Spatial And Temporal Changes Of The Geomagnetic Field: Insights From Forward And Inverse Core Field Models

TL;DR

This paper reviews observational constraints and modeling approaches for understanding the Earth's geomagnetic field changes across various timescales, emphasizing uncertainties, data interpretation, and the need for advanced models and data assimilation techniques.

Contribution

It provides a comprehensive review of geomagnetic field change modeling, discusses uncertainties in data and models, and highlights future directions for numerical simulations and data assimilation.

Findings

Uncertainties in Gauss coefficients affect field change interpretations.

Apparent periodicity in secular acceleration may be an artifact.

Magnetic energy at large scales exceeds kinetic energy, guiding future models.

Abstract

Observational constraints on geomagnetic field changes from interannual to millenial periods are reviewed, and the current resolution of field models (covering archeological to satellite eras) is discussed. With the perspective of data assimilation, emphasis is put on uncertainties entaching Gauss coefficients, and on the statistical properties of ground-based records. These latter potentially call for leaving behind the notion of geomagnetic jerks. The accuracy at which we recover interannual changes also requires considering with caution the apparent periodicity seen in the secular acceleration from satellite data. I then address the interpretation of recorded magnetic fluctuations in terms of core dynamics, highlighting the need for models that allow (or pre-suppose) a magnetic energy orders of magnitudes larger than the kinetic energy at large length-scales, a target for future numerical simulations of the geodynamo. I finally recall the first attempts at implementing geomagnetic data assimilation algorithms.