SUMMARY

In a rapidly rotating Boussinesq fluid, buoyant anomalies radiate low-frequency inertial wave packets that disperse along the rotation axis. The wave packets lead to axially elongated vortices, which propagate negative (positive) kinetic helicity upwards (downwards) with respect to the rotation vector. The kinetic helicity carried by the inertial wave packets is near-maximal relative to the velocity and vorticity fields. In classical mean-field theory, kinetic helicity is often associated with the α-effect, which is thought to be an important ingredient for planetary dynamos. The modification of inertial wave packets in the presence of a transverse uniform magnetic field is investigated here, motivated by small-scale dynamics in planetary cores, where a large-scale magnetic field affects fluid motions. We study numerically the dispersion of wave packets from an isolated buoyant source and from a random layer of buoyant anomalies, while varying the Lehnert number Le—the ratio of the frequencies of Alfvén and inertial waves. We find that for Le < 0.1, the vortices are columnar and continue to segregate kinetic helicity so that it is negative (positive) above (below) the buoyant source. Importantly, the wave packets induce an α-effect, which remains strong and coherent for Earth-like values of the Lehnert number (Le < 0.1). The interaction of wave packets emitted by multiple neighbouring buoyant sources results in an α-effect that is stronger than the α-effect induced by wave packets launched from an isolated buoyant source, and we provide an analytical explanation for this. The coherence of the α-effect induced by the wave packets, for Earth-like values of the Lehnert number, lends support to the α² dynamo model driven by helical waves.

中文翻译：

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关于科里奥利电磁波包的螺旋特性和感应电动势

概要

在快速旋转的Boussinesq流体中，浮力异常辐射出沿旋转轴分散的低频惯性波包。波包导致轴向伸长的涡旋，其相对于旋转矢量向上（向下）传播负（正）动力学螺旋。相对于速度场和涡度场，惯性波包所携带的动能螺旋度接近最大。在经典平均场理论中，动力学螺旋通常与α效应有关，α效应被认为是行星动力的重要组成部分。在此，研究了在横向均匀磁场存在下惯性波包的修改，这是受行星芯中的小规模动力学影响的，其中大范围的磁场会影响流体运动。Le —Alfvén和惯性波的频率之比。我们发现，对于Le <0.1，涡旋呈柱状，并继续分离动力学螺旋，因此在浮力源上方（下方）为负（正）。重要的是，波包会产生α效应，对于像勒纳特数（Le <0.1）的类地值保持强且连贯。多个相邻浮力源发出的波包的相互作用产生的α效应要比从孤立的浮力源发射的波包引起的α效应更强，为此我们提供了分析解释。由波包诱导，对于地球样的Lehnert数的值的α效应的连贯性，支持了该α ² 螺旋波驱动的发电机模型。