Global characteristics of geomagnetic field reversals from data and numerical simulations

了解地磁场反转记录的可变性是优先方案DeepDyn的一个中心方面，该方案旨在了解整个地质历史中地球深部内部的演变。然而，为了充分理解完全反转和短暂偏移的反转记录和统计特性，有时还包括全球完全反转的磁场方向，还需要更好地理解磁极变化的基本过程。球谐基函数的基础上的全球模型提供了可能性，研究全球性的极性转变期间的磁场性质。所发现的特征可以直接与数值模拟的结果进行比较，数值模拟是基于对驱动地球发电机的物理过程和力平衡的考虑。随着越来越多的古地磁记录，无论是从沉积物钻孔岩心和熔岩序列，产生在世界各地的古地磁实验室，全球模型最近已开发的Laschamps（41 000年前）和挪威-格陵兰盆地（约1000年前）。65000年前）的短途旅行，以及Matuyama-Brunhes逆转的新模型（约。距今78万年，正在建设中。在这里，我们将开发第一个全球模型的高斯-松山逆转（约。2.6百万年前）。与现有的模型一起，这将使我们能够研究至少四个事件之间的相似性和差异，即两个完全逆转和两个偏移，并提供了一个很好的理解一些最近的磁场极性变化的强大的统计特性。越来越多的具有不同参数和有或没有边界约束的数值地球发电机模拟，例如，模拟从地震层析成像模型推断的预期核幔边界热通量不均匀性，具有反转和偏移。我们将对在大范围模拟中发现的极性变化的不同特征进行系统研究。通过这些结果与基于数据的模型结果的比较，我们将更好地理解所研究的真实的事件背后的物理过程以及下地幔对地球发电机的影响。

Understanding variabilities in the geomagnetic field reversal record is a central aspect in the priority programme DeepDyn, that aims at understanding Earth’s deep interior evolution throughout the geological history. However, to fully understand the reversal record and statistical properties of full reversals and short-lived excursions, which also sometimes include globally fully reversed field directions, a better understanding of the underlying processes of magnetic polarity changes is also necessary. Global models based on spherical harmonic basis functions offer the possibility to study global properties of the magnetic field during polarity transitions. The found characteristics can be directly compared to results from numerical simulations, which are based on considerations of the physical processes and force balances that drive the geodynamo. With the growing numbers of paleomagnetic records, both from sediment drill cores and lava sequences that are produced in paleomagnetic laboratories worldwide, global models have recently been developed for the Laschamps (41 000 years ago) and Norwegian-Greenland Basin (ca. 65 000 years ago) excursions, and a new model for the Matuyama-Brunhes reversal (ca. 780 000 years ago) is under construction. Here, we will develop the first global model of the Gauss-Matuyama reversal (ca. 2.6 million years ago). Together with the existing models this will enable us to study similarities and differences between at least four events, i.e. two full reversals and two excursions and provide a good understanding of robust statistical properties of some of the most recent magnetic field polarity changes. A growing number of numerical geodynamo simulations with different parameters and with or without boundary constraints, that e.g. mimic expected core-mantle boundary heat flux heterogeneities as inferred from seismic tomography models have reversals and excursions. We will perform a systematic study of different characteristics of polarity changes found in a large range of simulations. By comparisons between these and the results from the data based models we will gain a better understanding of the physical processes underlying the studied real events and the influence of the lower mantle on the geodynamo.