Global characteristics of geomagnetic field reversals from data and numerical simulations

了解地磁场逆转记录中的变化是DeepDyn优先方案的一个中心方面，该方案旨在了解地球在整个地质历史中的深部内部演化。然而，为了充分了解完全逆转和短暂漂移的逆转记录和统计特性，其中有时还包括全球完全逆转的场方向，还需要更好地了解磁极变化的基本过程。基于球谐基函数的全局模型提供了研究极性转变过程中磁场的全局性质的可能性。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。随着世界各地古地磁实验室产生的沉积物钻孔岩心和熔岩序列记录的古地磁记录越来越多，拉尚(41000年前)和挪威-格陵兰盆地(约65000年前)的全球模型最近被开发出来，一个新的松山-布鲁内斯反转(约78万年前)模型正在建造中。在这里，我们将建立第一个高斯-松山反转的全球模型(大约260万年前)。结合现有的模型，这将使我们能够研究至少四个事件之间的异同，即两次完全逆转和两次漂移，并提供对最近一些磁场极性变化的稳健统计特性的良好理解。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的核-地幔边界热通量不均匀，有反转和漂移。我们将对在大范围模拟中发现的不同的极性变化特征进行系统的研究。通过将这些结果与基于数据的模型的结果进行比较，我们将更好地了解所研究的真实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.