UC Berkeley

Short-period fluctuations in the Earth’s geomagnetic field have been observed through satel- lite observations over the past 20 years. In this work, we explore the use of two data driven-techniques to quantify and interpret the short-period fluctuations. Complex empirical orthogonal functions (CEOFs) are applied to observations of the second time derivative of the geomagnetic field (secular acceleration) from several localized regions of the CHAOS6 model (Finlay et al., 2016). We found evidence of eastward and westward traveling waves with periods of 7.08 ± 0.58 and 15.73 ± 4.44 years, respectively, in the Atlantic and South Asia regions. Furthermore, we have applied dynamic mode decomposition (DMD) to investigate the temporal evolution of the radial magnetic field (Br) and secular variation (SV) at high latitudes using CHAOS7 (Finlay et al., 2020). Our results exhibit waves with periods of 19.1 and 58.4 years. A 60-year wave is compatible with prior predictions for zonal waves in a stratified fluid. The 20-year wave is consistent with previous findings at high latitudes, although the wave characteristics do not permit a simple interpretation. Finally, we study positive and negative geomagnetic acceleration patches moving westward at high latitudes. Magnetic Rossby waves offer one possible interpretation of the observations. This type of waves can account for the propagation direction and phase velocity. However, the predicted spatial pattern of the magnetic field variation is more complex than the observations. Zonal MAC waves, however, can explain the observed field with a stratified layer at the core’s top. In conclusion, these results are significant for comprehending the dynamics of the geomagnetic field and its impact on the Earth’s outer core structure.