Abstract Understanding the Earth's magnetic field evolution requires examining the fluid flow at the core‐mantle boundary that drives the changes over different timescales. The inversion process to derive core‐surface flow velocities from secular variation data encounters non‐uniqueness issues, necessitating a priori assumptions that yield different flow solutions. In this work, we investigate the Earth's core‐surface flows over the last 3,300 years using the SHAWQ‐family archeomagnetic model (Campuzano et al., 2019, https://doi.org/10.1016/j.epsl.2019.01.050 ; Osete et al., 2020, https://doi.org/10.1016/j.epsl.2019.116047 ) to invert for time‐dependent purely toroidal and tangentially geostrophic solutions. We apply the constraints as regularization terms that let us reproduce different large‐scale flows at the core surface. We evaluate the frozen‐flux hypothesis and we show that the temporal averaging range in archeomagnetic models reliably captures the long‐term behavior of core‐surface flows over time. Then, we use these core flow models to analyze different global phenomena, such as the episodes of large‐scale eastward and westward flow and the exchange of angular momentum between the fluid core and the mantle that contributes to the Length of the Day variations at millennial timescales.
Rivera et al. (Sun,) studied this question.