On Backus’ mantle filter theory and the 1969 geomagnetic impulse
On Backus’ mantle filter theory and the 1969 geomagnetic impulse
复制标题
巴科斯地幔过滤理论和 1969 年地磁脉冲
DOI：
10.1111/j.1365-246x.1984.tb01965.x
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发表时间：
1984
影响因子：
2.8
通讯作者：
J. Ducruix
中科院分区：
文献类型：
--
作者：
V. Courtillot;J. Mouël;J. Ducruix
概括。
我们讨论了巴科斯的地幔过滤理论与 1969 年地磁脉冲（或加加速度）的关系。巴科斯表明，谐波模式的混合可能是欧洲天文台数据中发现的平方地幔滤波器平滑时间负值的原因，这一特征对于纯内部谐波脉冲来说在数学上是不可能的。我们在这里展示并通过一个简单的数值实验来说明，这个负值可能仅仅是由于剩余的外部太阳周期效应造成的。结合1969年脉冲在全球范围内同步的观察结果，我们得出以下结论：（1）巴科斯定义的地幔滤波器的平滑时间和零频延迟很可能都短于几年； (2) 在这种情况下，在日长曲线中观察到的 1956 年肘部将与 1969 年脉冲无关； (3) 超过97%的地幔体积的电导率可能低于几百Ω-1 m-1。我们记得我们之前的建议，即磁力变化显然使日长曲线领先 10-15 年，这可以用电磁核幔耦合的布拉德模型来解释。
Summary.
We present a discussion of Backus’ mantle-filter theory in relation to the 1969 geomagnetic impulse (or jerk). Backus shows that mixing of harmonic modes may be responsible for the negative value of the squared mantle-filter smoothing time which is found with European observatory data, a feature that is not mathematically possible for a pure internal harmonic impulse. We show here, and illustrate with a simple numerical experiment, that this negative value may simply be due to a remaining external solar cycle effect. This, together with the observation that the 1969 impulse is both world-wide and synchronous, leads us to propose that: (1) the smoothing time and zero-frequency delay of the mantle filter, as defined by Backus, are both likely to be shorter than a few years; (2) in that case, the 1956 elbow observed in the length of day curve would not be related to the 1969 impulse; (3) electrical conductivity is likely to be lower than a few hundred ω-1 m-1 in more than 97 per cent of the volume of the mantle. We recall our earlier suggestion that the magnetic variations apparently lead the length of day curve by 10-15 yr, which can be accounted for in terms of a Bullard model of electromagnetic core-mantle coupling.