A magnetic storm around 1859 September 2, caused by a so-called Carrington flare, was the most intense in the history of modern scientific observations, and hence is considered to be a benchmark event concerning space weather. The magnetic storm caused worldwide observations of auroras, even at very low latitudes, such as Hawaii, Panama, or Santiago. Available magnetic-field measurements at Bombay, India, showed two peaks: the main was the Carrington event, which occurred in day time in East Asia; a second storm after the Carrington event occurred at night in East Asia. In this paper, we present results from surveys of aurora records in East Asia, which provide new information concerning the aurora activity of this important event. We found some new East Asian records of low-latitude aurora observations caused by a storm which occurred after the Carrington event. The size of the aurora belt of the second peak of the Carrington magnetic storm was even wider than that of usual low-latitude aurora events.

Dim red aurora at low magnetic latitudes is a visual and recognized manifestation of geomagnetic storms. The great low-latitude auroral displays seen throughout East Asia on 16-18 September 1770 are considered to manifest one of the greatest storms. Recently found 111 historical documents in East Asia attest that these low-latitude auroral displays were succeeding for almost 9 nights during 10-19 September 1770 in the lowest magnetic latitude areas (< 30°). This suggests that the duration of the great magnetic storm is much longer than usual. Sunspot drawings from 1770 reveals the fact that sunspots area was twice as large as those observed in another great storm of 1859, which substantiates this unusual storm activities in 1770. These spots likely ejected several huge, sequential magnetic structures in short duration into interplanetary space, resulting in spectacular world-wide aurorae in mid-September 1770. These findings provide new insights about the history, duration, and effects of extreme magnetic storms that may be valuable for those who need to mitigate against extreme events.Main Text:

Extremely bright aurora was witnessed in East Asia on 17 September 1770, according to historical documents. The aurora was described as “as bright as a night with full moon” at magnetic latitude of 25°. The aurora was dominated by red color extending from near the horizon up beyond the polar star (corresponding to elevation angle of ~35°). We performed a two‐stream electron transport code to calculate the volume emission rates at 557.7 nm (OI) and 630.0 nm (OI). Two types of distribution of precipitating electrons were assumed. The first one is based on the unusually intense electron flux measured by the DMSP satellite in the March 1989 storm. The distribution consists of hot (peaking at 3 keV) and cold (peaking at 71 eV) components. The second one is the same as the first one, but the hot component is removed. We call this high‐intensity low‐energy electrons (HILEEs). The first spectrum results in an auroral display with a bright, lower green border. The second one results in red‐dominated aurora extending up to the elevation angle of 35° when the equatorward boundary of the electron precipitation is located at 32° invariant latitude. The poleward boundary of the precipitation would be 42° invariant latitude or greater to explain the auroral display extending from near the horizon. The origin of the HILEEs is probably the plasma sheet or the plasmasphere that is transported earthward to L ~ 1.39 due to enhanced magnetospheric convection. Local heating or acceleration is also plausible.

Recently, a significant carbon-14 enhancement in the year 994 in tree rings has been found, suggesting an extremely large cosmic ray flux event during a short period. The origin of this particular cosmic ray event has not been confirmed, but one possibility is that it is of solar origin.Contemporary historical records of low latitude auroras can be used as supporting evidence for intense solar activity around that time. We investigated the previously reported as well as the new records found in contemporary observations from the 990s to determine potential auroras. Records of potential red auroras in the late 992 and early 993 were found around the world, i.e. in the Korean Peninsula, Germany, and the Island of Ireland, suggesting the occurrence of an intense geomagnetic storm driven by solar activity.2

People have probably been watching the sky since the beginning of human history. Observers in pre-telescopic ages recorded anomalous events and these astronomical records in the historical documents provide uniquely valuable information for modern scientists. Records with drawings are particularly useful, as the verbal expressions recorded by pre-telescopic observers, who did not know the physical nature of the phenomena, are often ambiguous. However, drawings for specific datable events in the historical documents are much fewer than the verbal records. Therefore, in this paper, we show the possible earliest drawings of datable auroras and a two-tail comet in a manuscript of the Chronicle of Zūqnīn, a Syriac chronicle up to 775/776 CE to interpret their nature. They provide not only the historical facts in the realm around Amida but also information about low-latitude aurora observations due to extreme space weather events and the existence of sun-grazing comets.