Weak magnetic field changes over the Pacific due to high conductance in lowermost mantle
Weak magnetic field changes over the Pacific due to high conductance in lowermost mantle
复制标题
由于最下地幔的高电导，太平洋上的弱磁场发生变化
作者：
M. Dumberry;C. More
在过去的几个世纪里，太平洋地区地球磁场的时间变化一直非常低。其原因与核-幔边界附近的液态外核中的大规模流动有关，在太平洋下这种流动较弱，并且具有行星尺度的环流，这种环流是偏心的，并且广泛地避开了这一区域。然而，是什么调节这种类型的流动形态是未知的。在这里，我们提出的结果，从一个数值模型的动力学在地球的核心，其中包括电磁耦合与非均匀导电层在地幔的基础。我们发现，当这层的电导率是高于太平洋下比其他地方，较大的电磁阻力削弱了当地的核心流和偏转的行星环流远离太平洋的流动。最低地幔电导的性质仍不清楚，但分层的核心流体被困在地形起伏的核幔边界是一个可能的解释。根据地核动力学的数值模拟，太平洋下方最低地幔的高电导率使行星环流偏转，从而导致该地区磁场的变化有限。
For the past few centuries, the temporal variation in Earth’s magnetic field in the Pacific region has been anomalously low. The reason for this is tied to large-scale flows in the liquid outer core near the core–mantle boundary, which are weaker under the Pacific and feature a planetary-scale gyre that is eccentric and broadly avoids this region. However, what regulates this type of flow morphology is unknown. Here we present results from a numerical model of the dynamics in Earth’s core that includes electromagnetic coupling with a non-uniform conducting layer at the base of the mantle. We show that when the conductance of this layer is higher under the Pacific than elsewhere, the larger electromagnetic drag force weakens the local core flows and deflects the flow of the planetary gyre away from the Pacific. The nature of the lowermost mantle conductance remains unclear, but stratified core fluid trapped within topographic undulations of the core–mantle boundary is a possible explanation. High conductance in the lowermost mantle beneath the Pacific deflects the planetary gyre, which results in limited variation in the magnetic field in the region, according to numerical modelling of Earth’s core dynamics.