New sunspots and aurorae in the historical Chinese text corpus? Comments on uncritical digital search applications

We review some applications of the method of electronic searching for historical observations of sunspots and aurorae in the Chinese text corpus by Hayakawa et al. (, , , ), Kawamura et al. (), and Tamazawa et al. (). However, we show strong shortcomings in the digital search technique as applied by them: almost all likely true sunspot and aurora records were presented earlier (e.g., Xu et al. ), which are not mentioned in those papers; the remaining records are dubious and often refer to other phenomena, neither spots nor aurorae (this also applies to Hayakawa et al. ). The alleged aurorae in Hayakawa et al. () and Kawamura et al. () show a broad peak around full moon, not expected for aurorae. Hayakawa et al. () use the Korean report At night, the gate of heaven was opened (between AD 992 Dec 6 and AD 993 Jan 25, i.e., close to the C-14 variation AD 993/994) to estimate the Dst index of solar activity, even though the text does not fulfill any discriminative aurora criteria (except night-time). Most of the above publications include very few Chinese texts and translations, and their tables with abbreviated keywords do not allow the reader to consider alternative interpretations (the tables also do not specify which records mention night-time). We have compared some of their event tables with previously published catalogues and found various discrepancies. There are also intrinsic inconsistencies, misleading information (lunar phase for day-time events), and dating errors. We present Chinese texts and translations for some of their presumable new aurorae: only one can be considered a likely true aurora (AD 604 Jan); some others were selected on the sole basis of the use of the word light or rainbow. Several alleged new aurorae present observations beside the Sun during day-time. There are well-known comets among their presumable aurorae. We also discuss (a) whether heiqi ri pang can stand for black spot(s) on one side of or beside the sun, (b) the aurora color confusion in Hayakawa et al. (, ), and (c) whether white and unusual rainbows can be aurorae.