The Geomagnetic Field during the past Million Years

地磁场是地球环境的重要组成部分，起着屏蔽宇宙射线和保护地球大气免受太阳风的作用。内部磁场由地球发电机维持，地球发电机是指地球液态外核中受热力和成分对流影响的动态过程。来自熔岩流和沉积物的古地磁数据将被用来研究地磁场的长期结构和时间变化，这被认为可能反映出核-地幔边界上的热或成分地理不均一性以及外核过程。如果存在这种非均质性，它们很可能控制着地球发电机的性质，并为理解地球物理感兴趣的深部过程提供了重要的洞察力。古地磁数据还提供了研究与地磁漂移和逆转有关的具体条件的手段，并评估这些事件是否与不同的核心过程有关。对过去十年积累的数据的仔细评估对早先关于古分子变化的观点提出了挑战，这可能被证明对数值地球发电机模型的地面真实情况很重要，并为核心动力学提供了相应的洞察。将采用两种不同的策略：第一种是针对地理和时间采样不均匀但可以进行统计建模的熔岩流数据；第二种是从沉积物获得的时间序列数据，迄今为止，这些数据缺乏可靠的强度校准，可能受到时间平滑或沉积物积累中未记录的时间变化的影响。研究人员提出了以下建议：1.更新和评估全球熔岩数据汇编，以提高地理覆盖率；2.构建过去100万年的时间平均磁场模型，并进行适当的时间和空间重新采样；3.使用基于古地磁功率谱的参数模型，将时间协方差包括在古分子变化的统计模型中；4.建立0-1 Ma的有限分辨率时变地磁场模型；5.研究地磁漂移和最近逆转的更详细的时变场模型；6.使用上述活动的结果来评估发电机过程。

The geomagnetic field is an important part of Earth's environment, serving as a shield from cosmic rays and protecting Earth's atmosphere from the solar wind. The internal field is maintained by the geodynamo, the name given to dynamical processes in Earth's liquid outer core that are influenced by thermal and compositional convection. Paleomagnetic data from lava flows and sediments will be used to study long term structure and temporal change of the geomagnetic field, which are considered likely to reflect thermal or compositional geographical heterogeneities on the core-mantle boundary, as well as outer core processes. It is probable that, if such heterogeneities exist, they control the nature of the geodynamo and provide important insight for understanding deep-earth processes of broad geophysical interest. Paleomagnetic data also provide the means to study specific conditions associated with geomagnetic excursions and reversals and assess whether these events relate to distinct core processes. Careful assessment of data accumulated over the past decade has generated challenges to earlier views about paleosecular variation, that may prove important for ground-truth of numerical geodynamo models and give corresponding insight for core dynamics.Two distinct strategies will be exploited: the first is for lava flow data which have uneven geographic and temporal sampling but are amenable to statistical modeling; the second is for times series of data acquired from sediments, which have so far lacked reliable intensity calibrations, and may suffer from temporal smoothing or from undocumented temporal variations in sediment accumulation. The investigators propose the following:1. Update and assess the global lava data compilation for improved geographic coverage;2. Construct time-averaged magnetic field models for the past million years with appropriate temporal and spatial resampling; 3. Use a parametric model based on the paleomagnetic power spectrum to include temporal covariance in statistical models for paleosecular variation; 4. Construct a limited resolution time varying geomagnetic field model for 0-1 Ma; 5. Investigate more detailed time varying field models for geomagnetic excursions and the most recent reversal; 6. Use results from the foregoing activities to evaluate dynamo processes.