Geodynamo Conductivity Limits
Geodynamo Conductivity Limits
复制标题
DOI：
10.1029/2019gl082915
复制
发表时间：
2019-07-28
影响因子：
5.2
通讯作者：
Du, Zhixue
中科院分区：
文献类型：
--
作者：
Driscoll, Peter E.;Du, Zhixue
在金属中，例如在地核中，热导率和电导性被认为是相关的。在行星发电机中，这意味着一个矛盾：使感应电流和磁场变得更容易的导电性和阻碍热对流的传导热传输都应该同时增加。在这里，我们证明了这一矛盾意味着磁感应率在电导率和热导率的特定值处达到峰值，并推导出热发电机动作的低电导率和高电导率极限。作为地核电导率和温度的函数，得出了发电机状态图，该图确定了四种不同的发电机状态：无发电机、热发电机、成分发电机和热成分发电机。对地核与温度相关的电导率的估计表明，在内核成核之前，地球发电机可能已经接近其高电导率“无发电机”的极限，这与最近的古地磁观测一致。
In a metal, as in Earth's core, the thermal and electrical conductivities are assumed to be correlated. In a planetary dynamo this implies a contradiction: that both electrical conductivity, which makes it easier to induce current and magnetic field, and conductive heat transport, which hinders thermal convection, should increase simultaneously. Here we show that this contradiction implies that the magnetic induction rate peaks at a particular value of electrical and thermal conductivity and derive the low- and high-conductivity limits for thermal dynamo action. A dynamo regime diagram is derived as a function of electrical conductivity and temperature for Earth's core that identifies four distinct dynamo regimes: no dynamo, thermal dynamo, compositional dynamo, and thermocompositional dynamo. Estimates for the temperature-dependent electrical conductivity of the core imply that the geodynamo may have come close to its high-conductivity "no dynamo" limit prior to inner core nucleation, consistent with recent paleomagnetic observations.