A 3-DIMENSIONAL CONVECTIVE DYNAMO SOLUTION WITH ROTATING AND FINITELY CONDUCTING INNER-CORE AND MANTLE
A 3-DIMENSIONAL CONVECTIVE DYNAMO SOLUTION WITH ROTATING AND FINITELY CONDUCTING INNER-CORE AND MANTLE
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DOI：
10.1016/0031-9201(95)03049-3
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发表时间：
1995-09-01
影响因子：
2.3
通讯作者：
ROBERTS, PH
中科院分区：
文献类型：
--
作者：
GLATZMAIER, GA;ROBERTS, PH
我们提出了第一个三维（3D），时间依赖，自洽的磁流体动力学（MHD）方程的数值解，该方程描述了具有固体导电内核的快速旋转球形流体壳中的热对流和磁场产生。这个解决方案，作为地球发电机的粗略模拟，是一个自我维持的超临界发电机，它已经维持了三次磁扩散，大约40,000年的磁场。外核的流体速度最高可达0.4 cm s(-1)，磁场有时可达560高斯。磁能通常比维持它的对流动能大4000倍。与下面的内核和上面的地幔的粘性和磁性耦合导致它们各自的旋转速率随时间变化；地核的自转速度通常比地幔快，而且地幔日长的年代际变化与地球观测到的相似。地核-地幔边界（CMB）径向磁场的模式和振幅及其长期变化也与地球相似。纵向平均温度梯度、切变流、螺旋度和磁场的最大振幅在南北半球之间以几千年的时间尺度振荡。然而，在许多次尝试中，只有一次能量场成功地逆转了它的极性，因为内核中的能量场与大部分外核中的能量场具有相反的极性，在外核中的能量场再次改变之前，通常没有足够的时间逆转。一个成功的磁场反转发生在我们模拟的末尾。
We present the first three-dimensional (3D), time-dependent, self-consistent numerical solution of the magnetohydrodynamic (MHD) equations that describe thermal convection and magnetic field generation in a rapidly rotating spherical fluid shell with a solid conducting inner core. This solution, which serves as a crude analog for the geodynamo, is a self-sustaining supercritical dynamo that has maintained a magnetic field for three magnetic diffusion times, roughly 40000 years. Fluid velocity in the outer core reaches a maximum of 0.4 cm s(-1), and at times the magnetic field can be as large as 560 gauss. Magnetic energy is usually about 4000 times greater than the kinetic energy of the convection that maintains it. Viscous and magnetic coupling to both the inner core below and the mantle above cause time-dependent variations in their respective rotation rates; the inner core usually rotates faster than the mantle and decadal variations in the length of the day of the mantle are similar to those observed for the Earth. The pattern and amplitude of the radial magnetic field at the core-mantle boundary (CMB) and its secular variation are also similar to the Earth's. The maximum amplitudes of the longitudinally averaged temperature gradient, shear flow, helicity, and magnetic field oscillate between the northern and southern hemispheres on a time scale of a few thousand years. However, only once in many attempts does the field succeed in reversing its polarity because the field in the inner core, which has the opposite polarity to the field in most of the outer core, usually does not have enough time to reverse before the field in the outer core changes again. One successful magnetic field reversal occurs near the end of our simulation.