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Comprehensive catalogues of ancient sunspot and auroralobservations from East Asia are used to identify possible intense historicalgeomagnetic storms in the interval 210 BC-AD 1918. There are about 270entries in the sunspot catalogue and about 1150 entries in the auroralcatalogue. Special databases have been constructed in which the scientificinformation in these two catalogues is placed in specified fields. For thepurposes of this study, an historical geomagnetic storm is defined in termsof an auroral observation that is apparently associated with a particularsunspot observation, in the sense that the auroral observation occurredwithin several days of the sunspot observation. More precisely, a selectioncriterion is formulated for the automatic identification of such geomagneticstorms, using the oriental records stored in the sunspot and auroraldatabases. The selection criterion is based on specific assumptions aboutthe duration of sunspot visibility with the unaided eye, the likely range ofheliographic longitudes of an energetic solar feature, and the likely rangeof transit times for ejected solar plasma to travel from the Sun to theEarth. This selection criterion results in the identification of nineteenputative historical geomagnetic storms, although two of these storms arespurious in the sense that there are two examples of a single sunspotobservation being associated with two different auroral observationsseparated by more than half a (synodic) solar rotation period. The literaryand scientific reliabilities of the East Asian sunspot and auroral recordsthat define the nineteen historical geomagnetic storms are discussed indetail in a set of appendices. A possible time sequence of events ispresented for each geomagnetic storm, including possible dates for both thecentral meridian passage of the sunspot and the occurrence of the energeticsolar feature, as well as likely transit times for the ejected solar plasma.European telescopic sunspot drawings from the seventeenth century are alsoused to assess the credibility of some of the later historical geomagneticstorms defined solely by the East Asian sunspot and auroral records. Thesedrawings cast doubt on a few of the associations between sunspot and auroralobservations based entirely on the oriental records, at least to the extentthat the occidental drawings provide a more realistic date for centralmeridian passage of the sunspot actually associated with a particularauroral observation. Nevertheless, on those occasions for which Europeansunspot drawings are available, the dates of all the pertinent East Asiansunspot and auroral observations are corroborated, apart from just oneChinese sunspot observation. The ancient historical observations of sunspotsand aurorae are discussed briefly in terms of modern observations of greatgeomagnetic storms

Identification of possible intense historical geomagnetic storms using combined sunspot and auroral observations from East Asia