Can a 1-D mantle electrical conductivity model generate magnetic jerk differential time delays?
Can a 1-D mantle electrical conductivity model generate magnetic jerk differential time delays?
复制标题
一维地幔电导率模型能否产生磁急动微分时间延迟？
DOI：
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
A. Jackson
中科院分区：
文献类型：
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作者：
K. Pinheiro;A. Jackson
1969年、1978年和1991年发生的全球急变在地球表面并不是同时发生的，表现出大约两年的不同延迟。解释这种耐人寻味的时间模式的一种方法是将地幔视为导体。因此，在地球表面观测到的地磁场将对应于在核-地幔边界(CMB)产生的原始场的过滤版本。我们发展了这一问题的正演方法，假定急流的时间部分是在CMB处磁场的三阶时间导数中的同时脉冲。利用两种不同的功率谱，建立了两种冲击幅值的合成球谐模型。地幔的影响通过一个一维径向电导率模型来说明，该模型充当线性、因果和时不变的滤波器。关键是不同的谐波程度所对应的滤光片是不同的。因此，由于谐波的混合随着位置的不同而不同，地球表面将存在明显的时间延迟。利用Backus的地幔滤波理论，我们证明了一个简单的一维地幔电导率模型能够产生强烈依赖于地幔形态输入模型的差分地冲时间延迟。我们还说明了对于磁场的每个分量，时间延迟是不同的。
SUMMARY Worldwide jerks occurring in 1969, 1978 and 1991 are not simultaneous at the earth’s surface, showing differential delays of about 2 yr. One way to explain this intriguing temporal pattern is to consider the earth’s mantle as a conductor. Consequently the geomagnetic field observed at the earth’s surface will correspond to a filtered version of the original field generated at the core‐mantle boundary (CMB). We developed the forward approach to this problem assuming the temporal part of the jerk as a simultaneous impulse in the third time-derivative of the magnetic field at the CMB. Two synthetic spherical harmonic models of the jerk amplitudes are built by using two different power spectra. The effect of the mantle is illustrated by a 1-D radial electrical conductivity model that acts as linear, causal and time-invariant filter. The key point is that the mantle filter is different for each harmonic degree. Therefore, because the mixing of harmonics varies with location, distinct time delays will exist at the earth’s surface. By using Backus’ mantle filter theory, we demonstrate that a simple 1-D mantle electrical conductivity model is able to generate differential jerk time delays that depend strongly on the jerk morphology input model. We also illustrate that the time delays will vary for each component of the magnetic field.