[michaelsbradley]

The mystery is already solved for more than a decade now, though more research remains to be done and understanding deepened:

Characteristics for the Occurrence of a High-Current, Z-Pinch Aurora as Recorded in Antiquity

https://plasmauniverse.info/downloadsCosmo/PerattTPSv31-2003...

Part 2:

https://plasmauniverse.info/downloadsCosmo/Peratt,et,al,TPSv...

Related publications:

https://plasmauniverse.info/NearEarth.html