A 6-year quasi-periodicity in the geomagnetic secular acceleration pulses over 1932–2022

Abstract

Recent studies suggest that the secular variation dynamics of the geomagnetic field exhibits periodic patterns that indicate underlying wave processes in the Earth's core. However, analytical models of the core geomagnetic field based on geographically sparse and noisy observatory data have apparent limitations for studying fine structure of its spatiotemporal variations. The advent of satellite measurements of the full geomagnetic field vector in 1999 removed this limitation and made it possible to produce reliable and highly accurate models of the secular variation that allow downward continuation to the core-mantle boundary. These models have revealed rapid core field variations on a time scale of the order of 10 years. In particular, the 6-year quasi-periodicity in the second time derivative of the geomagnetic field has been discovered. In this research, we build on our previous works to extract the secular variation and secular acceleration signal from the magnetic observatory datasets over a longer period. As a result, our approach to data analysis has made it possible to confirm the existence of a 3-year quasi-periodicity of secular acceleration pulses of alternating polarity over 90-year period (1932–2022), i.e. far before the advent of the space era. The proposed methodology does not imply an intermediate production of a core field model, as done according to classical approaches.