The Geomagnetic Field during the past Million Years

地磁场是地球环境的一个重要组成部分，它可以屏蔽宇宙射线，保护地球大气层不受太阳风的影响。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对流和成分对流影响的动力过程。来自熔岩流和沉积物的古地磁数据将用于研究地磁场的长期结构和时间变化，这些数据被认为可能反映核-幔边界的热或成分地理非均质性以及外核过程。如果这种非均质性存在，它们很可能控制着地球动力学的性质，并为理解具有广泛地球物理意义的地球深部过程提供重要的见解。古地磁资料还提供了研究与地磁偏移和反转相关的特定条件的手段，并评估这些事件是否与不同的地磁过程有关。对过去十年积累的数据的仔细评估对早期关于古长期变化的观点提出了挑战，这可能对数值地球动力学模型的基础真实性很重要，并为岩心动力学提供相应的见解。将采用两种不同的策略：第一种是熔岩流数据，它具有不均匀的地理和时间采样，但适合统计建模；第二种是从沉积物中获得的时间序列数据，迄今为止缺乏可靠的强度校准，并且可能受到时间平滑或未记录的沉积物积累时间变化的影响。研究者提出以下建议：1 .更新和评估全球熔岩数据汇编，提高地理覆盖；通过适当的时空重采样，构建过去百万年的时均磁场模型；3. 采用基于古地磁功率谱的参数化模型，将时间协方差纳入古长期变化统计模型；4. 建立0 ~ 1 Ma有限分辨率时变地磁场模型；5. 研究更详细的地磁漂移和最近的反转的时变场模型；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.