The dynamics and excitation of torsional waves in geodynamo simulations
The dynamics and excitation of torsional waves in geodynamo simulations
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DOI：
10.1093/gji/ggt432
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发表时间：
2013-07
影响因子：
2.8
通讯作者：
R. Teed;C. Jones;S. Tobias
中科院分区：
文献类型：
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作者：
R. Teed;C. Jones;S. Tobias
快速旋转的行星核心中的主要力平衡是在科里奥利力、压力、浮力和洛伦兹力之间。这种磁转平衡导致泰勒态，其中空间平均方位洛伦兹力被迫在与旋转轴对齐的圆柱体上消失。任何偏离这种状态都会导致扭转振荡，其特征已在地球的长期变化中观察到，并被认为通过角动量守恒影响日长变化。为了研究扭转振动的动力学，我们在球壳中进行了几次三维发电机模拟。在我们的许多模拟中，我们发现扭转振荡，通过其以正确的阿尔芬速度传播来识别。我们发现波的频率、位置和传播方向受到参数选择的影响。扭转波在切线圆柱体内观察到，并且也有能力穿过它。我们的一些模拟显示核心传播时间为 4 到 6 年的波浪。我们计算了这些波的驱动项，发现雷诺力和通过洛伦兹力作用的地转对流对于驱动扭转振荡都很重要。
The predominant force balance in rapidly rotating planetary cores is between Coriolis, pressure, buoyancy and Lorentz forces. This magnetostrophic balance leads to a Taylor state where the spatially averaged azimuthal Lorentz force is compelled to vanish on cylinders aligned with the rotation axis. Any deviation from this state leads to a torsional oscillation, signatures of which have been observed in the Earth’s secular variation and are thought to influence length of day variations via angular momentum conservation. In order to investigate the dynamics of torsional oscillations, we perform several three-dimensional dynamo simulations in a spherical shell. We find torsional oscillations, identified by their propagation at the correct Alfv´en speed, in many of our simulations. We find that the frequency, location and direction of propagation of the waves are influenced by the choice of parameters. Torsional waves are observed within the tangent cylinder and also have the ability to pass through it. Several of our simulations display waves with core travel times of 4 to 6 years. We calculate the driving terms for these waves and find that both the Reynolds force and ageostrophic convection acting through the Lorentz force are important in driving torsional oscillations.