Stochastic generation of MAC waves and implications for convection in Earth's core
Stochastic generation of MAC waves and implications for convection in Earth's core
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DOI：
10.1093/gji/ggx492
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发表时间：
2018-03-01
影响因子：
2.8
通讯作者：
Knezek, Nicholas
中科院分区：
文献类型：
--
作者：
Buffett, Bruce;Knezek, Nicholas
地球核心的对流可以通过各种机制维持磁Archemedes-Coriolis（MAC）波。浮力和洛仑兹力是波浪运动的可行来源，再加上磁感应的影响。我们开发了一个定量描述纬向MAC波和评估源机制，使用数值发电机模型。在发电机模型可达到的条件下，最大的来源是浮力和磁感应。然而，当这些来源外推到地球核心的预期条件时，洛伦兹力成为主要的产生机制。当内部磁场的特征是无量纲Elsasser数大约为λ，近似为10，均方根对流速度定义的磁雷诺数为Rm，近似为10时，预计该源产生的波速大约为2 km/yr（-1）（3）。我们的首选模型具有径向变化的分层和恒定（径向）背景磁场。它预测了一个广泛的功率谱的波速与大多数功率分布在30至100年的周期。
Convection in Earth's core can sustain magnetic-Archemedes-Coriolis (MAC) waves through a variety of mechanisms. Buoyancy and Lorentz forces are viable sources for wave motion, together with the effects of magnetic induction. We develop a quantitative description for zonal MAC waves and assess the source mechanisms using a numerical dynamo model. The largest sources at conditions accessible to the dynamo model are due to buoyancy forces and magnetic induction. However, when these sources are extrapolated to conditions expected in Earth's core, the Lorentz force emerges as the dominant generation mechanism. This source is expected to produce wave velocities of roughly 2 km yr(-1) when the internal magnetic field is characterized by a dimensionless Elsasser number of roughly Lambda approximate to 10 and the root-mean square convective velocity defines a magnetic Reynolds number of Rm approximate to 10(3). Our preferred model has a radially varying stratification and a constant (radial) background magnetic field. It predicts a broad power spectrum for the wave velocity with most power distributed across periods from 30 to 100 yr.