Response of aurora candidates in the Chinese official histories to the space climate during 511–1876

Continuous observations at specified locations and chronicling of astronomical phenomena provide a good opportunity to study ancient space weather. There are 248 white, 125 red, and 44 blue color aurora-like descriptions, also known as aurora candidates, recorded in Chinese official historical records during the 1365-year period of 511–1876. Qualitative descriptions of the color, location, and appearance time of these candidates are quantitatively denoted. The red, white, and blue aurora candidates occurred most frequently 34% in autumn, 32% in summer, and 49% in summer, respectively. The white and red aurora as well as the overall candidates tend to appear during high solar activity periods. By contrast, the blue candidates frequently occur during low solar activity periods. Statistical results with 90% confidence intervals further show that the relationship between solar activities and overall/red (white/blue) aurora candidates is significant (insignificant). The red aurora candidates that frequently occurred in autumn during the periods of high solar activity agree well with those of low/middle latitude auroras, while the white aurora candidates might be confounded by noctilucent clouds or other atmospheric optical events, such as airglows, moon halo, etc. The study of ancient space weather/climate based on historical records shows that aurora occurrences are related to solar activities, and in particular, red auroras frequently appear in low/middle latitudes during high solar activity periods. Graphical Abstract