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Register a new userThe Dalton Minimum and John Daltons Auroral Observations
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In addition to the regular Schwabe cycles of approximately 11 y, prolonged solar activity minima have been identified through the direct observation of sunspots and aurorae, as well as proxy data of cosmogenic isotopes. Some of these minima have been regarded as grand solar minima, which are arguably associated with the special state of the solar dynamo and have attracted significant scientific interest. In this paper, we review how these prolonged solar activity minima have been identified. In particular, we focus on the Dalton Minimum, which is named after John Dalton. We review Daltons scientific achievements, particularly in geophysics. Special emphasis is placed on his lifelong observations of auroral displays over approximately five decades in Great Britain. Daltons observations for the auroral frequency allowed him to notice the scarcity of auroral displays in the early 19th century. We analyze temporal variations in the annual frequency of such displays from a modern perspective. The contemporary geomagnetic positions of Daltons observational site make his dataset extremely valuable because his site is located in the sub-auroral zone and is relatively sensitive to minor enhancements in solar eruptions and solar wind streams. His data indicate clear solar cycles in the early 19th century and their significant depression from 1798 to 1824. Additionally, his data reveal a significant spike in auroral frequency in 1797, which chronologically coincides with the lost cycle that is believed to have occurred at the end of Solar Cycle 4. Therefore, John Daltons achievements can still benefit modern science and help us improve our understanding of the Dalton Minimum.
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In addition to regular Schwabe cycles (~ 11 years), solar activity also shows longer periods of enhanced or reduced activity. Of these, reconstructions of the Dalton Minimum provide controversial sunspot group numbers and limited sunspot positions, partially due to limited source record accessibility. We analysed Stephan Prantners sunspot observations from 1804--1844, the values of which had only been known through estimates despite their notable chronological coverage during the Dalton Minimum. We identified his original manuscript in Stiftsarchiv Wilten, near Innsbruck, Austria. We reviewed his biography (1782--1873) and located his observational sites at Wilten and Waidring, which housed the principal telescopes for his early and late observations: a 3.5-inch astronomical telescope and a Reichenbach 4-feet achromatic erecting telescope, respectively. We identified 215 days of datable sunspot observations, which are twice as much data as his estimated data in the existing database (= 115 days). Prantner counted up to 7--9 sunspot groups per day and measured sunspot positions, which show their distributions in both solar hemispheres. These results strikingly emphasise the difference between the Dalton Minimum and the Maunder Minimum as well as the similarity between the Dalton Minimum and the modern solar cycles.
The Maunder Minimum (1645-1715) is currently considered the only grand minimum within telescopic sunspot observations since 1610. During this epoch, the Sun was extremely quiet and unusually free from sunspots. However, despite reduced frequency, candidate aurorae were reported in the mid-European sector during this period and have been associated with occurrences of interplanetary coronal mass ejections (ICMEs), whereas some of them have been identified as misinterpretations. Here, we have analysed reports of candidate aurorae on 1 June 1680 with simultaneous observations in mid-Europe, and compared their descriptions with visual accounts of early modern aurorae. Most contemporary sunspot drawings from 22, 24, and 27 May 1680 have shown that this apparent sunspot may have been a source of ICMEs, which caused the reported candidate aurorae. On the other hand, its intensity estimate shows that the magnetic storm during this candidate aurora was probably within the capability of the storms derived from the corotating interaction region (CIR). Therefore, we accommodate both ICMEs and CIRs as their possible origin. This interpretation is probably applicable to the candidate aurorae in the often-cited Hungarian catalogue, on the basis of the reconstructed margin of their equatorward auroral boundary. Moreover, this catalogue itself has clarified that the considerable candidates during the MM were probably misinterpretations. Therefore, frequency of the auroral visibility in Hungary was probably lower than previously considered and agree more with the generally slow solar wind in the existing reconstructions, whereas sporadic occurrences of sunspots and coronal holes still caused occasional geomagnetic storms.
In this article, we present the results of the surveys on sunspots and auroral candidates in Rikkokushi, Japanese Official Histories from the early 7th century to 887 to review the solar and auroral activities. In total, we found one sunspot record and 13 auroral candidates in Rikkokushi. We then examine the records of the sunspots and auroral candidates, compare the auroral candidates with the lunar phase to estimate the reliability of the auroral candidates, and compare the records of the sunspots and auroral candidates with the contemporary total solar irradiance reconstructed from radioisotope data. We also identify the locations of the observational sites to review possible equatorward expansion of auroral oval. These discussions suggest a major gap of auroral candidates from the late 7th to early 9th century, which includes the minimum number of candidates reconstructed from the radioisotope data, a similar tendency as the distributions of sunspot records in contemporary China, and a relatively high magnetic latitude with a higher potential for observing aurorae more frequently than at present.
Auroral records found in historical archives and cosmogenic isotopes found in natural archives have served as sound proxies of coronal mass ejections (CMEs) and solar energetic particles (SEPs), respectively, for dates prior to the onset of telescopic sunspot observations in 1610. These space weather events constitute a significant threat to a modern civilization, because of its increasing dependency on an electronic infrastructure. Recent studies have identified multiple extreme space weather events derived from solar energetic particles (SEPs) in natural archives, such as the event in 660 BCE. While the level of solar activity around 660 BCE is of great interest, this had not been within the coverage of the hitherto-known datable auroral records in historical documents that extend back to the 6th century BCE. Therefore, we have examined Assyrian astrological reports in the 8th and 7th centuries BCE, identified three observational reports of candidate aurorae, and dated these reports to approximately 680 BCE -- 650 BCE. The Assyrian cuneiform tablets let us extend the history of auroral records and solar activity by a century. These cuneiform reports are considered to be the earliest datable records of candidate aurorae and they support the concept of enhanced solar activity suggested by the cosmogenic isotopes from natural archives.
The importance of the investigation of magnetic superstorms is not limited to academic interest, because these superstorms can cause catastrophic impact on the modern civilisation due to our increasing dependency on technological infrastructure. In this context, the Carrington storm in September 1859 is considered as a benchmark of observational history owing to its magnetic disturbance and equatorial extent of the auroral oval. So far, several recent auroral reports at that time have been published but those reports are mainly derived from the Northern Hemisphere. In this study, we analyse datable auroral reports from South America and its vicinity, assess the auroral extent using philological and astrometric approaches, identify the auroral visibility at - 17.3{deg} magnetic latitude and further poleward and reconstruct the equatorial boundary of the auroral oval to be 25.1{deg} +/- 0.5{deg} in invariant latitude. Interestingly, brighter and more colourful auroral displays were reported in the South American sector than in the Northern Hemisphere. This north-south asymmetry is presumably associated with variations of their magnetic longitude and the weaker magnetic field over South America compared to the magnetic conjugate point and the increased amount of magnetospheric electron precipitation into the upper atmosphere. These results attest that the magnitude of the Carrington storm indicates that its extent falls within the range of other superstorms, such as those that occurred in May 1921 and February 1872, in terms of the equatorial boundary of the auroral oval.
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