The Geomagnetic Field during the past Million Years

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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.