Extracting Spatial-Temporal Coherent Patterns in Geomagnetic Secular Variation Using Dynamic Mode Decomposition

Rapid growth of magnetic-field observations through SWARM and other satellite missions motivate new approaches to analyze it. Dynamic mode decomposition (DMD) is a method to recover spatially coherent motion with a periodic time dependence. We use this method to simultaneously analyze the geomagnetic radial field and its secular variation from CHAOS-7 at high latitudes. A total of five modes are permitted by noise levels in the observations. One mode represents a slowly evolving background state, whereas the other four modes describe a pair of waves; each wave is comprised of a complex DMD mode and its complex conjugate. The waves have periods of T-1 = 19.1 and T-2 = 58.4 years and quality factors of Q(1) = 11.0 and Q(2) = 4.6, respectively. A 60-year wave is consistent with previous predictions for zonal waves in a stratified fluid. The 20-year wave is also consistent with previous reports at high latitudes, although its nature is less clear.

Automated summary

The rapid growth of magnetic-field observations through SWARM and other satellite missions has led to the development of new approaches for their analysis. The method of dynamic mode decomposition (DMD) is used in this study to analyze the geomagnetic radial field and its secular variation at high latitudes. The analysis reveals five modes, with one representing a slowly evolving background state and the other four describing a pair of waves. These waves have periods of approximately 19.1 and 58.4 years, and their characteristics are consistent with previous predictions and reports.