Department of Earth and Planetary Science, University of California, Berkeley, California 94720, USA.
Nature. 2010 Dec 16;468(7326):952-4. doi: 10.1038/nature09643.
Magnetic fields at the Earth's surface represent only a fraction of the field inside the core. The strength and structure of the internal field are poorly known, yet the details are important for our understanding of the geodynamo. Here I obtain an indirect estimate for the field strength from measurements of tidal dissipation. Tidally driven flow in the Earth's liquid core develops internal shear layers, which distort the internal magnetic field and generate electric currents. Ohmic losses damp the tidal motions and produce detectable signatures in the Earth's nutations. Previously reported evidence of anomalous dissipation in nutations can be explained with a core-averaged field of 2.5 mT, eliminating the need for high fluid viscosity or a stronger magnetic field at the inner-core boundary. Estimates for the internal field constrain the power required for the geodynamo.
地球表面的磁场仅代表地核内部磁场的一小部分。内部磁场的强度和结构知之甚少，但这些细节对于我们理解地球发电机至关重要。在这里，我通过潮汐耗散的测量获得了磁场强度的间接估计。地球液态核心中潮汐驱动的流动会产生内部剪切层，这些剪切层会扭曲内部磁场并产生电流。欧姆损耗会阻尼潮汐运动，并在地球章动中产生可检测的特征。先前在章动中报告的异常耗散的证据可以用平均场强为 2.5 mT 的核心来解释，从而消除了对高流体粘度或内核边界更强磁场的需求。对内部磁场的估计限制了地发电机所需的功率。
