Wolf minimum

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The wolf minimum is a period of low solar activity in the period from 1282 to 1342.

etymology

The minimum of solar activity is named after the Swiss astronomer Johann Rudolf Wolf .

introduction

The solar activity over the past 2000 years

Reconstructions of solar activity for the entire Holocene show that the sun spent around 70% in a normal state over the last 10,000 years, which is characterized by average activity. 15 to 20% of the period falls to minima with low activity and the remaining 10 to 15% to maxima with very high activity. This shows that the sun behaves irregularly and that the course of its activity cannot be described by quasi-periodic processes .

Large minima such as the Maund minimum of the late 17th century are typical solar phenomena. So far, a total of 27 such minima have been identified in the Holocene. Their temporal occurrence is not periodic, but rather suggests a chaotic course . They are arranged in clusters that are separated from one another by a 2000 to 2500 year rest period.

There are two types of large minima: short-term minima of the Maunder type and longer-term minima of the Spörer type . The temporal course of these minima can be reproduced to a certain extent by modern, stochastically driven dynamo models , but there are still some unsolved problems here.

The solar activity after 1940 was exceptionally high and corresponds to a large maximum, a typical but nevertheless very rare and irregular event in the behavior of the sun. This maximum came to an end after solar cycle 23. In contrast to large minima, the maxima resemble an irregular Poisson process .

description

14 C as an indicator of solar activity over the past 1100 years.

The wolf minimum, a longer period of below average solar activity (a minimum of the Maunder type), follows the medieval maximum , which existed between 1150 and 1300 (alternatively also a little earlier between 1100 and 1250). Usoskin (2013) gives the time span 1270 to 1340 for the Wolf minimum with a centering at 1305. After a relatively short return to negative δ 14 C values ​​(note: negative δ 14 C values ​​correlate with warmer temperatures), it came back in 1420 to a clear minimum ( Spörminimum ) and the beginning of the Little Ice Age .

Since the period is before the observation of sunspots , the minimum can only be detected indirectly through proxy data such as the 14 C content in tree rings. The measured amplitude of the minimum is around 20 ‰ δ 14 C; For example, Usoskin and colleagues (2008) find an amplitude ranging from - 12 to + 8 ‰ δ 14 C for the wolf minimum . Converted to the reconstructed number of sunspots, this amplitude corresponds to a variation of 0 to 20 or 30 sunspots for 14 C ( as a comparison: the amplitude of the sunspots for the penultimate cycle 23 was 120) and 15 to 38 for 10 Be .

parameter

anomaly Period Number of sunspots
(reconstructed)		 Radio flux density
W / m² x nm		 Solar wind
km / s
Oortminimum 1090-1140 24.00 ± 20.00 82.70 ± 32.10 406.00 ± 15.00
Medieval maximum 1140-1200 53.00 ± 38.30 112.40 ± 55.20 428.00 ± 28.70
Wolf minimum 1300-1386 0.46 ± 1.87 58.50 ± 9.60 388.30 ± 1.40
Minimum 1410-1515 0.06 ± 0.59 58.09 ± 8.20 388.00 ± 0.40
Mouth minimum 1641-1715 3.56 ± 8.72 61.70 ± 17.60 390.70 ± 6.50
Dalton minimum 1790-1825 26.10 ± 23.40 84.80 ± 36.10 407.60 ± 17.60
Modern maximum 1900-1999 57.54 ± 36.45 117.10 ± 53.20 431.10 ± 27.40

Climatic effects

Reconstructed volcanic radiative forcing from the last 2500 years. Clearly recognizable is the enormous spike of the Samalas eruption in 1257 (here marked as 1258)

The wolf minimum generally brought a cooling off for the world climate . It marked the end of the Medieval Warm Age and gradually led to the Little Ice Age.

As the parameters outlined above show, the Wolf minimum was clearer than the previous Oort Minimum and its intensity was roughly comparable to the following Spörminimum and the Maunder Minimum , whose temperatures, however, were even lower.

Interestingly, the eruption of Samala in 1257 - one of the most important volcanic eruptions of the last millennium with an enormously high sulfur input of 258 teragrams (258 × 10 12 g) sulfate aerosols into the stratosphere - is at the beginning of the wolf minimum.

In the Alps there was an advance of the glaciers . For example, the Aletsch Glacier began to advance again from 1250 and reached its peak around 1350. Similar to the Gorner Glacier , which reached its peak around 1385.

Temperature reconstructions for the period of the Wolf minimum are inconsistent and therefore only meaningful to a limited extent. Generally speaking, a fluctuating temperature high can be observed in the first half; in the second half the temperatures then drop to a minimum. Mann and colleagues (1999) situate the maximum shortly after 1300 and the minimum at 1350; they determine the amplitude as 0.35 ° C. Guiot already situates the maximum at 1280 and the minimum at 1320 with an amplitude of 0.6 ° C, whereby the cooling took place with strong fluctuations.

Overall, the climatic development during the wolf minimum can be summed up as follows: the eruption of the Samala in 1257 reduced the solar constant by volcanic radiative forcing by 1.6 watts / square meter and caused a drastic drop in temperature of around 0.4 ° C. By 1270, the climate had largely settled back to its average value. Between 1300 and 1320 there was even a maximum with a solar constant that was 0.1 watt / square meter higher than the average value. Only then did the temperatures drop again to a minimum of 1350 with a solar constant that was 0.15 watt / square meter lower than the average value. This means that the radiative forcing, which has been steadily declining since 1200 due to the wolf minimum, was initially completely covered by the enormous volcanic spike and was only reflected in lower temperatures after 1320 when the volcanic inputs ceased to exist.

Individual evidence

  1. ↑ Stuiver, M. and Quay, PD: Changes in atmospheric carbon-14 attributed to a variable sun . In: Science . tape 207, 11 , 1980.
  2. ↑ a b Usoskin, Ilya G .: A history of solar activity over millenia . In: Living Reviews in Solar Physics . tape 10, 1 , 2013, doi : 10.12942 / lrsp-2013-1 .
  3. ↑ Usoskin, Ilya G. et al .: A millenium scale sunspot number reconstruction: evidence for an unusually active sun since the 1940’s . In: APS / 123-QED . 2008.
  4. ↑ Solanki, SK and Krivova, NA: Solar Irradiance Variations: From Current Measurements to Long-Term Estimates . In: Solar Physics . tape 224 , 2004, pp. 197-208 .
  5. ↑ Usoskin, IG, Solanki, SK, Schüssler, M., Mursula, K. and Alanko, K .: Millennium-Scale Sunspot Number Reconstruction: Evidence for an Unusually Active Sun since the 1940s . In: Phys. Rev. Lett. tape 91, 211101 , 2003.
  6. ↑ Rigozo, NR et al .: Reconstruction of Wolf sunspot numbers on the basis of spectral characteristics and estimates of associated radio flux and solar wind parameters for the last millenium . In: Solar Physics . tape 203 , 2001, p. 179-191 .
  7. ^ Gao, CC, Robock, A. and Ammann, C .: Volcanic forcing of climate over the past 1500 years: An improved ice core-based index for climate models . In: Journal of Geophysical Research-Atmospheres . tape 113 , doi : 10.1029 / 2008JD010239 .
  8. ↑ Holzhauser, H. and Zumbühl, H .: Holocene glacial fluctuations . In: Spreafico, M., Weingartner, R. and Leibundgut, C. (Eds.): Hydrological Atlas of Switzerland . No. 3.8. Bern 1999.
  9. ↑ Holzhauser, H .: Dendrochronological evaluation of fossil woods for the reconstruction of the post-Ice Age glacier history . In: Swiss journal for forestry . tape 15 , 2002, p. 317-337 .
  10. ↑ Michael E. Mann, Raymond S. Bradley, Malcolm K. Hughes: Northern hemisphere temperatures during the past millennium: Inferences, uncertainties, and limitations . In: Geophysical Research Letters . 26, No. 6, March 15, 1999, p. 759. doi : 10.1029 / 1999GL900070 .
  11. ↑ Guiot, J .: The combination of historical documents and biological data in the reconstruction of 1966 climate variations in space and time . In: Frenzel, B., Pfister, C. and Gläser, B. (Eds.): European Climate Reconstructed from Documentary Data: Methods and Results . Gustav Fischer Verlag, Stuttgart, Jena, New York 1992, p. 93-104 .
  12. ↑ Jansen, EJ et al .: Chapter 6: Paleoclimate . In: Climate Change 2007: The Physical Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change . Cambridge University Press, Cambridge and New York 2007, pp. 433-497 .