Quantifying paleosecular variation: Insights from numerical dynamo simulations
Quantifying paleosecular variation: Insights from numerical dynamo simulations
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DOI：
10.1016/j.epsl.2013.08.048
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发表时间：
2013-11-15
影响因子：
5.3
通讯作者：
Gilder, Stuart A.
中科院分区：
文献类型：
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作者：
Lhuillier, Florian;Gilder, Stuart A.
由于发电机建模的进步，现在可以产生相当于几千万年的时间段内磁极性反转的数值序列。使用一组五个数值模型，集成了相当于 40-50 迈尔的数值，我们生成了类似于从火山流中得出的古地磁数据的合成数据。我们发现方向的分布与古地磁数据库中观察到的非常相似。五个模型之间的古世间变化最好通过古强度 (epsilon(F)) 的相对变化以及精度参数 (k) 定义的方向或极点的相对分散来区分。结合这些参数可以最好地测试地球发电机过去是否在不同的状态下运行。需要大约 100 万年的时间和 200 个与时间无关的样本才能实现 epsilon(F) 和 k 的收敛。 epsilon(F) 和 k 的量与平均时间持续时间 (mu(chr)) 密切相关，这表明偏移和逆转是古世变的一个组成部分。如果适用于地球发电机，k 对 mu(chr) 的线性依赖性可以帮助在没有可用反转频率数据的地质时期预测地球的 mu(chr)；它还预测超级时间期间方向的平均 k（对于白垩纪正常超级时间，k 大约为 2500）比主动反转期间（对于最后 80 Myr，k 大约为 35）要高得多。由于没有观察到如此高的 k 值，要么该发电机模型系列不适用于地球发电机，要么在超时期间作用的地球发电机状态独立于在频繁反转期间作用的地球发电机状态。 (C) 2013 Elsevier B.V. 保留所有权利。
Thanks to advances in dynamo modelling, it is now possible to produce numerical sequences of magnetic polarity reversals over periods of time equivalent to several tens of millions of years. Using a set of five numerical models integrated over the equivalent of 40-50 Myr, we generated synthetic data analogous to paleomagnetic data derived from volcanic flows. We find that the distributions of directions are remarkably similar to those observed in the paleomagnetic database. Paleosecular variation among the five models is best discriminated by the relative variability in paleointensity (epsilon(F)) and the relative dispersion of directions or poles as defined by the precision parameter (k). Whether the geodynamo operated in different regimes in its past can be best tested with these parameters in combination. Roughly one million years of time with 200 time-independent samples is required to achieve convergence of epsilon(F) and k. The quantities epsilon(F) and k correlate well with the average chron duration (mu(chr)), which suggests that excursions and reversals are an integral part of paleosecular variation. If applicable to the geodynamo, the linear dependence of k on mu(chr) could help to predict mu(chr) for the Earth during geologic times with no available reversal frequency data; it also predicts much higher average k for directions during superchrons (k approximate to 2500 for the Cretaceous normal superchron) than during actively reversing times (k approximate to 35 for the last 80 Myr). As such high k values are not observed, either this family of dynamo models is not applicable to the geodynamo, or the geodynamo regime acting during superchrons is independent of that acting during times with frequent reversals. (C) 2013 Elsevier B.V. All rights reserved.