Beyond 1D Structure of Earth's Core - Reconciling Inferences from Seismic and Geomagnetic Observations

超越地核的一维结构 - 协调地震和地磁观测的推论

基本信息

  • 批准号:
    NE/W005247/1
  • 负责人:
  • 金额:
    $ 62.83万
  • 依托单位:
  • 依托单位国家:
    英国
  • 项目类别:
    Research Grant
  • 财政年份:
    2023
  • 资助国家:
    英国
  • 起止时间:
    2023 至 无数据
  • 项目状态:
    未结题

项目摘要

The geomagnetic field plays a key role in the Earth system by shielding the surface environment from a wind of charged particles emanating from the sun. However, this shielding effect is far from constant; the strength and structure of the field varies significantly in time. This can cause problems for international telecommunications and disrupt satellites as they pass through regions of weak field. To understand why the field changes we must look deep beneath our feet to Earth's iron core. It is in the core that our magnetic field is produced by an ocean of liquid iron alloy that is powered into turbulent motion by heat loss to the overlying mantle. Data from satellites and permanent observatories can be used to determine the magnetic field at the top of the core, but cannot directly provide information about the core's interior. Our understanding of Earth's magnetic field is therefore only as good as our knowledge of the core surface, and it is here that there have been significant new insights.Debate surrounding the dynamics at the top of Earth's core has persisted for over 40 years and has centred around one key question: is there a stable layer of fluid at the top of the core or is the whole core in turbulent motion? The distinction is critical because the existence of a stable layer would hide from observational view the key processes that generate the magnetic field in the core's turbulent interior. The two main tools for studying Earth's core are seismology and geomagnetism, unfortunately they provide conflicting evidence. Seismic studies find anomalously slow wave speeds in the uppermost core compared to what is expected for a turbulent region, implying there is a stable layer at the top of the core. Conversely, geomagnetic observations appear to require radial fluid motions at the top of the core, motions that would be absent in a stable layer.The crucial, and untested, assumption inherent in all previous work is that any stable stratification preventing turbulent convection in the core arises as a global layer. Using advanced computer simulations, we have recently discovered a new scenario is possible, that stratification occurs on a regional scale and not as a global layer. In our simulations, stable regions arise because the amount of heat leaving the core varies around the core-mantle boundary: radial motion in the core is suppressed by the unusually hot mantle under the central Pacific and Africa; conversely, radial core flow is enhanced where the cold mantle at American and east Asian longitudes draws more heat from the core. In this scenario, seismic and geomagnetic observations that apparently suggest different dynamics can be resolved within a single coherent framework. Our best estimates of temperature variations in the mantle suggest that both stable and unstable regions should exist in Earth's outermost core, the next step is to establish whether they do.A key aspect of this regional stratification scenario is that it can be tested using improvements in seismic and geomagnetic observations. We will test this model of regional structure and dynamics in the uppermost core by combining cutting-edge seismic processing techniques with state-of-the-art simulations of core dynamics and quantitative metrics for comparing simulated and observed magnetic fields. By enabling new seismic observations to drive new dynamical simulations and vice versa we will obtain a self-consistent picture of outer core dynamics and hence an improved understanding of how the core generates the magnetic field.
地磁场在地球系统中起着关键作用,它通过将表面环境免受从太阳散发出的带电颗粒的风掩盖。但是,这种屏蔽效果远非恒定。场的强度和结构随时间变化。这可能会导致国际电信的问题,并在卫星穿过薄弱领域的地区时破坏了卫星。要了解为什么田地发生变化,我们必须在脚下深处到地球的铁芯。在核心中,我们的磁场是由液态铁合金海洋产生的,该液体铁合金通过热量损失向上覆盖的地幔而驱动湍流。来自卫星和永久观测值的数据可用于确定核心顶部的磁场,但不能直接提供有关核心内部的信息。因此围绕一个关键问题:核心顶部的流体层是否稳定,还是整个核心在湍流运动中?区别至关重要,因为稳定层的存在将从观察视图中隐藏起来的关键过程,从而在核心的湍流内部产生磁场。研究地球核心的两个主要工具是地震学和地磁主义,不幸的是,它们提供了矛盾的证据。地震研究发现,与湍流区域的期望相比,最上层核心的慢速速度异常,这意味着核心顶部有一个稳定的层。相反,地磁观测似乎需要核心顶部的径向流体运动,在稳定层中不存在的运动。在所有以前的工作中,至关重要的,未经测试的假设是,任何稳定的分层都可以防止核心中的湍流对流在核心中。作为全球层出现。使用高级计算机模拟,我们最近发现了一种新方案,分层是在区域尺度上而不是全球层发生的。在我们的模拟中,稳定区域之所以出现,是因为留下核心的热量围绕核心壳边界有所不同:核心中的径向运动被中部太平洋和非洲下方异常热的地幔抑制。相反,在美国和东亚纵向的冷地幔从核心吸引更多热量的情况下,径向芯流得到了增强。在这种情况下,明显地表明不同动态的地震和地磁观察可以在单个连贯的框架内解决。我们对地幔中温度变化的最佳估计表明,稳定和不稳定区域都应该存在于地球最外部的核心中,下一步是确定它们是否做到。这种区域分层场景的关键方面是,可以使用改进来对其进行测试。地震和地磁观测。我们将通过将尖端的地震加工技术与核心动力学和定量指标的最新模拟结合使用,以比较模拟和观察到的磁场来测试最上层核心中区域结构和动力学模型。通过使新的地震观测能够驱动新的动力学模拟,反之亦然,我们将获得外核动力学的自一致图像,从而提高了对核心如何生成磁场的理解。

项目成果

期刊论文数量(1)
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Jonathan Mound其他文献

Jonathan Mound的其他文献

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{{ truncateString('Jonathan Mound', 18)}}的其他基金

Three-Dimensional Rotational Dynamics and Coupling of the Core-Mantle System
核幔系统三维旋转动力学与耦合
  • 批准号:
    NE/G002223/1
  • 财政年份:
    2010
  • 资助金额:
    $ 62.83万
  • 项目类别:
    Research Grant

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层状范德华晶体纳米线:调整 1D-2D 混合纳米结构结构和功能的机会
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