Evidence for periodicities in the auroral occurrence frequency since 300 AD and their implications

Spectral analyses of the Chinese auroral records dating from 300 AD using maximum entropy, Fourier and autocorrelation methods have revealed significant periods. The power spectral density of the auroral records has a strong multiplet of spectral lines centered on the median period. The prominent period is 200 years followed by enveloping bands of 80–130, 40–60 and 20–30 years. Nonstationarity is found for periods less than 120 years.The similarity of these periods with intervals between sunspot minima and other solar-terrestrial parameters is noted