Convection-driven kinematic dynamos at low Rossby and magnetic Prandtl numbers: Single mode solutions.
Convection-driven kinematic dynamos at low Rossby and magnetic Prandtl numbers: Single mode solutions.
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低罗斯贝数和磁普朗特数的对流驱动运动发电机：单模解决方案。
DOI：
10.1103/physreve.93.023115
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发表时间：
2016
期刊：
影响因子：
--
通讯作者：
Calkins MA
中科院分区：
文献类型：
--
作者：
Calkins MA
发电机行动的发病范围内的一个新开发的低Rossby，低磁普朗特数，对流驱动的发电机模型进行了研究。这个多尺度模型代表了平均场发电机模型的渐近精确形式，其中小尺度对流由有限振幅单模解明确表示。定常和振荡对流被认为是各种水平的平面形状。动力学螺旋度被观察到是一个单调递增的函数的瑞利数。因此，非常小的磁性普朗特数发电机可以找到足够大的瑞利数。所有的发电机被发现是振荡的振荡频率增加的对流的强度增加和磁普朗特数减少。运动发电机的行动是强烈控制的轮廓的螺旋度;单一模式的解决方案，表现出边界层的螺旋度的行为表明发电机行动的效率降低，由于在边界层区域的磁扩散的增强。对于一个给定的值的瑞利数，较低的磁普朗特数发电机被激发的情况下，振荡对流相比，稳定的对流。关于行星发电机，这些结果表明，典型的液态金属的低磁普朗特数发电机更容易驱动的热对流比成分对流。
The onset of dynamo action is investigated within the context of a newly developed low Rossby, low magnetic Prandtl number, convection-driven dynamo model. This multiscale model represents an asymptotically exact form of anmean field dynamo model in which the small-scale convection is represented explicitly by finite amplitude, single mode solutions. Both steady and oscillatory convection are considered for a variety of horizontal planforms. The kinetic helicity is observed to be a monotonically increasing function of the Rayleigh number. As a result, very small magnetic Prandtl number dynamos can be found for sufficiently large Rayleigh numbers. All dynamos are found to be oscillatory with an oscillation frequency that increases as the strength of the convection is increased and the magnetic Prandtl number is reduced. Kinematic dynamo action is strongly controlled by the profile of the helicity; single mode solutions which exhibit boundary layer behavior in the helicity show a decrease in the efficiency of dynamo action due to the enhancement of magnetic diffusion in the boundary layer regions. For a given value of the Rayleigh number, lower magnetic Prandtl number dynamos are excited for the case of oscillatory convection in comparison to steady convection. With regard to planetary dynamos, these results suggest that the low magnetic Prandtl number dynamos typical of liquid metals are more easily driven by thermal convection than by compositional convection.
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