论文标题
慢磁波在行星发电机中轴向偶极子形成中的作用
The role of slow magnetostrophic waves in the formation of the axial dipole in planetary dynamos
论文作者
论文摘要
通过分析球形发电机模型中的波运动，研究了行星发电机中轴向偶极子的偏好。我们的研究着重于慢磁波的作用，这些波是由洛伦兹，科里奥利和浮力（MAC）力之间的局部平衡产生的。由于已知慢波会随着磁场强度的增加而增强，因此场的模拟从小种子向饱和度成长有助于理解这些波在发电机作用中的作用。含能量量表中的轴向基团速度测量表明，磁场和浮力稍微修饰的快速惯性波在弱场下占主导地位。但是，对于满足$ |ω_m/ω_c|的强场，慢波的优势是显而易见的。 \ sim $ 0.1，其中$ω_m$和$ω_c$分别是alfvén和惯性波的频率。标识了方位角波数的MAC波窗口，其中慢波产生的螺旋性与偶极子的产生密切相关。对磁感应方程的分析表明，偶极子形成中的多型 - 螺旋场转化。最后，慢波的衰减可能导致极力驱动的地球核心的极性逆转。
The preference for the axial dipole in planetary dynamos is investigated through the analysis of wave motions in spherical dynamo models. Our study focuses on the role of slow magnetostrophic waves, which are generated from localized balances between the Lorentz, Coriolis and buoyancy (MAC) forces. Since the slow waves are known to intensify with increasing field strength, simulations in which the field grows from a small seed towards saturation are useful in understanding the role of these waves in dynamo action. Axial group velocity measurements in the energy-containing scales show that fast inertial waves slightly modified by the magnetic field and buoyancy are dominant under weak fields. However, the dominance of the slow waves is evident for strong fields satisfying $|ω_M/ω_C| \sim $ 0.1, where $ω_M$ and $ω_C$ are the frequencies of the Alfvén and inertial waves respectively. A MAC wave window of azimuthal wavenumbers is identified wherein helicity generation by the slow waves strongly correlates with dipole generation. Analysis of the magnetic induction equation suggests a poloidal--poloidal field conversion in the formation of the dipole. Finally, the attenuation of slow waves may result in polarity reversals in a strongly driven Earth's core.
