Understanding the origin of the Earth's magnetic field remains one of the most challenging problems in Earth Science, a problem that is central to understanding the dynamics of the Earth's deep interior and its interactions with other parts of the Earth system. Recent years have seen great advances on two separate fronts in our understanding of the origin of the field. First, numerical geodynamo modeling has progressed to the point where numerical models generate magnetic fields of similar morphology and temporal behavior to the Earth's field. Second, the combination of a new generation of satellite magnetic field measurements and advances in geomagnetic field modeling are providing new observational insight into the geodynamo process. But, these two approaches exist in large part in isolation from one another. A collaborative research is necessary to integrate these approaches: assimilating geomagnetic observations into core dynamo modeling to (1) understand better and forecast variations of the geomagnetic field, and to (2) provide additional insight into the dynamics of magnetic field generation in the core. In this project, a data assimilation system will be defined and developed with the MoSST core dynamics model (a modular and scalable model) and observations of the geomagnetic field. The proposed system is based on the ensemble Kalman filter (EnsKF) which is an optimal assimilation method to estimate the forecast error covariance from an ensemble of forecasts. This method eliminates the need to develop an adjoint of the dynamo model, and reduces the computational cost of calculating the error covariances. The intellectual merits of the proposed research include (1) the first-ever assimilation system in geomagnetic/geodynamo field; (2) prediction of changes in Earth's magnetic environment with surface observation and numerical core dynamics model. The broader impacts of the proposed research include (1) application of geomagnetic observations to numerical dynamo modeling research; (2) application of core dynamics to geomagnetic field modeling research; (3) application of core dynamics research to other geophysical studies, e.g. Earth's rotation variation and time variable gravity field; (4) new education/training project in geomagnetic assimilation
