Subdaily meteorological measurements of temperature, direction of the movement of the clouds, and cloud cover in the Late Maunder Minimum by Louis Morin in Paris

We have digitized three meteorological variables (temperature, direction of the movement of the clouds, and cloud cover) from copies of Louis Morin’s original measurements (Source: Institute of History / Oeschger Centre for Climate Change Research, University of Bern) and subjected them to quality analysis to make these data available to the scientific community. Our available data cover the period 1665–1709 (temperature beginning in 1676). We compare the early instrumental temperature dataset with statistical methods and proxy data to validate the measurements in terms of inhomogeneities and claim that they are, apart from small inhomogeneities, reliable. The Late Maunder Minimum (LMM) is characterized by cold winters and autumns, and moderate springs and summers, with respect to the reference period of 1961–1990. Winter months show a significant lower frequency of westerly direction of movement of the clouds. This reduction of advection from the ocean leads to a cooling in Paris in winter. The influence of the advection becomes apparent when comparing the last decade of the 17th century (cold) and the first decade of the 18th century (warm). A lower frequency of westerly direction of movement of the clouds can also be seen in summer, but the influence is stronger in winter than in summer. Consequently, the unusually cold winters in the LMM can be attributed to a lower frequency of westerly direction of movement of the clouds. An impact analysis reveals that the winter of 1708/09 was a devastating one with respect of consecutive ice days, although other winters are more pronounced (e.g., the winters of 1676/77, 1678/79, 1683/84, 1692/93, 1694/95 and 1696/97) in terms of mean temperature, ice 15 days, cold days or consecutive cold days. An investigation of the cloud cover data revealed a high discrepancy in the seasons, where the winter season (DJF) (−13.2 %) and the spring season (MAM) (−12.6 %) show a negative anomaly of the total cloud cover (TCC), whereas summer (JJA) (−0.5 %) shows a moderate anomaly of TCC with respect to the 30 year mean of the Meteobluedata (1985–2014).

Climatic, weather and socio-economic conditions corresponding with the mid-17th century eruption cluster

The mid-17th century is characterized by a cluster of explosive volcanic eruptions in the 1630s and 1640s, deteriorating climatic conditions culminating in the Maunder Minimum as well as political instability and famine in regions of Western and Northern Europe as well as China and Japan. This contribution investigates the sources of the eruptions of the 1630s and 1640s and their possible impact on contemporary climate using ice-core, tree-ring and historical evidence, but will also look into the socio-political context in which they occurred and the human responses they may have triggered. Three distinct sulfur peaks are found in the Greenland ice core record in 1637, 1641–42 and 1646. In Antarctica, only one unambiguous sulfate spike is recorded, peaking in 1642. The resulting bipolar sulfur peak in 1641–1642 can likely be ascribed to the eruption of Mount Parker (6° N, Philippines) on December 26, 1640, but sulfate emitted from Koma-ga-take (42° N, Japan) volcano on July 31, 1641, has potentially also contributed to the sulphate concentrations observed in Greenland at this time. The smaller peaks in 1637 and 1646 can be potentially attributed to the eruptions of Hekla (63° N, Iceland) and Shiveluch (56° N, Russia), respectively. To date, however, none of the candidate volcanoes for the mid-17th century sulphate peaks have been confirmed with tephra preserved in ice cores. Tree-ring and written sources point to severe and cold conditions in the late 1630s and early 1640s in various parts of Europe, and to poor harvests. Yet the early 17th century was also characterized by widespread warfare across Europe – and in particular the Thirty Years’ War (1618–1648), rendering any attribution of socio-economic crisis to volcanism challenging. In China and Japan, historical sources point to extreme droughts and famines starting in the late 1630s, and thus preceding the eruptions by some years. The case of the eruption cluster in the late 1630s and early 1640s and the climatic and societal conditions recorded in its aftermath thus offer a textbook example of difficulties in (i) unambiguously distinguishing volcanically induced cooling, wetting or drying from natural climate variability, and (ii) attributing political instability, harvest failure and famines solely to volcanic climatic impacts. This example shows that the impacts of past volcanism must always be studied within the contemporary socio-economic contexts, but that it is also time to most past reductive framings and sometimes reactionary oppositional stances in which climate (and environment more broadly) either is or is not deemed an important contributor to major historical events.

New possibilities of the PCA-Seq method in the analysis of time series (on the example of solar activity)

When analyzing a 1D time series, it is traditional to represent it as the sum of the trend, cyclical components and noise. The trend is seen as an external influence. However, the impact can be not only additive, but also multiplicative. In this case, not only the level changes, but also the amplitude of the cyclic components. In the PCA-Seq method, a generalization of SSA, it is possible to pre-standardize fragments of a time series to solve this problem. The algorithm is applied to the Anderson series – a sign alternating version of the well-known Wolf series, reflecting the 22-year Hale cycle. The existence of this cycle is not disputed at high solar activity, but there are doubts about the constancy of its period at this time, as well as its existence during the epoch of low solar activity. The processing of the series by the PCA-Seq method revealed clear oscillations fluctuations of almost constant amplitude with an average period of 21.9 years, and it was found that the correlation of these oscillations with the time axis for 300 years does not differ significantly from zero. This confirms the hypothesis of the existence of 22-year oscillations in solar activity even at its minima, like the Maunder minimum.

Number of Sunspot Groups and Individual Sunspots Recorded by Tevel for the Period 1816–1836 in the Dalton Minimum

Cornelis Tevel made sunspot observations during the period 1816–1836, including the Dalton Minimum. In this work, the first revision of these observations since Wolf incorporated them into his database is presented. On the one hand, the number of individual sunspots from Tevel’s drawings was counted. This is of special interest for the sunspot number reconstruction because this kind of information is not as common in historical sunspot records as the number of groups. Thus, Tevel could be considered for the future reconstruction of the sunspot number index. On the other hand, the number of groups counted according to modern sunspot group classifications finding significant misinterpretations with the number of groups assigned to Tevel in the existing databases. Tevel was a relevant sunspot observer in the Dalton Minimum. In fact, he was the observer with the highest number of groups observed in Solar Cycles 6 and 7 according to the existing sunspot group number databases. According to the raw group number recount in this work, the maximum amplitudes for Solar Cycles 6 and 7 are, respectively, 27% and 7% lower than those previously determined. Moreover, Solar Cycle 6 is the weakest solar cycle since the Maunder Minimum after applying these new counts. Group counts from Tevel’s observations were compared with those from relevant contemporary astronomers, demonstrating that Schwabe and Tevel systematically recorded a higher number of groups than Flaugergues and Derfflinger. In addition, sunspot areas and positions recorded by Tevel should be used with caution for scientific purposes.

Climate history of the principality of Transylvania during the Maunder Minimum (MM) years (1645–1715 CE)

This paper deals with the climate in the former Grand Duchy of Transylvania, now one of the three major geographical provinces of Romania, within the so-called Maunder Minimum (MM) (1645–1715), an astrophysically defined part of the Little Ice Age (LIA), which was characterized by reduced solar activity. The historical data from Transylvania are compared with that from Germany, Austria and Switzerland. This comparison for the period 1645–1715 shows good agreement but also reveals geographic characteristics of the region. For the first time, we present here a comparison between the four geographic areas in text and tabular form. Quotes from mostly German-language sources are reproduced in English translation. Furthermore, we examine for a longer period (1500–1950) the extent to which the climate of Transylvania might have been affected by long-term fluctuations in solar activity, as deduced from isotopic reconstructions from ice cores. This comparison suggests a certain solar influence but the agreement is not very pronounced. Future investigation in a pan-European context is needed to reach reliable statements. Some results are unexpected – like an unusually small number of severe winters during the last decades of the MM, where extreme cold was restricted to a few years, like the extreme winters 1699/1700 and 1708/1709.

Aurora Observations from the Principality of Transylvania from the 16th to the 18th Century CE

We focused on the period from about 1500 CE to 1800 CE and present a compilation of 78 different auroral sightings for the period from the geographical area of the former Principality of Transylvania, then part of the Kingdom of Hungary, and we give source quotations in English translation. Of the 78 potential aurorae, 23 are missing from the catalog of Rethly and Berkes (1963) and are introduced here for the first time into the scientific discourse on past solar activity. The region of Transylvania located around 46° northern latitude is a good geographical indicator for an auroral oval extending unusually far towards the Equator. The reports of seven celestial phenomena from Transylvania during the period of the Maunder minimum (1645 – 1715), which are considered genuine northern lights at a medium to very high probability level, suggest that even during this time of greatly reduced solar activity, aurorae penetrated down to near 45° latitude. Three of these potential aurorae, however, fall within the 18th century, when the Sun was already recovering from the deep minimum phase. Comparing the distribution of potential auroral sightings in Transylvania from the 16th to the 18th century clearly shows, in comparison with other aurora catalogs and with reconstructed solar activity, that high selectivity due to the historical-source situation (incomplete chronicles, lost reports, and lack of scientific interest on the part of chroniclers) makes statements about actual long-term distributions almost impossible. Furthermore, the catalog of Rethly and Berkes is shown to be rather incomplete and to contain several doubtful entries.

Gradual onset of the Maunder Minimum revealed by high-precision carbon-14 analyses

The Sun exhibits centennial-scale activity variations and sometimes encounters grand solar minimum when solar activity becomes extremely weak and sunspots disappear for several decades. Such an extreme weakening of solar activity could cause severe climate, causing massive reductions in crop yields in some regions. During the past decade, the Sun’s activity has tended to decline, raising concerns that the Sun might be heading for the next grand minimum. However, we still have an underdeveloped understanding of solar dynamo mechanisms and hence precise prediction of near-future solar activity is not attained. Here we show that the 11-year solar cycles were significantly lengthened before the onset of the Maunder Minimum (1645–1715 CE) based on unprecedentedly high-precision data of carbon-14 content in tree rings. It implies that flow speed in the convection zone is an essential parameter to determine long-term solar activity variations. We find that a 16 year-long cycle had occurred three solar cycles before the onset of prolonged sunspot disappearance, suggesting a longer-than-expected preparatory period for the grand minimum. As the Sun has shown a tendency of cycle lengthening since Solar Cycle 23 (1996–2008 CE), the behavior of Solar Cycle 25 can be critically important to the later solar activity.