Sequential Modelling of the Earth's Core Magnetic Field and Surface Flow

Abstract:

Variations of the geomagnetic field are, up to now, the only source of information on the Earth’s liquid outer core flow dynamics. Modern geomagnetic field models, derived using satellite data, now cover more than twenty years. They are obtained through the processing and the analysis of a massive amount of vector magnetic data. The field measured at the surface of the Earth results from the contributions of numerous external and internal sources. Therefore, the understanding of the dynamics and physics of the geomagnetic field, in particular the core field, requires for field models to describe accurately as much of these sources as possible. This work aims at providing reliable models that describe the short term evolution of the core magnetic field and of the core surface flow. To address this problem, we use a sequential modelling approach (a Kalman filter), combined with a correlation based modelling step. A sequence of core field snapshot models, 3 months apart, has been built, allowing for a temporal resolution of the order of the year. The resulting time series of core field models present the general characteristics of the models based on more classic modelling techniques, thus supporting the reliability of this method. New interesting features were also found in both the core field and flow time series, especially at small spatial scales. These results suggest that our method is able to provide new, interesting information about the small time scale behaviour of the core field and the phenomena inducing its variations. They also highlight the importance of a careful calibration of the Kalman prediction and smoothing steps.