A Multidisciplinary Study of Thermal Core-Mantle Coupling in Geodynamo Models

地球发电机模型中热核幔耦合的多学科研究

• 批准号: NE/H01571X/1
• 负责人: Christopher Davies
• 金额: $ 29.59万
• 依托单位: University of Leeds
• 依托单位国家: 英国
• 项目类别: Fellowship
• 财政年份: 2011
• 资助国家: 英国
• 起止时间: 2011 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FH01571X%2F1
• 关键词: Multidisciplinary; Study; Thermal; Core; Mantle

Earth's magnetic field is about as old as the Earth itself and its presence has broad implications for life on our planet. Used as a navigational aid by humans and animals for centuries, the magnetic field also shields Earth's surface from potentially harmful incoming radiation and protects the many man-made satellites orbiting the planet. Earth's magnetic field is generated in the outer core, a region of molten iron some 2800km below Earth's surface that is sandwiched between the solid inner core and mantle. Magnetic field lines, like strands of spaghetti, emerge from the outer core and thread through the solid mantle, finally appearing at Earth's surface and extending off into the atmosphere. When viewed at Earth's surface these field lines form a dipole, having north and south poles near the geographic poles. When viewed at the core-mantle boundary, the interface between the liquid core and the mantle, a much more complex picture emerges: the field contains four regions where magnetic field lines clump together, creating a patch. The patches are located under Canada, south America, Siberia and Australia. Earth's magnetic field also exhibits variations in time. Patches are stationary over the past 400 years, coinciding with the time-span over which the magnetic field has been directly measured, but appear to be more mobile over longer time periods. The most dramatic events are geomagnetic reversals, where the north and south magnetic poles flip. During reversals the shielding effect of the field is weakened and the impact on orbiting satellites could be severe; the effect of a reversal is unknown but life has survived the many reversals that have occurred to date. A complete understanding of how the Earth's magnetic field is generated and how reversals occur is of paramount importance for mitigating against the potential effects of such events. Crucial to this challenge is establishing why the present day field appears as it does, i.e. why is contains patches, whether patches are permanent features of the field, and whether there is a link between the present field and the field during and after a reversal. We model the physical processes in the outer core using computer simulations. Unfortunately, the task of simulating conditions in Earth's core is too great for current computers and so simplifications to the physical properties of the outer core are required in order to make progress. I have shown that simplified models produce realistic magnetic fields, including patches, when the flow of heat from the core to the mantle varies across the core-mantle boundary. This is the situation that occurs in the Earth: heat passes from the outer core to the mantle because the Earth is hottest in the middle, but more heat is lost beneath Africa and the Pacific than under Australia and the Gulf of Mexico. While predictions from these simple models are encouraging, the mechanism by which the patches are maintained is unlikely to apply when the physical properties of the real Earth are used in simulations. Moreover, the simulated fields do not contain the variability (such as reversals) seen in the observations. Earlier this year I observed a new process that can sustain patches through variations in core-mantle heat flow. The new process is theoretically applicable to the real Earth and is capable of producing the time-varying behaviour seen in observations. Additionally, I have recently presented the first detailed description of the computing power required to simulate physical properties approaching those of Earth's core. In this research proposal I will exploit these two discoveries to produce the first realistic models of the generation mechanism for Earth's magnetic field and elucidate the complex processes occurring in Earth's outer core in a manner never before possible.

地球磁场的历史与地球本身一样悠久，它的存在对我们星球上的生命有着广泛的影响。几个世纪以来，磁场一直被人类和动物用作导航工具，它还保护地球表面免受潜在有害的辐射，并保护许多绕地球轨道运行的人造卫星。地球的磁场产生于外核，这是一个位于地球表面以下约2800公里的熔融铁区域，夹在固体内核和地幔之间。磁力线就像意大利面条一样，从外核出现，穿过固体地幔，最终出现在地球表面，延伸到大气层。当在地球表面观察时，这些磁力线形成一个偶极子，在地理极点附近有北极和南极。当观察地核-地幔边界，即液体地核和地幔之间的界面时，一个更为复杂的画面出现了：磁场包含四个区域，磁场线聚集在一起，形成一个补丁。这些斑块位于加拿大、南美洲、西伯利亚和澳大利亚的下面。地球磁场也会随时间变化。在过去的400年里，斑块是静止的，与直接测量磁场的时间跨度相吻合，但在更长的时间内似乎更具移动的。最引人注目的事件是地磁反转，即北磁极和南磁极翻转。在逆转期间，磁场的屏蔽作用会减弱，对轨道卫星的影响可能会很严重;逆转的影响尚不清楚，但生命在迄今为止发生的多次逆转中幸存下来。完全了解地球磁场是如何产生的以及逆转是如何发生的，对于减轻此类事件的潜在影响至关重要。这一挑战的关键是确定为什么现在的场会出现这样的情况，即为什么它包含斑块，斑块是否是场的永久特征，以及在反转期间和之后，现在的场与场之间是否存在联系。我们用计算机模拟外核的物理过程。不幸的是，模拟地核条件的任务对于目前的计算机来说太大了，因此为了取得进展，需要简化外核的物理特性。我已经证明，当从地核到地幔的热流在地核-地幔边界发生变化时，简化的模型会产生真实的磁场，包括补丁。这就是地球上发生的情况：热量从外核传递到地幔，因为地球中部最热，但非洲和太平洋下面的热量损失比澳大利亚和墨西哥湾下面的热量要多。虽然这些简单模型的预测令人鼓舞，但当在模拟中使用真实的地球的物理特性时，维持斑块的机制不太可能适用。此外，模拟场不包含观测中看到的变化（如反转）。今年早些时候，我观察到一个新的过程，可以通过核幔热流的变化来维持斑块。新的过程理论上适用于真实的地球，并且能够产生观测中看到的随时间变化的行为。此外，我最近提出了第一个详细描述的计算能力所需的模拟物理性质接近地球的核心。在这个研究计划中，我将利用这两个发现来制作地球磁场产生机制的第一个现实模型，并以前所未有的方式阐明地球外核中发生的复杂过程。

项目成果

Inner core translation and the hemispheric balance of the geomagnetic field

内核平移与地磁场的半球平衡

• DOI: 10.1016/j.epsl.2015.05.028
• 发表时间: 2015
• 期刊: Earth and Planetary Science Letters
• 影响因子: 5.3
• 作者: Mound J

Geomagnetic field intensity and inclination records from Hawaii and the Réunion Island: Geomagnetic implications

夏威夷和留尼汪岛的地磁场强度和倾角记录：地磁影响

• DOI: 10.1016/j.pepi.2011.05.007
• 发表时间: 2011
• 期刊: Physics of the Earth and Planetary Interiors
• 影响因子: 2.3
• 作者: Laj C

The stratified layer at the core-mantle boundary caused by barodiffusion of oxygen, sulphur and silicon

• DOI: 10.1016/j.pepi.2012.11.001
• 发表时间: 2013-02-01
• 期刊: PHYSICS OF THE EARTH AND PLANETARY INTERIORS
• 影响因子: 2.3
• 作者: Gubbins, D.;Davies, C. J.
• 通讯作者: Davies, C. J.

Compositional instability of Earth's solid inner core

地球固体内核的成分不稳定性

• DOI: 10.1002/grl.50186
• 发表时间: 2013
• 期刊: Geophysical Research Letters
• 影响因子: 5.2
• 作者: Gubbins D

On the influence of a translating inner core in models of outer core convection

平移内核对外核对流模型的影响

• DOI: 10.1016/j.pepi.2012.10.001
• 发表时间: 2013
• 期刊: Physics of the Earth and Planetary Interiors
• 影响因子: 2.3
• 作者: Davies C