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

Abstract

Abstract 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 T1 = 19.1 and T2 = 58.4 years and quality factors of Q1 = 11.0 and Q2 = 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.