Quasi-geostrophic dynamo theory
Quasi-geostrophic dynamo theory
复制标题
DOI：
10.1016/j.pepi.2017.05.001
复制
发表时间：
2018-03-01
影响因子：
2.3
通讯作者：
Calkins, Michael A.
中科院分区：
文献类型：
--
作者：
Calkins, Michael A.
讨论了平面层中快速旋转对流驱动发电机的渐近理论。这些准地转发电机的一个关键特征是，洛伦兹力在量级上与科里奥利力的地转分量相当，而不是产生地转的阶分量。这一特征与行星发电机和数值发电机的观测结果一致，其中传统的Elssasser数Lambda(T) = O(1)。因此，虽然目前的数值发电机模拟无法模拟被认为是行星内部特征的强烈湍流，但有人认为，只要惯性和粘性力相对于阶科里奥利力都很小，它们就处于适当的地转平衡状态。讨论了四种不同的准地转发电机状态，每个状态都具有独特的磁动能密度比和不同的动力学特性。对于这种准地转发电机，由于洛伦兹力引起的轴向转矩显示为渐近小，这表明“泰勒约束”代表了快速旋转发电机中主力平衡的模糊度量。(C) 2017 Elsevier B.V.版权所有
The asymptotic theory of rapidly rotating, convection-driven dynamos in a plane layer is discussed. A key characteristic of these quasi-geostrophic dynamos is that the Lorentz force is comparable in magnitude to the ageostrophic component of the Coriolis force, rather than the leading order component that yields geostrophy. This characteristic is consistent with both observations of planetary dynamos and numerical dynamo investigations, where the traditional Elssasser number, Lambda(T) = O(1). Thus, while numerical dynamo simulations currently cannot access the strongly turbulent flows that are thought to be characteristic of planetary interiors, it is argued that they are in the appropriate geostrophically balanced regime provided that inertial and viscous forces are both small relative to the leading order Coriolis force. Four distinct quasi-geostrophic dynamo regimes are discussed, with each regime characterized by a unique magnetic to kinetic energy density ratio and differing dynamics. The axial torque due to the Lorentz force is shown to be asymptotically small for such quasi-geostrophic dynamos, suggesting that 'Taylor's constraint' represents an ambiguous measure of the primary force balance in a rapidly rotating dynamo. (C) 2017 Elsevier B.V. All rights reserved.