Oortminimum

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The local minimum is a period of low solar activity in the period 1010 to 1140, with a narrow definition 1040 to 1080.

etymology

The minimum of solar activity is named after the Dutch astronomer Jan Hendrik Oort .

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 Oortminimum, a longer period of below-average solar activity (a Maunder-type minimum), lies shortly before the beginning of the actual Medieval Maximum , which existed between 1150 and 1300 (alternatively also a little earlier between 1100 and 1250). It follows a smaller maximum in the interval 920 to 1020, which some authors have already included in the medieval maximum.

Since the period is long before sunspots are observed , the minimum can only be detected indirectly using proxy data such as the 14 C content in tree rings or the 10 Be content in ice cores . The measured amplitude of the minimum is around 10 ‰ δ 14 C; For example, Usoskin and colleagues (2008) found an amplitude for the local minimum ranging from - 15 to - 5 ‰ δ 14 C. Converted to the reconstructed number of sunspots, this amplitude corresponds to a variation of 5 to 30 sunspots for 14 C (for comparison: the amplitude of the sunspots for the penultimate cycle 23 was 120) and 7 to 40 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

The Oortminimum should have generally brought a slight cooling for the world climate . It thus represents an interruption of the relatively warm temperatures of the Medieval maximum. Compared to the three minima following the Medieval maximum ( Wolf minimum , Spörminimum and Maundermimum) it is significantly weaker. This is already evident from the increased number of sunspots and the parameters radio flux density and solar wind strength , both of which are also higher. The solar radio flux density at a wavelength of 10.7 centimeters for the local minimum is 82.70 ± 32.10, for the medieval maximum 112.40 ± 55.20 and for today's maximum 117.10 ± 53.60 (unit in Watt / square meter x nanometer); the solar wind amounts to 406.00 ± 15.00 for the eastern minimum, 428.00 ± 28.70 for the medieval maximum and 431.10 ± 27.40 for today's maximum (units in kilometers / second). Today's maximum even exceeds the medieval maximum in intensity.

For its part, the local minimum is much more similar to the Dalton minimum between 1790 and 1825 , which has almost identical parameters (84.80 ± 36.10 and 407.60 ± 17.60). The other three minima have much lower values ​​and are therefore also more pronounced in terms of climate (more pronounced cooling).

In Europe, Guiot and colleagues (2010) note a cooling trend in Northern and Eastern Europe for the period 1030 to 1070.

No huge volcanic eruptions are known for the time of the local minimum ; One eruption at 1030 achieved a climate drive through aerosol input of 5 watts / square meter, the rest are smaller eruptions with <3 watts / square meter. The 1030 eruption may have originated from Mount Etna , which entered a period of voluminous volcanic activity between 950 and 1062 (with eruptions around 1000, 1020, 1030 and 1062). An eruption with a caldera collapse on Ceboruco in Mexico has also been dated around the year 1000 . Nelson (1980) also put this outbreak a little later (1020 and 1030).

Individual evidence

  1. ↑ Damon, PE et al: Secular Variation of Δ 14 C during the medieval solar maximum: a proposal report, Proceedings of the 16th International 14C Conference . In: WG Moock and J. van der Plicht (eds.): Radiocarbon . Vol. 40, No. 1 , 1998, p. 343-350 .
  2. ↑ 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. ↑ a b c 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. ↑ Guiot, J., Corona, C. and ESCARSEL members: Growing season temperatures in Europe and climate forcings over the past 1400 years . In: PLoS ONE . 5 (4): e9972, 2010, doi : 10.1371 / journal / pone.0009972 .
  8. ↑ Tanguy, J.-C. ua: Mount Etna eruptions of the last 2750 years: revised chronology and location through archeomagnetic and 226 Ra - 230 Th dating . In: Bulletin of Volcanology . 2007, doi : 10.1007 / S00445-007-0121-X .
  9. ↑ Browne, BL and Gardner, JE: The nature and timing of caldera collapse as indicated by accidental fragments from the AD ~ 1000 eruption of Volcán Ceboruco, Mexico . In: Journal of Volcanology and Geothermal Research . tape 130 , 2004, pp. 93-105 , doi : 10.1016 / S03777-0273 (03) 00283-X .
  10. ^ Nelson, SA: The geology and petrology of Volcán Ceboruco, Nayarit, Mexico . In: Geol. Soc. America Bull. 91, II, 1980, pp. 2290-2431 .