Equatorial auroral records reveal dynamics of the paleo-West Pacific geomagnetic anomaly

Localized regions of low geomagnetic intensity such as the South Atlantic Anomaly allow energetic particles from the Van Allen radiation belt to precipitate into the atmosphere and have been linked to a signature in the form of red aurora-like airglow visible to the naked eye. Smoothed global geomagnetic models predict a lowintensity West Pacific Anomaly (WPA) during the sixteenth to nineteenth centuries characterized by a simple time dependence. Here, we link the WPA to an independent database of equatorial aurorae recorded in Seoul, South Korea. These records show a complex fluctuating behavior in auroral frequency, whose overall trend from 1500 to 1800 AD is consistent with the locally weak geomagnetic field of the WPA, with a minimum at 1650 AD. We propose that the fluctuations in auroral frequency are caused by corresponding and hitherto unknown fluctuations in the regional magnetic intensity with peaks at 1590 and 1720 AD, a time dependence that has been masked by the smoothing inherent in regularized global geomagnetic models. A physical core flow model demonstrates that such behavior requires localized time-dependent upwelling flows in the Earth's core, possibly driven by regional lower-mantle anomalies.

Automated summary

Localized regions of low geomagnetic intensity, such as the South Atlantic Anomaly, allow energetic particles from the Van Allen radiation belt to precipitate into the atmosphere, resulting in a red aurora-like airglow visible to the naked eye. Research suggests that the West Pacific Anomaly experienced low geomagnetic intensity during the sixteenth to nineteenth centuries, with complex fluctuations in auroral frequency associated with time-dependent upwelling flows in the Earth's core, potentially driven by regional lower-mantle anomalies. This behavior has been masked by the smoothing effects of regularized global geomagnetic models.