Reversal of drift direction during the Laschamp geomagnetic excursion

IF 2.4 3区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS Physics of the Earth and Planetary Interiors Pub Date : 2024-02-01 DOI:10.1016/j.pepi.2024.107143
Nicole Clizzie, Catherine Constable
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Abstract

Earth's magnetic field changes in both space and time: the temporal changes are called geomagnetic and paleomagnetic secular variations. Westward drift has been noted as a feature of secular variation for several centuries, but eastward drift has received less attention. We use three global geomagnetic field models covering the past 100 kyr to extend temporal coverage for tracking the zonal (azimuthal) motion of the radial magnetic field. The models we use are GGF100k (100–0 ka), GGFSS70 (70–15 ka), LSMOD.2 (50–30 ka); the extent of the models enables the inclusion of the extreme secular variations found during excursions, particularly the Laschamp excursion (42–40 ka). GGFSS70 and LSMOD.2 have higher temporal resolution than GGF100k, but their underlying data have poorer spatial coverage. Spatial structure is greatly diminished in all models for spherical harmonic degrees l>4.

We use two types of time-longitude plots, one of the full radial field to expose reverse and intense flux patches at the core-mantle boundary. The second time-longitude plot is processed to enhance zonal motion signatures and allows us to use Radon drift analyses to uncover characteristic time scales of both westward and eastward drift at mid to high latitudes in both the northern and southern hemispheres. Our results differ across the three models, which we attribute to varying degrees of resolution, accuracy, and data distribution. Nevertheless, recurrent episodes of both eastward and westward drift ranging from ±0.05o/yr to ±0.18o/yr occur in both the northern and southern hemispheres. Westward drift dominates. We also observe 8–20 kyr intervals between occurrences of high-latitude reverse flux patches correlated with strong drift signals. Focusing on the period 50–30 ka, we observe dominant eastward drift preceding the Laschamp excursion and westward drift subsequently. In a period not associated with an excursion, 90–80 ka, we see strong mid to high latitude drift signatures in the northern hemisphere.

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拉尚地磁偏移期间漂移方向的逆转
地球磁场在空间和时间上都会发生变化:时间上的变化被称为地磁和古地磁世变。西向漂移作为时变的一个特征已被注意了几个世纪,但东向漂移却较少受到关注。我们使用了三个覆盖过去 100 kyr 的全球地磁场模型,以扩大时间覆盖范围,跟踪径向磁场的带状(方位角)运动。我们使用的模型是:GGF100k(100-0 ka)、GGFSS70(70-15 ka)、LSMOD.2(50-30 ka);这些模型的范围使得在偏移,特别是拉尚偏移(42-40 ka)期间发现的极端时序变化也包括在内。GGFSS70 和 LSMOD.2 的时间分辨率高于 GGF100k,但其基础数据的空间覆盖范围较小。我们使用了两种时间-纬度图,一种是全径向场图,以揭示地核-地幔边界的反向强通量斑块。第二种时间纬度图经过处理,增强了地带运动特征,使我们能够利用拉顿漂移分析,揭示南北半球中高纬度地区西向和东向漂移的特征时间尺度。三个模式的结果各不相同,我们将其归因于不同程度的分辨率、精度和数据分布。尽管如此,南北半球还是反复出现了±0.05o/年到±0.18o/年的东漂和西漂现象。西向漂移占主导地位。我们还观察到高纬度反向通量斑块的出现与强烈漂移信号相关的8-20 kyr间隔。在 50-30 ka 期间,我们观察到在拉斯汉普偏移之前主要是向东漂移,之后则是向西漂移。在与偏移无关的 90-80 ka 期间,我们在北半球看到了强烈的中高纬度漂移信号。
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来源期刊
Physics of the Earth and Planetary Interiors
Physics of the Earth and Planetary Interiors 地学天文-地球化学与地球物理
CiteScore
5.00
自引率
4.30%
发文量
78
审稿时长
18.5 weeks
期刊介绍: Launched in 1968 to fill the need for an international journal in the field of planetary physics, geodesy and geophysics, Physics of the Earth and Planetary Interiors has now grown to become important reading matter for all geophysicists. It is the only journal to be entirely devoted to the physical and chemical processes of planetary interiors. Original research papers, review articles, short communications and book reviews are all published on a regular basis; and from time to time special issues of the journal are devoted to the publication of the proceedings of symposia and congresses which the editors feel will be of particular interest to the reader.
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