Editing Solar cycle (section)

=== Other hypothesized cycles ===
[[File:Carbon-14-10kyr-Hallstadtzeit Cycles.png|thumb|upright=1.35|2,300 year Hallstatt solar variation cycles]]

Periodicity of solar activity with periods longer than the solar cycle of about 11 (22) years has been proposed, including:
* The Hallstatt cycle (named after a cool and wet [[Hallstatt culture|period in Europe when glaciers advanced]]) is hypothesized to extend for approximately 2,400 years.<ref>{{cite web |url=http://pubs.usgs.gov/fs/fs-0095-00/fs-0095-00.pdf |title=The Sun and Climate |work=U.S. Geological Survey |id=Fact Sheet 0095-00 |access-date=2015-11-17}}</ref><ref>{{cite journal |first1=S. S. |last1=Vasiliev |first2=V. A. |last2=Dergachev |title=The ~ 2400-year cycle in atmospheric radiocarbon concentration: bispectrum of <sup>14</sup>C data over the last 8000 years |journal=Annales Geophysicae |volume=20 |issue=1 |pages=115–20 |year=2002 |doi=10.5194/angeo-20-115-2002 |bibcode=2002AnGeo..20..115V |doi-access=free}}</ref><ref>{{cite journal|vauthors=Usoskin IG, Gallet Y, Lopes F, Kovaltsov GA, Hulot G |title=Solar activity during the Holocene: the Hallstatt cycle and its consequence for grand minima and maxima |journal=Astron. Astrophys. |volume=587 |at=A150 |doi=10.1051/0004-6361/201527295 |arxiv=1602.02483 |bibcode=2016A&A...587A.150U |year=2016 |s2cid=55007495}}</ref><ref>{{cite journal |author=Scafetta, Nicola |author-link=Nicola Scafetta|author2=Milani, Franco|author3=Bianchini, Antonio|author4=Ortolani, Sergio|title=On the astronomical origin of the Hallstatt oscillation found in radiocarbon and climate records throughout the Holocene|journal=Earth-Science Reviews |volume=162 |year=2016 |pages=24–43 |doi=10.1016/j.earscirev.2016.09.004 |arxiv=1610.03096 |bibcode=2016ESRv..162...24S |s2cid=119155024}}</ref>
* In studies of [[carbon-14]] ratios, cycles of 105, 131, 232, 385, 504, 805 and 2,241 years have been proposed, possibly matching cycles derived from other sources.<ref>{{Cite journal|title = The Sun as a low-frequency harmonic oscillator.|url = https://journals.uair.arizona.edu/index.php/radiocarbon/article/view/1450|journal = Radiocarbon|date = 2006-03-31|issn = 0033-8222|pages = 199–205|volume = 34|issue = 2|doi = 10.2458/azu_js_rc.34.1450|first1 = Paul E.|last1 = Damon|first2 = John L.|last2 = Jirikowic}}</ref> Damon and Sonett<ref>Damon, Paul E., and Sonett, Charles P., "Solar and terrestrial components of the atmospheric C-14 variation spectrum," ''In The Sun in Time, Vol. 1'', pp. 360–388, University of Arizona Press, Tucson AZ (1991). [http://adsabs.harvard.edu/abs/1991suti.conf..360D Abstract] (accessed 16 July 2015)</ref> proposed carbon 14-based medium- and short-term variations of periods 208 and 88 years; as well as suggesting a 2300-year radiocarbon period that modulates the 208-year period.<ref name="AZgeos462climsolar">see table in {{cite web|title = Solar Variability: climatic change resulting from changes in the amount of solar energy reaching the upper atmosphere.|work = Introduction to Quaternary Ecology|url = http://www.geo.arizona.edu/palynology/geos462/20climsolar.html|access-date = 2015-07-16|archive-url = https://web.archive.org/web/20050320225607/http://www.geo.arizona.edu/palynology/geos462/20climsolar.html|archive-date = 2005-03-20}}</ref>
* [[Brückner-Egeson-Lockyer cycle]] (30 to 40 year cycles).
* A 2021 study investigates the changes of the Pleistocene climate over the last 800 kyr from European Project for Ice Coring in Antarctica (EPICA) temperature ([[δD]]) and CO<sub>2</sub>-CH<sub>4</sub> records<ref>{{Cite journal |last=Past Interglacials Working Group of PAGES |date=2016 |title=Interglacials of the last 800,000 years |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1002/2015RG000482 |journal=Reviews of Geophysics |language=en |volume=54 |issue=1 |pages=162–219 |doi=10.1002/2015RG000482 |bibcode=2016RvGeo..54..162P |issn=8755-1209|hdl=10261/168880 |hdl-access=free }}</ref> by using the benefits of the full-resolution methodology for time-series decomposition singular spectrum analysis, with a special focus on millennial-scale Sun-related signals.<ref>{{Cite journal |last=Viaggi |first=P. |date=2021 |title=Quantitative impact of astronomical and sun-related cycles on the Pleistocene climate system from Antarctica records |journal=Quaternary Science Advances |volume=4 |pages=100037 |doi=10.1016/j.qsa.2021.100037 |issn=2666-0334|doi-access=free |bibcode=2021QSAdv...400037V }}</ref> The quantitative impact of the three Sun-related cycles (unnamed ~9.7-kyr; proposed 'Heinrich-Bond' ~6.0-kyr; Hallstatt ~2.5-kyr), cumulatively explain ~4.0% (δD), 2.9% (CO<sub>2</sub>), and 6.6% (CH<sub>4</sub>) in variance. A cycle of ~3.6 kyr, which is little known in literature, results in a mean variance of 0.6% only, does not seem to be Sun-related, although a gravitational origin cannot be ruled out. These 800-kyr-long EPICA suborbital records, which include millennial-scale Sun-related signals, fill an important gap in the field of solar cycles demonstrating for the first time the minor role of solar activity in the regional budget of Earth's climate system during the Mid-Late Pleistocene.