-15
影响因子：
5.3
通讯作者：
Constable, Catherine G.
中科院分区：
文献类型：
--
作者：
Davies, Christopher J.;Constable, Catherine G.
我们使用数值发电机模拟研究地磁场强度的快速变化。这项工作的动机是古地磁观测的“地磁尖峰”，事件的场强上升，然后下降了2-3倍，在十年的时间尺度和一个有限的空间区域。历史记录中尚未发现类似事件，因此地磁尖峰可能包含有关地球发电机运行的新的重要信息。然而，它们也是有争议的，因为现有数据的不确定性和分辨率限制阻碍了确定其时空特征的努力。这引发了关于这种极端事件是否起源于地球液体核心的争论。地球发电机模拟产生高时空分辨率的强度信息，但必须小心解释，因为它们还不能在地球的液体核心的条件下运行。我们采用反向和非反向地球发电机模拟运行在不同的物理条件下，并考虑各种方法的缩放结果，以允许与地球进行比较。在每个模拟中，我们搜索“极端事件”，定义为连续时间点之间的最大强度差，在地球表面的2度经纬度网格上的每个位置，从而不对事件的时空特征进行假设。极端事件在一些模拟中显示尖峰形的时间序列，尽管它们通常关于峰值强度是不对称的。在几个模拟中，最大变化率达到0.75 mu Tyr（-1），这是峰值估计值的下限，表明此类事件可能源自核心。最快的变化通常发生在大于50度的纬度，这可以用来指导未来的数据采集。模拟中的极端事件是由于通量斑块在内核表面迁移时迅速增强而产生的，而不是来自内核内部的通量。在古地磁记录中观察到更多尖峰的前景似乎取决于在正确的位置和时间找到样本来采样通量斑块演化的这个特定阶段。(C)2018由Elsevier B. V.出版
We use numerical dynamo simulations to investigate rapid changes in geomagnetic field intensity. The work is motivated by paleomagnetic observations of 'geomagnetic spikes', events where the field intensity rose and then fell by a factor of 2-3 over decadal timescales and a confined spatial region. No comparable events have been found in the historical record and so geomagnetic spikes may contain new and important information regarding the operation of the geodynamo. However, they are also controversial because uncertainties and resolution limitations in the available data hinder efforts to define their spatiotemporal characteristics. This has led to debate over whether such extreme events can originate in Earth's liquid core. Geodynamo simulations produce high spatio-temporal resolution intensity information, but must be interpreted with care since they cannot yet run at the conditions of Earth's liquid core. We employ reversing and non-reversing geodynamo simulations run at different physical conditions and consider various methods of scaling the results to allow comparison with Earth. In each simulation we search for 'extremal events', defined as the maximum intensity difference between consecutive time points, at each location on a 2 degrees latitude-longitude grid at Earth's surface, thereby making no assumptions regarding the spatio-temporal character of the event. Extremal events display spike-shaped time-series in some simulations, though they can often be asymmetric about the peak intensity. Maximum rates of change reach 0.75 mu Tyr(-1) in several simulations, the lower end of estimates for spikes, suggesting that such events can originate from the core. The fastest changes generally occur at latitudes > 50 degrees, which could be used to guide future data acquisitions. Extremal events in the simulations arise from rapid intensification of flux patches as they migrate across the core surface, rather than emergence of flux from within the core. The prospect of observing more spikes in the paleomagnetic record appears contingent on finding samples at the right location and time to sample this particular phase of flux patch evolution. (C) 2018 Published by Elsevier B.V.