Effects of Topographic Boundary Heterogeneity on Earth's Core Dynamics

长期以来，研究人员一直认为，地球的核心过程发生在近乎完美的球壳中，这一条件足以解释大多数大地测量和地磁观测。然而，地震调查和地幔对流模拟表明，核-地幔边界包含形状和温度的变化，形成了一种不均匀的边界。最近的模型表明，边界不均匀可能既控制了地球磁场的大规模产生(例如Christensen和Olson，2003)，也控制了地幔和地核之间的角动量交换(例如Hide，1969；Jault，2003)。事实上，非均质边界的影响可能是影响地球核心过程的最重要的控制因素之一。然而，很少有实验室实验来研究热非均质性的影响(Sumita and Olson，1999；2002)，还没有人研究地形非均质性的影响。在这项研究中，研究者将采用实验室和数值实验相结合的方法来测量非均质边界地形对岩心流动的影响。结果将允许测试岩心流动是否会被地形凸起锁定在适当的位置。他们还将利用我们的结果来估计核-地幔边界的粘性力矩和压力矩，这些力矩会影响地球的自转和日长的变化(Jault和Lemouel，1989,1999；Kuang和Bloxham，1993；Kuang和Chao，2001)。

Researchers have long assumed that Earth's core processes occur withina nearly perfect spherical shell and that this condition is sufficientto explain most of the geodetic and geomagnetic observations. However,seismic investigations and mantle convection simulations suggest thatthe core-mantle boundary contains variations in shape and temperature,creating a heterogeneous boundary. Recent models suggest that boundaryheterogeneities may control both the large-scale generation of theEarth's magnetic field (e.g., Christensen and Olson, 2003) and theexchange of angular momentum between the mantle and core (e.g., Hide,1969; Jault, 2003). In fact, the effects of heterogeneous boundariesmay be one of the most important controlling factors influencingEarth's core processes. However, there are few laboratory experimentsthat have been conducted to study the effects of thermal heterogeneity(Sumita and Olson, 1999; 2002) and none to study the effects oftopographic heterogeneity.In this study, the investigators will measure the effects of heterogeneousboundary topography on core flows, using coupled laboratory and numericalexperiments. The results will allow a test of whether core flow canbecome locked in place by topographic bumps. They will also use ourresults to estimate the viscous and pressure torques at the core-mantleboundary, which affect the rotation of the Earth and variations in thelength of day (Jault and Lemouel, 1989, 1999; Kuang and Bloxham, 1993;Kuang and Chao, 2001).