High medieval auroral incidence over China and Japan: Implications for the medieval site of the geomagnetic pole

The catalog of historical oriental aurorae compiled by Keimatsu lists 116 aurorae from China and 31 aurorae from Japan in the period 801 to 1400 AD. The two listings have no events in common. If they are considered as independent random samples from the same population, the lack of overlapping events can be used to determine the probabilities of different medieval auroral occurrence frequencies over the China-Japan quarter. We find that there is a 95 percent probability that the average rate exceeded the inferred present rate by more than a factor of 20. This corresponds to a geomagnetic pole located in the Eastern Hemisphere displaced more than 9 degrees from the geographic pole.